Simplify per-terminal theme code; note ansi_colors needs restart

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Architecture.md

@@ -1,24 +1,3 @@
-# vterm architecture
-
-How the plugin is put together, for someone about to change it. `README.md` is the
-user-facing overview; this is the developer reference. Code style lives in `CODE.md`.
-
-## What it is
-
-A terminal emulator that runs inside an ordinary Sublime Text tab. There is no custom
-drawing surface: the emulator's screen is written into the view as **real text**, and
-colours are region overlays. That single decision explains most of what follows.
-
-Constraints it works under:
-
-- **Sublime Text 4**, build 4149+ (`View.folded_regions`), plugin host **Python 3.8**
-  (`.python-version`). The host is a separate process, so every Sublime API call from
-  plugin code is a cross-process round trip — call *count* is what costs.
-- **macOS only.** The pty layer is posix and the mousemap is `Default (OSX)`.
-- Third-party code comes from Package Control libraries declared in `dependencies.json`:
-  `pyte` (emulation), `ptyprocess` (pty), `wcwidth` (character widths).
-- Editing plugin sources needs a **Sublime restart**: submodules are deliberately not
-  purged on reload, because rebuilding the terminal registry would orphan open tabs.
 
 ## Files
 
@@ -30,8 +9,8 @@ Constraints it works under:
 | `vterm/terminal.py` | `Terminal`: pty process, emulator ownership, the reader/renderer threads, and everything written back to the app. |
 | `vterm/emulator.py` | `VtScreen` and `VtStream`: pyte subclasses adding the terminal features these agents need. |
 | `vterm/render.py` | Screen → view text, colour overlays, caret, folding, trimming. |
-| `vterm/scheme.py` | `SchemeManager`: generates the colour scheme that defines the scopes the renderer paints with. |
-| `vterm/themes.py` | The built-in palettes (`default`, `homebrew`, `pro`, `slate`). |
+| `vterm/scheme.py` | `SchemeManager`: generates one theme's colour scheme, the scopes the renderer paints with. `get_scheme_manager` caches one instance per theme name, each terminal frozen to the instance it was opened or rethemed with. |
+| `vterm/themes.py` | The built-in palettes (`default`, `homebrew`, `pro`, `slate`, `red-alert`). |
 | `vterm/commands.py` | The Sublime commands: open, keypress, copy/paste, theme picker, clear, cleanup, close. |
 | `vterm/listeners.py` | `VtermCoreEventListener`: focus, IME capture, copy/paste rerouting, the mousemap context. |
 | `vterm/mouse.py` | Wheel and click handling. |
@@ -100,293 +79,6 @@ Generated at runtime, not in the repo: `Packages/User/vterm/vterm.hidden-color-s
 Two application-wide `EventListener`s: `VtermCoreEventListener` (`listeners.py`) and
 `VtermMouseEventListener` (`mouse.py`).
 
-## Data flows
-
-### Opening a terminal
-
-`vterm_open` → resolve `cmd` (default `$SHELL -l`) and `cwd` (first project folder →
-active file's directory → `~`) → `scheme_manager.initialize()` → `window.new_file()` →
-`vterm_initialize_view` stamps the view settings → `Terminal(view)` → `Terminal.start()`:
-register in `_terminals`, compute the size from the viewport, spawn the pty, build the
-`VtScreen`/`VtStream`, subscribe to palette changes, start the two threads. All on the UI
-thread; a failure closes the view again.
-
-### Output: a pty byte becomes a visible character
-
-```
-child writes
-   │
-   ├─ reader thread ──────────────────────────────────────────────
-   │   process.read(8192)          blocking read on the pty master
-   │   self._decoder.decode(raw)   incremental UTF-8: a sequence split
-   │                               across reads must not be corrupted
-   │   chunks.append(text)         collections.deque, no lock
-   │
-   ├─ renderer thread, every 30 ms (RENDER_PERIOD) ───────────────
-   │   feed_data()                 popleft up to FEED_LIMIT (256 KiB)
-   │   stream.feed(joined)         → VtStream parser → VtScreen.draw
-   │                                 mutates buffer, fills screen.dirty
-   │   in_sync_frame()?            mid ?2026 frame → skip this tick
-   │   is_visible()?               hidden tab → draw nothing this tick
-   │   was_resized()?              (checked once a second) → resize pty
-   │   is_render_due()?           unfocused → at most one frame per
-   │                               UNFOCUSED_RENDER_PERIOD
-   │   _need_to_render()?          dirty rows, a pending clear, or a
-   │                               moved cursor
-   │   view.run_command("vterm_render")
-   │   _sync_wheel_flag()          publishes the mousemap gate
-   │
-   └─ UI thread ──────────────────────────────────────────────────
-       VtermRenderCommand.run(edit)
-         update_lines()   → drain screen.history above `offset`,
-                            then each dirty screen row
-           update_line()  → segment_buffer_line() → row-cache check
-                            → view.replace() + add_regions()
-         sync_alt_fold()
-         follow-scroll gate → trim, focus_cursor()*, request_scroll()
-         sync_cursor_style(), set_name()*, dirty.clear()
-                            * focused terminals only
-```
-
-**Rendering off focus.** A terminal only touches its view the way the user would while it
-holds focus. Sublime dispatches view events application-wide, and packages hang global
-state off them: Vintage's `InputStateTracker.on_selection_modified` resets one module-level
-`g_input_state` for every view in every window, so a caret this plugin moved at 33 fps
-erased the half-typed `d` of a `dd` in whatever file the user was editing. Sublime drops a
-pending key sequence over the same kind of traffic, which took `gg` and `ciw` with it.
-
-Three states, from `Terminal.focused` (set by `on_activated` / `on_deactivated`) and
-`Terminal.is_visible()` (polled once a second, because selecting another tab in an
-unfocused group raises no event for this view):
-
-| state | text | caret, `sel` | tab name | follow-scroll | draw rate |
-| --- | --- | --- | --- | --- | --- |
-| focused | yes | yes | yes | yes | 33 fps |
-| visible, unfocused | yes | no | no | yes | 15 fps |
-| hidden | no | no | no | no | none |
-
-A frame costs a command dispatch and a dozen UI round trips whatever changed — two
-`rowcol(size())`, `folded_regions()`, `viewport_position()`, the `trim_trailing_spaces` scan,
-then `layout_extent()` / `text_to_layout()` / `set_viewport_position()` — so the rate a
-terminal is drawn at is what the editor pays for it, and only a focused one is worth 33 fps.
-
-The renderer tick itself stays at `RENDER_PERIOD` in every state: `feed_data()` runs inside it,
-and throttling that would cap the parser at `FEED_LIMIT` per tick while the reader keeps filling
-an unbounded `chunks`. Only the drawing is rate-limited. So the emulator is always current and
-one render on activation catches the view up. An unfocused terminal is left with an empty selection —
-nothing a render edit can shift, so no selection event of ours escapes — unless the user
-selected text to copy, which is kept.
-
-**The view/offset model.** The view holds real text. Rows `0 .. offset-1` are scrollback;
-rows `offset .. offset + screen.lines - 1` are the live screen. `terminal.offset` is the
-view row of screen row 0. When the emulator retires lines into `screen.history`, the
-renderer drains them, advances `offset` by that many rows, and writes them at their now
-permanent view rows. **Once a line leaves `screen.history`, its only copy is the view
-text** — which is why the alternate screen *folds* the scrollback rather than deleting it.
-
-**The row cache.** pyte's `dirty` set is a repaint *hint*, not a diff: scrolling one line
-marks every row dirty, and a TUI repaints whole frames. `update_line` compares
-`(segments, lf)` against `_row_cache` and returns early when unchanged, which is what
-keeps a full-screen repaint from costing hundreds of cross-process calls.
-
-**The follow-scroll gate.** `following()` compares the viewport against
-`terminal.viewport_y`, where the last auto-scroll left it. Above that, the user scrolled
-up by hand, and trimming, caret placement and scrolling are all skipped so their position
-survives the next frame. `scroll_view` (the PgUp/PgDn and Up/Down chords) closes the gate
-the same way, and scrolling down clamps to the anchor `bottom_y` returns, which re-opens
-it. A one-row scroll lands exactly on the tolerance boundary, so one Up closes the gate
-and one Down re-opens it.
-
-### How colour is actually drawn
-
-`view.add_regions(key, regions, scope)` can only name a **scope**. It cannot take a
-colour. The colours must already exist in the view's colour scheme. So vterm generates
-the colour scheme at runtime:
-
-1. `segment_buffer_line` splits a screen row into runs of identical attributes.
-2. For each non-default run, `scheme_manager.scope(fg, bg, style)` returns a scope name
-   such as `vterm.red.default.b`. On a **miss** it creates the rule and schedules a
-   write; the hot path is a single lock-free dict read.
-3. `colorize_line` calls `add_regions` once per distinct scope in the row, with keys
-   `vterm#N` — monotonic rather than per-row, because `trim_history` renumbers rows and
-   per-row keys would collide. `colored_lines[row]` remembers them so they can be erased.
-   Rows that scroll off the screen are queued by `archive_rows` and merged by
-   `flush_chunk` onto shared `vterm@chunk@scope` keys (one per scope per `CHUNK` rows
-   of scrollback), their per-row keys erased — every key is a separate pass in Sublime's
-   redraw, and a long coloured session used to accumulate ~15k of them. The merge waits
-   for the chunk to close: `add_regions` replaces a key's whole set, so merging every
-   frame re-sent everything the chunk held so far, which is quadratic in `CHUNK` when
-   output arrives a few rows at a time. The open chunk's rows keep their per-row keys
-   until then, so the live count is scopes x chunks plus at most one chunk's worth.
-   Chunk ordinals are view row + `_trimmed`, so `trim_history` renumbering cannot move
-   a row between chunks; trimming settles the open chunk first, then erases whole
-   chunks' keys and compacts the boundary chunk.
-4. `_write_file` serializes every rule into
-   `Packages/User/vterm/vterm.hidden-color-scheme`, the path the view's `color_scheme`
-   setting points at. **Each write makes Sublime reload the scheme and restyle every
-   view**, so writes are debounced 250 ms onto the async thread.
-
-Details worth knowing before touching `scheme.py`:
-
-- Rules are **seeded** at build time for all 16 foregrounds (plain and bold) so the very
-  first frame never references a scope the file lacks.
-- If a rule's resolved background equals the global background *exactly*, it is nudged by
-  one (`next_color`) — `add_regions` inverts foreground and background when they match.
-- Colours are resolved when a rule is added, so a palette change cannot append: `_build`
-  rebuilds the whole table.
-- Truecolor SGR is quantized into the 256 palette (`quantize_256`), which bounds the rule
-  table: every distinct pair would otherwise be a permanent rule and another file write.
-- `plugin_loaded` writes the file **synchronously**, because a restored tab's
-  `color_scheme` is read during startup.
-
-### The alternate screen
-
-While an app owns the alternate buffer, `sync_alt_fold` folds rows `0..offset-1` away, so
-the view shows the app's screen alone. The fold is re-checked every frame, not just on
-transitions, because the screen's first row is rewritten on every region scroll and an
-edit at the fold boundary can silently break a fold. Entering the alt screen collapses the
-layout, so that transition also zeroes `terminal.viewport_y`; a stale anchor would hold
-the follow-scroll gate shut. A fold merely repaired keeps the anchor, or the boundary row
-apps rewrite on every scroll would reset it every frame. The emulator side
-(`switch_to_screen`) swaps in a `maxlen=0` history, so a full-screen app never pushes its
-frames into scrollback.
-
-### Input: a key press reaches the app
-
-Almost every key, **including every printable character**, is bound to `vterm_keypress`.
-That is deliberate: if printables were left to Sublime, an app that does not echo (vim in
-normal mode) would leave the typed character sitting in the view.
-
-```
-keymap binding (context: setting.vterm_view)
-  → VtermKeypressCommand.run(key=…, ctrl=…, alt=…, shift=…)
-  → view_scrolled()          with scroll_modifier, PgUp/PgDn scroll the view a page
-                             and Up/Down a row; stops here, never on the alt screen
-  → Terminal.send_key()      adds application_mode (DECCKM), new_line_mode (LNM)
-  → keys.get_key_code()      modified nav keys → CSI 1;<mod><final>
-                             enter/tab/backspace/space, modified, while the app
-                             asked for modifyOtherKeys → CSI 27;<mod>;<code>~
-                             ctrl → control byte; alt → ESC prefix
-                             plain → _KEY_MAP / _APP_MODE_KEY_MAP
-  → Terminal.send_string(normalized=False)
-  → pty write                ≤4096 bytes inline, larger goes through a queue
-```
-
-**IME and composed input** cannot work this way — there is no key event for "the IME
-committed 日本語"; the text arrives as Sublime's own `insert` command. `on_modified`
-catches that: it reconstructs what was inserted from the caret positions (not from
-`args["characters"]`, which reports the typed keys rather than the committed
-composition), forwards it as an unbracketed paste, and `soft_undo`s any other command
-that modified the view. Text the emulator did not produce must never remain in the view.
-
-**Copy and paste** are rerouted by `on_text_command`: `copy` → `vterm_copy` (which strips
-the zero-width `CONTINUATION` sentinel so soft-wrapped lines re-join), `paste` →
-`vterm_paste`, and `undo` → `vterm_noop`. Pastes are wrapped in `ESC[200~` / `ESC[201~`
-when the app enabled bracketed paste. In the other direction, OSC 52 from the app reaches
-the system clipboard via a hop to the UI thread.
-
-### Mouse
-
-Once per tick, `_sync_wheel_flag` publishes `vterm_view.wheel_captured` = "the app
-reports the mouse, or owns the alternate screen". The mousemap's binding is gated on it,
-which produces three cases:
-
-1. **App tracks the mouse** → `vterm_scroll` maps the event to a screen cell and sends
-   three SGR wheel reports, *one per write* — pi matches the SGR form against a whole
-   stdin chunk and drops anything longer.
-2. **Alternate screen, no tracking** → three arrow keys per notch (alternate scroll, as
-   kitty/iTerm2/xterm do). This is what scrolls a fullscreen UI before it enables mouse
-   reporting.
-3. **Neither** → the binding does not match at all and Sublime scrolls the view over the
-   real scrollback text.
-
-**The trackpad** fires none of that: on macOS it never reaches a mousemap binding
-(sublime_text#1838) and dispatches no command, so a plugin cannot see it at all. Its only
-in-API trace is the viewport moving, and reading a gesture that way means letting the view
-move before pinning it back — visibly, at every poll. vterm does not try: the trackpad is
-converted outside the plugin, by a utility such as LinearMouse set to discrete scrolling
-for Sublime Text, and arrives as ordinary wheel notches on the path above. Nothing in the
-plugin is trackpad-aware, and the viewport is never moved to measure input.
-
-Clicks: `VtermMouseEventListener` intercepts `drag_select` only when the app tracks the
-mouse, and only the plain single-button form, so shift-click and add-selection stay
-native. The first click on an unfocused tab only focuses it — we replaced the command
-that normally does that — and subsequent clicks send a press/release pair.
-
-**The middle button** pastes the view's own selection into the app, as X11 does, and
-never touches the clipboard. The binding is a `press_command`, not a `command`: Sublime's
-own `button3` on macOS is a column `drag_select`, which would clear the selection on
-press before a release command could read it. Shadowing it costs middle-drag column
-select inside terminal tabs; the context makes the binding fall through everywhere else.
-It is not gated on mouse reporting — an empty selection is already a no-op, and the alt
-screen rarely holds one.
-
-### Lifecycle
-
-- **Tab closed** → `on_pre_close` → `Terminal.kill()`: unsubscribe, terminate the child,
-  drop the registry entry.
-- **Process exits** → reader gets `EOFError`, sets `alive = False`; the renderer drains
-  the last output, then posts `vterm_cleanup` to the UI thread. Cleanup latches
-  `vterm_view.finished`, renders a final frame, kills the terminal, and either closes the
-  tab (`auto_close`) or appends `[process exited with code N]`.
-- **Plugin host restart** → the registry is gone but the view survives with its settings
-  and text. `on_activated` detects a view marked `vterm_view` with no terminal behind it
-  and shows a "disconnected" status: the tab has to be closed and reopened.
-
-## Threading
-
-| Thread | Runs | Touches |
-|---|---|---|
-| UI | commands, listeners, `Terminal.start`, `scroll_to_cursor`, clipboard | Sublime API; small pty writes go out here too |
-| reader | `process.read`, decode, `chunks.append` | no Sublime API, no screen state |
-| renderer | `stream.feed`, then `run_command("vterm_render")` | owns the emulator |
-| paste drain | transient; empties the 4096-byte chunk queue | pty only |
-| ST async worker | `SchemeManager._flush` | the scheme file |
-
-The emulator needs no lock because exactly one thread mutates it. The chunk deque needs
-none either: `append` and `popleft` are atomic under the GIL. This matters — the renderer
-used to hold a lock across `stream.feed` **and** the whole render command, so the reader
-could not drain the pty for the duration of a frame and the child blocked in `write()`.
-Backpressure now lives in `FEED_LIMIT` instead: at most 256 KiB is parsed per tick, so a
-huge burst still renders intermediate frames while the reader keeps draining.
-
-`SchemeManager` does keep a lock, because `scope()` is called from the renderer while
-`reload()` and `_flush()` run on other threads. Its read fast path skips the lock; the
-invariant that makes that safe is that `_names` must never outlive `rules` — `_build`
-replaces both together.
-
-## Sublime settings
-
-**Plugin settings** (`vterm.sublime-settings`, read through the cached `settings()`
-handle): `auto_close`, `scrollback_history_size`, `honor_erase_scrollback`,
-`scroll_modifier`, `min_columns`, `max_columns`, `theme`, `ansi_colors`, `terminal`,
-`parameters`, `debug`. `scroll_modifier` is the modifier that turns PgUp/PgDn and Up/Down
-into a scroll of the view — a page, a row — instead of a key for the app. `terminal` and
-`parameters` name the external terminal spawned by *vterm: Open Terminal in Project
-Folder* (`%CWD%` in `parameters` becomes the project folder). ED 3 never touches the visible screen (as in
-xterm), and `honor_erase_scrollback` is off, so it does not drop the scrollback either:
-pi and Claude Code repaint by erasing
-saved lines, which would take the history with them (`cmd+shift+k` still empties the tab). Changing `theme` fires `SchemeManager.reload`, which rebuilds the
-palette and restyles open terminals in place.
-
-**Stamped on every terminal view** by `vterm_initialize_view`: `vterm_view` (the marker
-every context and hook keys off), `is_widget`, `color_scheme` (the generated scheme),
-`syntax` (the empty one), `scroll_past_end` (off — the view never scrolls below the last
-line), `scroll_context_lines`, and a list of disables — `gutter`, `highlight_line`,
-`word_wrap`, `auto_complete`, `draw_white_space`, `draw_indent_guides`, `spell_check`,
-`translate_tabs_to_spaces`, `command_mode` (which
-defuses Vintage mode inside a terminal). The view is also set scratch, so closing it never
-prompts to save.
-
-**Written at runtime**: `vterm_view.finished` (latched by cleanup; also disables the
-Escape binding for a dead tab), `vterm_view.wheel_captured` (the mousemap gate), and
-`block_caret` / `caret_style` (from DECSCUSR; style 0 is the terminal default, a blinking block).
-
-**Contexts.** Keymap bindings use the native `setting.vterm_view`, evaluated in
-Sublime's own process — a plugin `on_query_context` would cost a round trip on every
-keystroke in every view. Mousemaps do **not** evaluate `setting.` contexts the same way,
-so the single wheel context still goes through `on_query_context`, which answers that one
-key and returns `None` for everything else.
 
 ---
 

README.md

@@ -9,17 +9,46 @@ Requires Sublime Text 4 with the Python 3.8 plugin host (build 4149+, for
 
 ## Install
 
-Symlink this folder into Sublime packages as `vterm`:
+### With Package Control
 
-```sh
-ln -s /Users/vaclavt/devel/vt/vterm "$HOME/Library/Application Support/Sublime Text/Packages/vterm"
+vterm is distributed through the shared channel at
+[vaclavt/sublime-chanel](https://github.com/vaclavt/sublime-chanel), not the
+default one. Open **Preferences → Package Settings → Package Control →
+Settings** and put the channel URL in the `channels` array of the right-hand
+(User) pane:
+
+```json
+{
+    "channels": [
+        "https://packagecontrol.io/channel_v3.json",
+        "https://raw.githubusercontent.com/vaclavt/sublime-chanel/main/channel.json"
+    ]
+}
 ```
 
-Dependencies (pyte, ptyprocess, wcwidth) are Package Control libraries declared
-in `dependencies.json`. If they are not yet in `Lib/python38` (e.g. Terminus was
-never installed), run **Package Control: Satisfy Libraries** and restart Sublime.
-Package Control garbage-collects libraries no package requires, so if imports
-ever fail after uninstalling another package, re-run *Satisfy Libraries*.
+Keep `https://packagecontrol.io/channel_v3.json` in the list — dropping it
+hides every default package. Then run **Package Control: Install Package**
+from the Command Palette and pick **vterm**. Upgrades arrive through
+**Package Control: Upgrade Package** like any other package.
+
+### From source
+
+Clone the repository into the Sublime Text `Packages` directory as `vterm`:
+
+```sh
+git clone https://github.com/vaclavt/vterm.git \
+  "$HOME/Library/Application Support/Sublime Text/Packages/vterm"
+```
+
+Use one method or the other, not both: an unpacked `Packages/vterm` directory
+overrides the `vterm.sublime-package` that Package Control installs.
+
+Either way, dependencies (pyte, ptyprocess, wcwidth) are Package Control
+libraries declared in `dependencies.json`. If they are not yet in
+`Lib/python38` (e.g. Terminus was never installed), run **Package Control:
+Satisfy Libraries** and restart Sublime. Package Control garbage-collects
+libraries no package requires, so if imports ever fail after uninstalling
+another package, re-run *Satisfy Libraries*.
 
 ## Use
 
@@ -56,7 +85,9 @@ wheel tick sends arrow keys (alternate scroll, as kitty/iTerm2 do — this is
 what scrolls Claude Code's fullscreen UI before it enables mouse reporting).
 Sublime raises no wheel event at all for the trackpad (sublime_text#1838): set
 a utility such as [LinearMouse](https://linearmouse.app/) to discrete scrolling
-for Sublime Text and it arrives as wheel notches like any other. While an app owns the
+for Sublime Text and it arrives as wheel notches like any other. A notch sends the
+app three scroll lines, as iTerm2 does; `wheel_lines` lowers that when a swipe
+scrolls too far. While an app owns the
 alternate screen the scrollback above it is folded away, kitty-style, and
 unfolds when the app leaves it.
 
@@ -73,11 +104,12 @@ commented out beside it), `debug` (verbose logging to the ST console), plus the
 colours:
 
 - `theme` — `"default"` (Terminal.app Basic, light), `"homebrew"`, `"pro"`,
-  `"slate"`, or `null` to follow the active Sublime colour scheme. Set it with
-  *vterm: Select Theme* or by hand; either way open terminals restyle in place,
-  no restart needed.
+  `"slate"`, `"red-alert"`, or `null` to follow the active Sublime colour scheme. The
+  default for terminals opened from now on. *vterm: Select Theme* retints the
+  focused terminal immediately and sets this; other already-open terminals keep
+  whatever theme they had.
 - `ansi_colors` — override individual base colours, e.g. `{"red": "#ff0000"}`,
-  applied on top of the theme.
+  applied on top of the theme. Takes effect after a Sublime restart.
 
 A light theme is reported to the running agent (OSC 11, DSR 996), so `pi` and
 `claude` switch to their light UI to match. An app subscribed to mode 2031 is also
@@ -154,7 +186,8 @@ instead), image protocols, Windows, panels.
 - Trackpad scrolling needs a helper on macOS: Sublime never delivers it to a
   plugin (sublime_text#1838), so set a utility such as
   [LinearMouse](https://linearmouse.app/) to discrete/linear scrolling for
-  Sublime Text. It then arrives as wheel notches and scrolls the app. Without
+  Sublime Text. It then arrives as wheel notches and scrolls the app, three
+  lines a notch unless `wheel_lines` says otherwise. Without
   one, the trackpad does nothing in a full-screen app; the mouse wheel,
   `shift+pageup/pagedown` and `shift+up/down` work regardless.
 
@@ -167,6 +200,8 @@ python3 tests/test_render.py     # render layer on a fake view: trimming, select
 python3 tests/test_commands.py   # theme picker, live restyle, generated scheme
 python3 tests/harness_live.py CMD SECONDS [--send TEXT]   # run a real app in the emulator, dump the screen
 python3 tools/gen_keymap.py      # regenerate Default.sublime-keymap
+python3 benchmarks/bench_vs_terminus.py   # render cost per frame, against Terminus on the same input
+python3 benchmarks/profiling.py           # feed-path hotspots, per-char micro-benches of draw
 ```
 
 `harness_live.py` is the useful one: it drives a real `pi` or `claude` through the

benchmarks/bench_vs_terminus.py

@@ -0,0 +1,438 @@
+""" Render-cost comparison between vterm and Terminus
+
+Both plugins turn pty output into view text plus add_regions overlays, so what
+they cost the editor is the number of Sublime calls a frame makes -- the plugin
+host is a separate process (see Architecture.md). This drives both render
+commands against a fake view that counts every call, on the same input, with
+each plugin's own render gate deciding when a frame happens.
+
+Terminus is read straight out of its .sublime-package by zipimport; it is
+skipped when not installed. Parse times are real, call counts stand in for the
+cross-process cost, which a fake view cannot show.
+
+Run with: python3 benchmarks/bench_vs_terminus.py
+"""
+import collections
+import os
+import sys
+import time
+
+ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+sys.path.insert(0, os.path.join(ROOT, "tests"))
+import _bootstrap  # noqa: F401  sets sys.path for the imports below
+
+TERMINUS = os.path.expanduser(
+    "~/Library/Application Support/Sublime Text/Installed Packages/Terminus.sublime-package")
+
+import sublime
+
+ROWS, COLUMNS = 40, 100
+SCROLLBACK = 10000
+
+
+class FakeSelection(list):
+    def clear(self):
+        del self[:]
+
+    def add(self, region):
+        self.append(region)
+
+
+class CountingView:
+    """A view that answers with real line arithmetic and tallies every call."""
+
+    _ids = [0]
+
+    def __init__(self, counter):
+        CountingView._ids[0] += 1
+        self._id = CountingView._ids[0]
+        self.c = counter
+        self.text = ""
+        self.selection = FakeSelection()
+        self.regions = {}
+        self.folds = []
+        self._name = ""
+        self._settings = sublime.Settings()
+        # so a plugin that renders through a second command has it counted too
+        self.commands = {}
+
+    def _t(self, name):
+        self.c[name] += 1
+
+    def id(self):
+        return self._id
+
+    def size(self):
+        self._t("size")
+        return len(self.text)
+
+    def rowcol(self, point):
+        self._t("rowcol")
+        head = self.text[:point]
+        return (head.count("\n"), point - (head.rfind("\n") + 1))
+
+    def text_point(self, row, col):
+        self._t("text_point")
+        lines = self.text.split("\n")
+        start = sum(len(l) + 1 for l in lines[:row])
+        return start + min(col, len(lines[row]) if row < len(lines) else 0)
+
+    def _line(self, point):
+        start = self.text.rfind("\n", 0, point) + 1
+        end = self.text.find("\n", point)
+        return sublime.Region(start, len(self.text) if end == -1 else end)
+
+    def line(self, point):
+        self._t("line")
+        return self._line(point)
+
+    def full_line(self, point):
+        self._t("full_line")
+        region = self._line(point)
+        return sublime.Region(region.begin(), min(region.end() + 1, len(self.text)))
+
+    def lines(self, region):
+        self._t("lines")
+        out = []
+        point = region.begin()
+        while point <= region.end():
+            line = self._line(point)
+            out.append(line)
+            point = line.end() + 1
+        return out
+
+    def substr(self, region):
+        self._t("substr")
+        return self.text[region.begin():region.end()]
+
+    def erase(self, edit, region):
+        self._t("erase")
+        self.text = self.text[:region.begin()] + self.text[region.end():]
+
+    def replace(self, edit, region, value):
+        self._t("replace")
+        self.text = self.text[:region.begin()] + value + self.text[region.end():]
+
+    def insert(self, edit, point, value):
+        self._t("insert")
+        self.text = self.text[:point] + value + self.text[point:]
+        return len(value)
+
+    def fold(self, region):
+        self._t("fold")
+        self.folds.append((region.begin(), region.end()))
+        return True
+
+    def unfold(self, region):
+        self._t("unfold")
+        folded, self.folds = self.folds, []
+        return folded
+
+    def folded_regions(self):
+        self._t("folded_regions")
+        return [sublime.Region(a, b) for a, b in self.folds]
+
+    def add_regions(self, key, regions, scope="", *args, **kwargs):
+        self._t("add_regions")
+        # what crosses the process boundary is the regions, not just the call
+        self.c["regions.sent"] += len(regions)
+        self.c["regions.sent.merged" if "@" in key else "regions.sent.row"] += len(regions)
+        self.regions[key] = (scope, [(r.begin(), r.end()) for r in regions])
+
+    def get_regions(self, key):
+        self._t("get_regions")
+        _, spans = self.regions.get(key, ("", []))
+        self.c["regions.read"] += len(spans)
+        return [sublime.Region(a, b) for a, b in spans]
+
+    def erase_regions(self, key):
+        self._t("erase_regions")
+        self.regions.pop(key, None)
+
+    def settings(self):
+        self._t("settings")
+        return CountingSettings(self._settings, self.c)
+
+    def viewport_position(self):
+        self._t("viewport_position")
+        return (0, 0)
+
+    def viewport_extent(self):
+        self._t("viewport_extent")
+        return (800, ROWS * 20)
+
+    def layout_extent(self):
+        self._t("layout_extent")
+        return (800, len(self.text))
+
+    def text_to_layout(self, point):
+        self._t("text_to_layout")
+        return (0, point)
+
+    def set_viewport_position(self, position, animate=True):
+        self._t("set_viewport_position")
+
+    def line_height(self):
+        self._t("line_height")
+        return 20
+
+    def em_width(self):
+        self._t("em_width")
+        return 8
+
+    def name(self):
+        self._t("name")
+        return self._name
+
+    def set_name(self, name):
+        self._t("set_name")
+        self._name = name
+
+    def window(self):
+        self._t("window")
+        return object()
+
+    def sel(self):
+        self._t("sel")
+        return self.selection
+
+    def run_command(self, name, args=None):
+        self._t("run_command:" + name)
+        command = self.commands.get(name)
+        if command:
+            command.run(None, **(args or {}))
+
+
+class CountingSettings:
+    """Settings reads and writes are round trips too, and Terminus does one per run."""
+
+    def __init__(self, settings, counter):
+        self._settings = settings
+        self._c = counter
+
+    def get(self, key, default=None):
+        self._c["settings.get"] += 1
+        return self._settings.get(key, default)
+
+    def set(self, key, value):
+        self._c["settings.set"] += 1
+        self._settings[key] = value
+
+    def erase(self, key):
+        self._c["settings.erase"] += 1
+        self._settings.pop(key, None)
+
+    def has(self, key):
+        return key in self._settings
+
+    def add_on_change(self, *args):
+        pass
+
+    def clear_on_change(self, *args):
+        pass
+
+
+class FakeProcess:
+    def __init__(self):
+        self.writes = []
+
+    def write(self, data):
+        self.writes.append(data)
+
+
+# ------------------------------------------------------------------ workloads
+
+def colour_flood(lines=2000, runs=6, palette=200):
+    """Coloured output: `runs` SGR changes per line, drawn from `palette` colours."""
+    width = COLUMNS // runs
+    out = []
+    for i in range(lines):
+        parts = []
+        for r in range(runs):
+            parts.append("\x1b[38;5;{}m".format(16 + (i * runs + r) % palette))
+            parts.append(str((i + r) % 10) * width)
+        parts.append("\x1b[0m\r\n")
+        out.append("".join(parts))
+    return "".join(out)
+
+
+def plain_flood(lines=2000):
+    return "".join("{:04d} ".format(i) + "x" * (COLUMNS - 5) + "\r\n" for i in range(lines))
+
+
+def tui_repaint(frames=60):
+    """A full-screen coloured app redrawing itself; one cell differs per frame."""
+    out = []
+    for f in range(frames):
+        parts = ["\x1b[H"]
+        for row in range(ROWS):
+            for r in range(4):
+                parts.append("\x1b[38;5;{}m".format(16 + (row * 4 + r) % 200))
+                parts.append(str((row + r) % 10) * (COLUMNS // 4))
+            parts.append("\x1b[0m")
+            if row < ROWS - 1:
+                parts.append("\r\n")
+        parts.append("\x1b[1;1H\x1b[38;5;99m{:04d}\x1b[0m".format(f))
+        out.append("".join(parts))
+    return "".join(out)
+
+
+# ------------------------------------------------------------------- drivers
+
+def drive(feed, need_to_render, render, data, tick):
+    """Feed `data` in tick-sized reads, rendering whenever the plugin asks to."""
+    parse = 0.0
+    frames = 0
+    for i in range(0, len(data), tick):
+        start = time.perf_counter()
+        feed(data[i:i + tick])
+        parse += time.perf_counter() - start
+        if need_to_render():
+            render()
+            frames += 1
+    return parse, frames
+
+
+def run_vterm(data, tick):
+    from vterm.emulator import VtScreen, VtStream
+    from vterm.render import VtermRenderCommand
+    from vterm.terminal import Terminal
+
+    counter = collections.Counter()
+    view = CountingView(counter)
+    terminal = Terminal(view)
+    terminal.scrollback_size = SCROLLBACK
+    terminal.process = FakeProcess()
+    terminal.screen = VtScreen(COLUMNS, ROWS, process=terminal.process, history=SCROLLBACK)
+    Terminal._terminals[view.id()] = terminal
+    stream = VtStream(terminal.screen)
+    command = VtermRenderCommand(view)
+
+    def render():
+        counter["run_command:vterm_render"] += 1
+        command.run(None)
+
+    try:
+        parse, frames = drive(stream.feed, terminal._need_to_render, render, data, tick)
+    finally:
+        del Terminal._terminals[view.id()]
+    return counter, parse, frames, len(view.regions)
+
+
+def run_terminus(data, tick):
+    from terminus.ptty import TerminalScreen, TerminalStream
+    from terminus.render import TerminusRenderCommand, TerminusShowCursorCommand
+    from terminus.terminal import Terminal
+
+    counter = collections.Counter()
+    view = CountingView(counter)
+    terminal = Terminal(view)
+    terminal.detached = False
+    terminal.offset = 0
+    terminal.title = None
+    terminal.default_title = "Terminus"
+    terminal.screen = TerminalScreen(
+        COLUMNS, ROWS, process=FakeProcess(), clear_callback=lambda: None,
+        reset_callback=lambda: None, history=SCROLLBACK)
+    Terminal._terminals[view.id()] = terminal
+    stream = TerminalStream(terminal.screen)
+    command = TerminusRenderCommand(view)
+    command.scrollback_history_size = SCROLLBACK
+    view.commands["terminus_show_cursor"] = TerminusShowCursorCommand(view)
+
+    def render():
+        counter["run_command:terminus_render"] += 1
+        command.run(None)
+        # terminus clears dirty in its render loop, not in the command
+        terminal.screen.dirty.clear()
+
+    try:
+        parse, frames = drive(stream.feed, terminal._need_to_render, render, data, tick)
+    finally:
+        del Terminal._terminals[view.id()]
+    return counter, parse, frames, len(view.regions)
+
+
+# -------------------------------------------------------------------- report
+
+def measure(runner, data, tick):
+    counter, parse, frames, keys = runner(data, tick)
+    calls = sum(v for k, v in counter.items() if not k.startswith("regions."))
+    return {
+        "parse": parse * 1000,
+        "frames": frames,
+        "calls": calls,
+        "per_frame": calls / max(frames, 1),
+        "sent": counter["regions.sent"],
+        "sent_row": counter["regions.sent.row"],
+        "sent_merged": counter["regions.sent.merged"],
+        "read": counter["regions.read"],
+        "keys": keys,
+        "counter": counter,
+    }
+
+
+ROW_FORMAT = "  {:<26}{:>14}{:>14}{:>10}"
+
+
+def report(title, data, tick, both):
+    print("=" * 66)
+    print("{}\n  {:.0f} KiB fed in {} B reads".format(title, len(data) / 1024, tick))
+    print("=" * 66)
+    ours = measure(run_vterm, data, tick)
+    theirs = measure(run_terminus, data, tick) if both else None
+
+    def line(label, key, fmt="{:.0f}"):
+        mine = fmt.format(ours[key])
+        if not theirs:
+            print(ROW_FORMAT.format(label, mine, "-", "-"))
+            return
+        other = fmt.format(theirs[key])
+        ratio = theirs[key] / ours[key] if ours[key] else 0
+        print(ROW_FORMAT.format(label, mine, other, "{:.1f}x".format(ratio)))
+
+    print(ROW_FORMAT.format("", "vterm", "Terminus", "ratio"))
+    line("parse ms", "parse", "{:.1f}")
+    line("frames", "frames")
+    line("sublime calls", "calls")
+    line("calls / frame", "per_frame", "{:.1f}")
+    line("regions sent", "sent")
+    line("  of them merges", "sent_merged")
+    line("regions read back", "read")
+    line("live region keys", "keys")
+    top = sorted(((v, k) for k, v in ours["counter"].items() if not k.startswith("regions.")),
+                 reverse=True)[:6]
+    print("  vterm top: " + ", ".join("{}={}".format(k, v) for v, k in top))
+    if theirs:
+        top = sorted(((v, k) for k, v in theirs["counter"].items() if not k.startswith("regions.")),
+                     reverse=True)[:6]
+        print("  Terminus top: " + ", ".join("{}={}".format(k, v) for v, k in top))
+    print()
+
+
+def main():
+    from vterm.terminal import FEED_LIMIT
+
+    both = os.path.exists(TERMINUS)
+    if both:
+        sys.path.insert(0, TERMINUS)
+    else:
+        print("Terminus is not installed; reporting vterm alone.\n")
+
+    burst = FEED_LIMIT      # the most one renderer tick parses during a flood
+    trickle = 512           # a few rows a frame, as a build log arrives
+
+    report("A. colour flood, 6 runs/line, 200 colours",
+           colour_flood(), burst, both)
+    report("B. colour flood, 6 runs/line, 8 colours",
+           colour_flood(palette=8), burst, both)
+    report("C. colour trickle, a few rows a frame",
+           colour_flood(lines=600), trickle, both)
+    report("D. plain flood, no colour",
+           plain_flood(), burst, both)
+    report("E. TUI repaint, 60 full-screen frames, one cell changes",
+           tui_repaint(), burst, both)
+
+
+if __name__ == "__main__":
+    main()

benchmarks/profiling.py

@@ -0,0 +1,129 @@
+"""Profile the feed/parse path, then micro-bench the per-char steps of VtScreen.draw.
+
+cProfile ranks the hotspots on the bench workloads; the micro loops put numbers
+on the per-char candidates inside the draw path.
+
+Run with: python3 benchmarks/profiling.py
+"""
+import cProfile
+import os
+import pstats
+import sys
+import time
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, HERE)
+sys.path.insert(0, os.path.join(os.path.dirname(HERE), "tests"))
+import _bootstrap  # noqa: F401  sets sys.path for the imports below
+
+from bench_vs_terminus import colour_flood, plain_flood, tui_repaint  # noqa: E402
+from _bootstrap import FakeProcess  # noqa: E402
+from pyte.screens import wcwidth as pyte_wcwidth  # noqa: E402  lru_cache'd
+from wcwidth import wcwidth as raw_wcwidth  # noqa: E402
+
+from vterm.emulator import VtScreen, VtStream  # noqa: E402
+
+
+# ------------------------------------------------------------ feed hotspots
+
+def build():
+    screen = VtScreen(100, 40, process=FakeProcess(), history=10000)
+    return VtStream(screen)
+
+
+def run(name, data):
+    stream = build()
+    t0 = time.perf_counter()
+    for i in range(0, len(data), 32768):
+        stream.feed(data[i:i + 32768])
+    dt = (time.perf_counter() - t0) * 1000
+    print("{:<20} {:.1f} ms".format(name, dt))
+
+
+def profiled(name, data):
+    stream = build()
+    pr = cProfile.Profile()
+    pr.enable()
+    for i in range(0, len(data), 32768):
+        stream.feed(data[i:i + 32768])
+    pr.disable()
+    s = pstats.Stats(pr)
+    print("\n==== {} ====".format(name))
+    s.sort_stats("cumulative").print_stats(18)
+
+
+# ------------------------------------------- per-char micro-benches of draw
+
+data = ("x" * 50 + "\x1b[38;5;100m") * 40000  # ~2M printable chars
+
+
+def t(label, fn, n=3):
+    best = 1e9
+    for _ in range(n):
+        t0 = time.perf_counter()
+        fn()
+        best = min(best, time.perf_counter() - t0)
+    print("{:<42} {:8.3f} ms".format(label, best * 1000))
+
+
+def loop_wcwidth_pyte():
+    for c in data:
+        w = pyte_wcwidth(c)
+
+
+def loop_wcwidth_raw():
+    for c in data:
+        w = raw_wcwidth(c)
+
+
+def loop_iter_only():
+    for c in data:
+        pass
+
+
+def loop_min():
+    x = 0
+    for c in data:
+        x = min(x + 1, 80)
+
+
+def loop_dict_get_set():
+    d = {}
+    line = {}
+    for i, c in enumerate(data):
+        v = d.get(c)
+        if v is None:
+            d[c] = c
+        line[i % 80] = c
+
+
+def loop_min_vs_cmp():
+    x = 0
+    cols = 80
+    for c in data:
+        nx = x + 1
+        x = cols if nx > cols else nx
+
+
+def main():
+    floods = {
+        "colour": colour_flood(),
+        "plain": plain_flood(),
+        "tui": tui_repaint(),
+    }
+    for n, d in floods.items():
+        run(n, d)
+    profiled("colour", colour_flood())
+    profiled("tui", tui_repaint())
+
+    print("==== per-char micro-benches ====")
+    t("iter only", loop_iter_only)
+    t("wcwidth (pyte lru_cache)", loop_wcwidth_pyte)
+    t("wcwidth (raw)", loop_wcwidth_raw)
+    t("min(x+w, cols) per char", loop_min)
+    t("min -> branch per char", loop_min_vs_cmp)
+    t("dict get/miss/set per char", loop_dict_get_set)
+
+
+if __name__ == "__main__":
+    main()

main.py

@@ -5,6 +5,8 @@ registry would orphan open terminal tabs.
 """
 import logging
 
+import sublime
+
 # imported for sublime's command discovery, not called here
 from .vterm.commands import (
     VtermClearScreenCommand,
@@ -28,7 +30,7 @@ from .vterm.mouse import (
     VtermMouseEventListener,
     VtermScrollCommand,
 )
-from .vterm.scheme import scheme_manager
+from .vterm.scheme import build_startup_schemes
 from .vterm.utils import settings
 from .vterm.render import (
     VtermRenderCommand,
@@ -37,9 +39,13 @@ from .vterm.render import (
 
 
 def plugin_loaded():
-    """Write the colour scheme and set the log level, once per plugin host."""
-    # synchronous: a restored tab's color_scheme is read during startup
-    scheme_manager.ensure_file()
+    """Write any missing theme's colour scheme and set the log level, once per
+    plugin host: a restored tab's color_scheme is read during startup and may
+    name any of them.
+    """
+    window = sublime.active_window()
+    view = window.active_view() if window else None
+    build_startup_schemes(view)
 
     level = logging.DEBUG if settings().get("debug", False) else logging.INFO
     logging.basicConfig()

repository.json

@@ -0,0 +1,21 @@
+{
+    "$schema": "sublime://packagecontrol.io/schemas/repository",
+    "schema_version": "4.0.0",
+    "packages": [
+        {
+            "name": "vterm",
+            "details": "https://github.com/vaclavt/vterm",
+            "description": "Minimalist terminal for Sublime Text 4, built to run TUI coding agents (pi, claude) in a tab",
+            "author": "vaclavt",
+            "labels": ["terminal", "shell", "pty"],
+            "releases": [
+                {
+                    "sublime_text": ">=4149",
+                    "platforms": ["osx"],
+                    "python_versions": ["3.8"],
+                    "tags": true
+                }
+            ]
+        }
+    ]
+}

tests/stubs/sublime.py

@@ -87,3 +87,7 @@ def expand_variables(value, variables):
 
 def version():
     return "4200"
+
+
+def active_window():
+    return None

tests/test_commands.py

@@ -5,7 +5,10 @@ from _bootstrap import FakeProcess
 
 import sublime
 from vterm.commands import VtermPasteSelectionCommand, VtermSelectThemeCommand, selection_text
+from vterm.emulator import VtScreen
 from vterm.render import CONTINUATION
+from vterm.scheme import get_scheme_manager
+from vterm.terminal import Terminal
 from vterm.utils import SETTINGS_FILE
 from vterm.themes import THEMES
 
@@ -13,72 +16,113 @@ settings = sublime.load_settings(SETTINGS_FILE)
 panel = {}
 
 
+class FakeTerminalView:
+    """Just enough view for a Terminal to be rethemed: an id and its own settings."""
+
+    _next_id = 1
+
+    def __init__(self):
+        self._id = FakeTerminalView._next_id
+        FakeTerminalView._next_id += 1
+        self._settings = sublime.Settings()
+
+    def id(self):
+        return self._id
+
+    def settings(self):
+        return self._settings
+
+    def is_valid(self):
+        return True
+
+    def style(self):
+        return {}
+
+
 class FakeWindow:
+    def __init__(self, view):
+        self._view = view
+
+    def active_view(self):
+        return self._view
+
     def show_quick_panel(self, items, on_done, selected_index=-1, on_highlight=None):
         panel.update(items=items, on_done=on_done,
                      selected_index=selected_index, on_highlight=on_highlight)
 
 
-def open_picker(current):
-    settings.set("theme", current)
-    command = VtermSelectThemeCommand(FakeWindow())
+def fake_terminal(theme_name):
+    """A terminal frozen to a theme, registered the way a real one is."""
+    view = FakeTerminalView()
+    terminal = Terminal(view, get_scheme_manager(theme_name))
+    terminal.screen = VtScreen(20, 3, process=FakeProcess())
+    Terminal._terminals[view.id()] = terminal
+    return terminal
+
+
+def open_picker(terminal):
+    command = VtermSelectThemeCommand(FakeWindow(terminal.view))
     command.run()
     return command
 
 
 # every theme is offered, with "no theme" first
-command = open_picker(None)
+command = open_picker(fake_terminal(None))
 assert [i[0] for i in panel["items"]] == ["No theme"] + sorted(THEMES), panel["items"]
 assert panel["selected_index"] == 0
 
-# the configured theme starts highlighted
-command = open_picker("pro")
+# the focused terminal's own theme starts highlighted, not the global default
+settings.set("theme", "homebrew")
+terminal = fake_terminal("pro")
+command = open_picker(terminal)
 assert panel["selected_index"] == command.choices.index("pro")
 
-# highlighting previews but must not persist
+# highlighting previews the focused terminal alone, leaving the global default and
+# every other terminal untouched
+other = fake_terminal("default")
 saves = len(sublime._saved)
 panel["on_highlight"](command.choices.index("slate"))
-assert settings.get("theme") == "slate", settings.get("theme")
+assert terminal.scheme.theme_name == "slate", terminal.scheme.theme_name
+assert terminal.view.settings().get("color_scheme") == terminal.scheme.path
+assert other.scheme.theme_name == "default", "another open terminal must not retheme"
+assert settings.get("theme") == "homebrew", "preview must not touch the global default"
 assert len(sublime._saved) == saves, "preview must not save settings"
 
-# cancelling restores the value from before the panel opened
+# cancelling restores the focused terminal's theme from before the panel opened
 panel["on_done"](-1)
-assert settings.get("theme") == "pro", settings.get("theme")
+assert terminal.scheme.theme_name == "pro", terminal.scheme.theme_name
 
-# confirming persists
-command = open_picker("pro")
+# confirming retheme the focused terminal and persists the default for new terminals
+command = open_picker(terminal)
 panel["on_done"](command.choices.index("homebrew"))
+assert terminal.scheme.theme_name == "homebrew", terminal.scheme.theme_name
 assert settings.get("theme") == "homebrew", settings.get("theme")
 assert sublime._saved[-1] == SETTINGS_FILE
+assert other.scheme.theme_name == "default", "another open terminal must not retheme"
 
 # "no theme" persists as null rather than a name
-command = open_picker("slate")
+command = open_picker(fake_terminal("slate"))
 panel["on_done"](0)
 assert settings.get("theme") is None, settings.get("theme")
 
 print("theme picker tests passed ({} themes offered)".format(len(THEMES)))
 
 
-# a palette change must reach terminals that are already running: the screen
-# answers OSC 10/11 and DSR 996 from these values
-from vterm.emulator import VtScreen, VtStream
-from vterm.scheme import scheme_manager
-from vterm.terminal import Terminal
-
+# a palette change must reach the screen it was applied to: it answers OSC 10/11
+# and DSR 996 from these values
+from vterm.emulator import VtStream
 
 recorder = FakeProcess()
-# real __init__ (view unused here); process/screen stand in for start()
-terminal = Terminal(None)
+terminal = fake_terminal("default")
 terminal.screen = VtScreen(20, 3, process=recorder, fg_color="000000",
                            bg_color="ffffff", is_dark=False)
 terminal.process = recorder
 stream = VtStream(terminal.screen)
 
-scheme_manager.foreground = "#eeeeee"
-scheme_manager.background = "#111111"
+terminal.scheme = get_scheme_manager("slate")
 terminal.apply_scheme()
-assert terminal.screen.default_bg_color == "111111", terminal.screen.default_bg_color
-assert terminal.screen.theme_is_dark is True
+assert terminal.screen.default_fg_color == terminal.scheme.foreground.lstrip("#")
+assert terminal.screen.default_bg_color == terminal.scheme.background.lstrip("#")
 
 # without mode 2031 the app is not interrupted
 assert recorder.written == "", repr(recorder.written)
@@ -92,37 +136,30 @@ assert recorder.written == "\x1b[?997;1n", repr(recorder.written)
 # and the emulator answers a colour query with the new palette
 recorder.written = ""
 stream.feed("\x1b]11;?\x07")
-assert recorder.written == "\x1b]11;rgb:1111/1111/1111\x07", repr(recorder.written)
+bg = terminal.screen.default_bg_color
+expected = "\x1b]11;rgb:{0}{0}/{1}{1}/{2}{2}\x07".format(bg[0:2], bg[2:4], bg[4:6])
+assert recorder.written == expected, repr(recorder.written)
 
 print("live theme tests passed (running screen adopts palette, app notified)")
 
 
 # the scheme file must exist before any restored tab's color_scheme is loaded at
-# startup, and building twice must not duplicate the seeded rules
+# startup, and building a theme twice must not duplicate its seeded rules
 import os
-from vterm.scheme import SCHEME_FILE_NAME
 
-path = os.path.join(scheme_manager._directory(), SCHEME_FILE_NAME)
-if os.path.exists(path):
-    os.remove(path)
+scheme = get_scheme_manager("pro")
+path = os.path.join(scheme._directory(), scheme.file_name)
+assert os.path.exists(path), "get_scheme_manager did not write the scheme"
 
-scheme_manager.ensure_file()
-assert os.path.exists(path), "ensure_file did not write the scheme"
-assert not scheme_manager._initialized, \
-    "ensure_file must leave the palette open to refinement by initialize()"
+# the cached instance is reused, not rebuilt
+assert get_scheme_manager("pro") is scheme, "theme managers must be cached"
 
-# a second call is a no-op: same file, untouched
-stamp = os.path.getmtime(path)
-scheme_manager.ensure_file()
-assert os.path.getmtime(path) == stamp, "ensure_file rewrote an existing scheme"
-
-# _build is idempotent, which is what makes the ensure_file + initialize pair safe
-with scheme_manager.lock:
-    scheme_manager._build()
-    first = len(scheme_manager.rules)
-    scheme_manager._build()
-assert len(scheme_manager.rules) == first, \
-    "rules duplicated: {} -> {}".format(first, len(scheme_manager.rules))
+# build is idempotent
+with scheme.lock:
+    first = len(scheme.rules)
+scheme.build()
+assert len(scheme.rules) == first, \
+    "rules duplicated: {} -> {}".format(first, len(scheme.rules))
 
 print("scheme file tests passed ({} seeded rules, idempotent)".format(first))
 

tests/test_imports.py

@@ -63,10 +63,9 @@ assert get_key_code(key="enter", modify_other_keys=2) == "\r", "unmodified keys
 assert get_key_code(key="c", ctrl=True, modify_other_keys=2) == "\x03", "ctrl+c stays a control byte"
 load_sublime_json("Default (OSX).sublime-mousemap")
 
-# scheme manager produces scopes and rules
-import vterm.scheme as scheme_module
-from vterm.scheme import scheme_manager
-scope = scheme_manager.scope("ff0000", "default", "b")
+# a theme's scheme manager produces scopes and rules
+from vterm.scheme import get_scheme_manager
+scope = get_scheme_manager("default").scope("ff0000", "default", "b")
 assert scope == "vterm.ff0000.default.b", scope
 
 # every command referenced by the palette and the keymap must exist, and the
@@ -89,7 +88,7 @@ for entry in load_sublime_json("vterm.sublime-commands") + keymap:
 
 # every pending_* name mentioned in the modules must be a real Terminal
 # attribute, so a renamed flag cannot leave a writer pointing at nothing
-flags = {f for f in vars(Terminal(None)) if f.startswith("pending_")}
+flags = {f for f in vars(Terminal(None, None)) if f.startswith("pending_")}
 assert flags == {"pending_clear", "pending_clear_screen", "pending_render"}, flags
 for module in (commands, render, terminal_module):
     with open(module.__file__, encoding="utf-8") as f:
@@ -114,21 +113,28 @@ for name, theme in THEMES.items():
 configured = load_sublime_json("vterm.sublime-settings").get("theme")
 assert configured is None or configured in THEMES, configured
 
-# plugin_loaded must create the colour scheme: sublime loads a restored tab's
-# color_scheme during startup, before any terminal opens
+# plugin_loaded must create every theme's colour scheme: sublime loads a restored
+# tab's color_scheme during startup, before any terminal opens, and it may name
+# any of them
 # import main.py the way sublime does - as a module of the package directory -
 # so its relative imports and plugin_loaded body are actually executed
+from vterm.scheme import SchemeManager
+from vterm.themes import ALL_THEME_NAMES
+
+scheme_files = [SchemeManager(name).file_path() for name in ALL_THEME_NAMES]
+for scheme_file in scheme_files:
+    if os.path.exists(scheme_file):
+        os.remove(scheme_file)
+
 pkg = types.ModuleType("vterm")
 pkg.__path__ = [ROOT]
 sys.modules["vterm"] = pkg
 main = importlib.import_module("vterm.main")
 
-scheme_file = os.path.join(main.scheme_manager._directory(), scheme_module.SCHEME_FILE_NAME)
-if os.path.exists(scheme_file):
-    os.remove(scheme_file)
 main.plugin_loaded()
-assert os.path.exists(scheme_file), \
-    "plugin_loaded must leave the colour scheme on disk"
+for name, scheme_file in zip(ALL_THEME_NAMES, scheme_files):
+    assert os.path.exists(scheme_file), \
+        "plugin_loaded must leave {}'s colour scheme on disk".format(name)
 
 print("import smoke test passed ({} keymap bindings, {} pending flags, "
       "{} themes)".format(len(keymap), len(flags), len(THEMES)))

tests/test_render.py

@@ -17,6 +17,7 @@ from vterm.render import (
     following,
     scroll_to_cursor,
 )
+from vterm.scheme import get_scheme_manager
 from vterm.terminal import Terminal
 from vterm.utils import SETTINGS_FILE
 
@@ -125,7 +126,9 @@ class FakeView:
         return self.viewport
 
     def set_viewport_position(self, xy, animate=True):
-        self.viewport = xy
+        # scroll_past_end is off, so sublime clamps to the layout
+        maxy = max(0, self.layout_extent()[1] - self.viewport_extent()[1])
+        self.viewport = (xy[0], max(0, min(xy[1], maxy)))
 
     def line_height(self):
         return LINE_HEIGHT
@@ -155,7 +158,7 @@ class FakeView:
 
 def make_terminal(rows=10, cols=20, scrollback=None):
     # real __init__ for the plain attributes; process/screen stand in for start()
-    terminal = Terminal(FakeView())
+    terminal = Terminal(FakeView(), get_scheme_manager("default"))
     if scrollback is not None:
         terminal.scrollback_size = scrollback
     terminal.process = FakeProcess()
@@ -163,9 +166,12 @@ def make_terminal(rows=10, cols=20, scrollback=None):
     return terminal, VtStream(terminal.screen)
 
 
-def make_command(view):
-    # the real __init__, so the fake cannot drift from the command's attributes
-    return VtermRenderCommand(view)
+def make_command(terminal):
+    # the real __init__, so the fake cannot drift from the command's attributes;
+    # run() itself sets _scheme, but these tests call its helpers directly
+    command = VtermRenderCommand(terminal.view)
+    command._scheme = terminal.scheme
+    return command
 
 
 # an app on the alternate screen must not have its view trimmed away: the
@@ -176,7 +182,7 @@ assert terminal.screen.alternate_buffer_mode
 assert terminal.screen.history.maxlen == 0, "alt screen zeroes the deque"
 
 terminal.view = FakeView("\n".join("row {}".format(i) for i in range(10)))
-command = make_command(terminal.view)
+command = make_command(terminal)
 before = terminal.view.text
 command.trim_history(None, terminal)
 assert terminal.view.text == before, \
@@ -186,7 +192,7 @@ assert terminal.view.text == before, \
 terminal, stream = make_terminal(rows=5, scrollback=20)
 terminal.offset = 40
 terminal.view = FakeView("\n".join("row {}".format(i) for i in range(40)))
-command = make_command(terminal.view)
+command = make_command(terminal)
 command.trim_history(None, terminal)
 rows_left = terminal.view.text.count("\n") + 1
 assert rows_left <= 20, rows_left
@@ -197,11 +203,29 @@ assert "row 0" not in terminal.view.text, "oldest rows must be dropped"
 terminal, stream = make_terminal(rows=5, scrollback=5000)
 terminal.offset = 3
 terminal.view = FakeView("\n".join("row {}".format(i) for i in range(8)))
-command = make_command(terminal.view)
+command = make_command(terminal)
 command.trim_history(None, terminal)
 assert "row 0" in terminal.view.text and "row 7" in terminal.view.text, \
     terminal.view.text
 
+# nor may its blank rows be trimmed: an app that blanks and refills its last
+# row (vim's showcmd corner) would resize the view under a pinned viewport
+terminal, stream = make_terminal(rows=4)
+stream.feed("\x1b[?1049h")
+terminal.view = FakeView("top\nrow\n\n")
+command = make_command(terminal)
+before = terminal.view.text
+command.trim_trailing_spaces(None, terminal)
+assert terminal.view.text == before, \
+    "alt screen blank tail was trimmed: {!r}".format(terminal.view.text)
+
+# on the primary screen the blank tail below the cursor still goes
+terminal, stream = make_terminal(rows=4)
+terminal.view = FakeView("top\nrow\n\n")
+command = make_command(terminal)
+command.trim_trailing_spaces(None, terminal)
+assert terminal.view.text == "top\nrow", terminal.view.text
+
 print("render tests passed (alt screen keeps its view, cap honoured)")
 
 
@@ -241,7 +265,7 @@ print("cursor visibility tests passed (hidden cursor keeps the caret)")
 # batches the runs that share a scope into one add_regions call
 terminal, stream = make_terminal(rows=3, cols=20)
 terminal.view = FakeView()
-command = make_command(terminal.view)
+command = make_command(terminal)
 stream.feed("\x1b[31mRED\x1b[0m..\x1b[31mred\x1b[0m..\x1b[32mgreen")
 command.update_lines(None, terminal)
 
@@ -271,7 +295,7 @@ print("colorize tests passed (arithmetic offsets, scope batching, key bookkeepin
 # the whole session, and merging every frame would re-send the whole chunk
 terminal, stream = make_terminal(rows=3, cols=20)
 terminal.view = FakeView()
-command = make_command(terminal.view)
+command = make_command(terminal)
 for i in range(300):
     stream.feed("\x1b[31mred{}\x1b[0m\r\n".format(i))
     command.update_lines(None, terminal)
@@ -290,7 +314,7 @@ assert len(row_keys) == 300 - CHUNK, \
 # trimming settles the open chunk, then erases the keys of chunks above the cut
 terminal, stream = make_terminal(rows=3, scrollback=30)
 terminal.view = FakeView()
-command = make_command(terminal.view)
+command = make_command(terminal)
 stream.feed("".join("\x1b[31mr{}\x1b[0m\r\n".format(i) for i in range(300)))
 command.update_lines(None, terminal)
 terminal.screen.dirty.clear()
@@ -312,7 +336,7 @@ terminal.view.sel().add(sublime.Region(0, 0))       # the caret of a new view
 Terminal._terminals[id(terminal)] = terminal
 terminal.view.id = lambda: id(terminal)
 terminal.default_title = "zsh"
-command = make_command(terminal.view)
+command = make_command(terminal)
 stream.feed("[vterm] %")
 command.run(None)
 assert all(r.empty() for r in terminal.view.sel()), \
@@ -339,10 +363,8 @@ assert all(text == "" for text in rewritten), "unchanged rows were rewritten: {}
 print("render diff tests passed (unchanged dirty rows skipped)")
 
 # the generated scheme must define a selection colour, or sublime uses blue
-from vterm.scheme import blend, scheme_manager
-scheme_manager.background = "#303841"
-scheme_manager.foreground = "#d8dee9"
-assert blend(scheme_manager.background, scheme_manager.foreground, 0.3) == "#626a73"
+from vterm.scheme import blend
+assert blend("#303841", "#d8dee9", 0.3) == "#626a73"
 
 print("selection artefact tests passed (fresh prompt unselected, user selection kept)")
 
@@ -350,7 +372,7 @@ print("selection artefact tests passed (fresh prompt unselected, user selection
 # DECSCUSR drives the caret shape through view settings; before any app asks,
 # and for 0, the caret is the terminal default: a blinking block
 terminal, stream = make_terminal(rows=3, cols=20)
-command = make_command(terminal.view)
+command = make_command(terminal)
 settings = terminal.view.settings()
 
 command.sync_cursor_style(terminal)
@@ -522,6 +544,23 @@ plugin_settings.set("scroll_modifier", "shift")
 print("view scroll tests passed (a screen or a row per press, clamped to the anchor, configurable modifier)")
 
 
+# an app that repaints its block shorter than the screen (pi on every SIGWINCH)
+# leaves the live screen shorter than the viewport once the blank tail is
+# trimmed. the anchor must stay where sublime can actually put the viewport, or
+# the follow gate closes for good and the output is never followed again
+short, _ = make_terminal(rows=8, cols=20)
+short.view.viewport_rows = short.screen.lines
+# 24 scrollback rows, then a live screen holding 3 rows instead of 8
+short.view.text = "\n".join("row {}".format(i) for i in range(27))
+short.offset = 24
+scroll_to_cursor(short.view, short)
+assert short.viewport_y == short.view.viewport_position()[1], \
+    (short.viewport_y, short.view.viewport_position()[1])
+assert following(short.view, short), "follow gate latched shut on a short screen"
+
+print("short screen tests passed (the anchor stays reachable, so the view keeps following)")
+
+
 # shift+enter through the whole keypress path: ESC CR by default, and the CSI 27
 # form once the app turned modifyOtherKeys on, which it reaches for because a
 # bare ESC CR reads as alt+enter
@@ -584,7 +623,7 @@ terminal, stream = make_terminal(rows=5, cols=20)
 terminal.view = FakeView("old1\nold2\nold3\nr0\nr1\nr2\nr3\nr4\n")
 terminal.offset = 3
 terminal.viewport_y = 400
-command = make_command(terminal.view)
+command = make_command(terminal)
 fold_end = terminal.view.text_point(3, 0) - 1
 
 stream.feed("\x1b[?1049h")
@@ -612,7 +651,7 @@ assert terminal.view.folds == [], terminal.view.folds
 # without scrollback there is nothing to fold
 terminal, stream = make_terminal(rows=5, cols=20)
 terminal.view = FakeView("r0\nr1\nr2\nr3\nr4\n")
-command = make_command(terminal.view)
+command = make_command(terminal)
 stream.feed("\x1b[?1049h")
 command.sync_alt_fold(terminal)
 assert terminal.view.folds == [], terminal.view.folds

vterm.sublime-settings

@@ -15,11 +15,16 @@
     // null sends the keys to the app
     "scroll_modifier": "shift",
 
+    // scroll lines sent to the app per wheel notch (iTerm2 sends 3).
+    // A trackpad via LinearMouse makes many notches per swipe; 1 is calmer.
+    "wheel_lines": 1,
+
     "min_columns": 20,
     "max_columns": 500,
 
-    // colour palette: "default", "homebrew", "pro", "slate", or null to
-    // follow the active Sublime colour scheme. Applies to open tabs too.
+    // colour palette: "default", "homebrew", "pro", "slate", "red-alert", or null
+    // to follow the active Sublime colour scheme. Default for terminals opened
+    // from now on; vterm: Select Theme retints the focused terminal and sets this.
     "theme": null,
 
     // override any of the 16 ANSI colors, e.g. {"red": "#ff0000"}

vterm/commands.py

@@ -7,9 +7,9 @@ import sublime
 import sublime_plugin
 
 from .render import CONTINUATION, scroll_view
-from .scheme import SCHEME_PATH, scheme_manager
+from .scheme import get_scheme_manager
 from .terminal import Terminal
-from .themes import THEMES
+from .themes import ALL_THEME_NAMES, THEMES
 from .utils import SETTINGS_FILE, settings
 
 LOG = logging.getLogger(__name__)
@@ -43,12 +43,12 @@ class VtermOpenCommand(sublime_plugin.WindowCommand):
                 cwd = os.path.expanduser("~")
         cwd = sublime.expand_variables(cwd, window.extract_variables())
 
-        scheme_manager.initialize(window.active_view())
+        scheme = get_scheme_manager(settings().get("theme"), host_view=window.active_view())
 
         view = window.new_file()
-        view.run_command("vterm_initialize_view")
+        view.run_command("vterm_initialize_view", {"color_scheme": scheme.path})
 
-        terminal = Terminal(view)
+        terminal = Terminal(view, scheme)
         try:
             terminal.start(cmd, cwd=cwd, env=env, default_title=title or os.path.basename(cmd[0]))
         except Exception:
@@ -106,7 +106,7 @@ class VtermOpenTerminalProjectFolderCommand(sublime_plugin.WindowCommand):
 class VtermInitializeViewCommand(sublime_plugin.TextCommand):
     """Stamps a fresh view with the settings that make it a terminal."""
 
-    def run(self, _):
+    def run(self, _, color_scheme):
         """Apply the view settings; the pty starts only after this."""
         view = self.view
         view_settings = view.settings()
@@ -125,7 +125,7 @@ class VtermInitializeViewCommand(sublime_plugin.TextCommand):
         view_settings.set("draw_indent_guides", False)
         view_settings.set("scroll_past_end", False)
         view_settings.set("scroll_context_lines", 0)
-        view_settings.set("color_scheme", SCHEME_PATH)
+        view_settings.set("color_scheme", color_scheme)
         view_settings.set("syntax", "Packages/vterm/vterm.sublime-syntax")
         view_settings.set("spell_check", False)
         view_settings.set("detect_indentation", False)
@@ -225,13 +225,19 @@ class VtermPasteSelectionCommand(sublime_plugin.TextCommand):
 
 
 class VtermSelectThemeCommand(sublime_plugin.WindowCommand):
-    """Pick a colour palette, previewing each as it is highlighted"""
+    """Retheme the focused terminal, previewing each choice as it is highlighted.
+
+    The chosen theme also becomes the default for terminals opened from now on;
+    it does not touch any other already-open terminal.
+    """
 
     def run(self):
-        """Show the palette picker, starting on the configured theme."""
-        self.settings = settings()
-        self.original = self.settings.get("theme")
-        self.choices = [None] + sorted(THEMES)
+        """Show the palette picker, starting on the focused terminal's own theme."""
+        self.terminal = self._focused_terminal()
+        if not self.terminal:
+            return
+        self.original = self.terminal.scheme.theme_name
+        self.choices = ALL_THEME_NAMES
 
         items = [["No theme", "follow the Sublime color scheme"]]
         for name in self.choices[1:]:
@@ -241,16 +247,36 @@ class VtermSelectThemeCommand(sublime_plugin.WindowCommand):
         current = self.choices.index(self.original) if self.original in self.choices else 0
         self.window.show_quick_panel(items, self._done, selected_index=current, on_highlight=self._preview)
 
+    def is_enabled(self):
+        """Greys the palette entry out when the focused view is not a terminal."""
+        return self._focused_terminal() is not None
+
+    def _focused_terminal(self):
+        """The terminal in the focused view, if any."""
+        view = self.window.active_view()
+        return Terminal.from_id(view.id()) if view else None
+
+    def _apply(self, name):
+        """Retheme the focused terminal alone."""
+        scheme = get_scheme_manager(name, host_view=self.terminal.view)
+        self.terminal.retheme(scheme)
+
     def _preview(self, index):
-        """Apply a palette while it is highlighted, without saving it."""
-        self.settings.set("theme", self.choices[index])
+        """Apply a palette to the focused terminal while it is highlighted."""
+        self._apply(self.choices[index])
 
     def _done(self, index):
-        """Persist the choice, or restore the original if the panel was cancelled."""
+        """On cancel, restore the focused terminal's original theme.
+
+        On confirm, keep the focused terminal on its new theme and persist the
+        choice as the default for terminals opened from now on.
+        """
         if index == -1:
-            self.settings.set("theme", self.original)
+            self._apply(self.original)
             return
-        self.settings.set("theme", self.choices[index])
+        name = self.choices[index]
+        self._apply(name)
+        settings().set("theme", name)
         sublime.save_settings(SETTINGS_FILE)
 
 
@@ -264,6 +290,7 @@ class VtermClearScreenCommand(sublime_plugin.TextCommand):
             return
         # the renderer thread owns the screen; it applies this on its next tick
         terminal.pending_clear_screen = True
+        terminal.wake()
         self.view.run_command("vterm_clear_undo_stack")
 
     def is_enabled(self):

vterm/emulator.py

@@ -93,6 +93,9 @@ def quantize_256(r, g, b):
     return 16 + 36 * level(r) + 6 * level(g) + level(b)
 
 
+# a run of these is width-1 cells only: no wcwidth, no wide/combining cases
+PLAIN_RUN = re.compile("[ -~]+")
+
 # linefeed marks an autowrap (soft wrap), so copy can re-join the halves
 Char = namedtuple(
     "Char",
@@ -147,7 +150,9 @@ class VtScreen(pyte.Screen):
         self._default_char = Char(data=" ", fg="default", bg="default", reverse=False)
         # SGR transitions repeat endlessly in TUI output; memoized per (attrs, params)
         self._sgr_cache = {}
-        # chars are identical while cursor.attrs is unchanged (draw rebuilds per run)
+        # one char -> Char cache per attribute set; attrs recur constantly in
+        # coloured output, so the caches are kept rather than rebuilt on a change
+        self._char_caches = {}
         self._char_cache = {}
         self._cache_attrs = None
         self.history = deque(maxlen=history)
@@ -164,6 +169,8 @@ class VtScreen(pyte.Screen):
         """RIS: reset the screen along with the cursor, scrollback and caches"""
         self._default_char = Char(data=" ", fg="default", bg="default", reverse=False)
         self._sgr_cache.clear()
+        self._char_caches.clear()
+        self._cache_attrs = None
         super().reset()
         self.cursor = Cursor(0, 0)
         self.cursor_style = 0
@@ -331,11 +338,48 @@ class VtScreen(pyte.Screen):
         cursor = self.cursor
         buffer = self.buffer
         columns = self.columns
-        # per-run cache: cells differ only by their data while attrs are unchanged
-        if cursor.attrs is not self._cache_attrs:
-            self._cache_attrs = cursor.attrs
-            self._char_cache = {}
+        attrs = cursor.attrs
+        # cells differ only by their data within one attribute set; the cache is
+        # picked per set, not discarded, or colour changes would thrash it
+        if attrs is not self._cache_attrs:
+            self._cache_attrs = attrs
+            cache = self._char_caches.get(attrs)
+            if cache is None:
+                if len(self._char_caches) > 256:
+                    self._char_caches.clear()
+                cache = self._char_caches[attrs] = {}
+            self._char_cache = cache
         cache = self._char_cache
+
+        if autowrap and not insert_mode and PLAIN_RUN.fullmatch(data):
+            # every cell is width 1, so wraps are pure arithmetic: fill whole
+            # rows with C-speed dict.update instead of looping per char
+            for c in set(data):
+                if c not in cache:
+                    cache[c] = attrs._replace(data=c)
+            get = cache.__getitem__
+            dirty = self.dirty
+            pos = 0
+            length = len(data)
+            while pos < length:
+                x = cursor.x
+                if x == columns:
+                    line = buffer[cursor.y]
+                    last = line[columns - 1]
+                    line[columns - 1] = last._replace(linefeed=True)
+                    dirty.add(cursor.y)
+                    self.carriage_return()
+                    self.linefeed()
+                    x = 0
+                line = buffer[cursor.y]
+                take = min(columns - x, length - pos)
+                end = pos + take
+                line.update(zip(range(x, x + take), map(get, data[pos:end])))
+                dirty.add(cursor.y)
+                cursor.x = x + take
+                pos = end
+            return
+
         line = buffer[cursor.y]
 
         for char in data:
@@ -356,12 +400,12 @@ class VtScreen(pyte.Screen):
                     self.insert_characters(char_width)
                 cell = cache.get(char)
                 if cell is None:
-                    cell = cache[char] = cursor.attrs._replace(data=char)
+                    cell = cache[char] = attrs._replace(data=char)
                 line[cursor.x] = cell
                 if char_width == 2 and cursor.x + 1 < columns:
                     filler = cache.get("")
                     if filler is None:
-                        filler = cache[""] = cursor.attrs._replace(data="")
+                        filler = cache[""] = attrs._replace(data="")
                     line[cursor.x + 1] = filler
             # a combining mark belongs to the cell before it, which may be the
             # last column of the previous row
@@ -391,9 +435,10 @@ class VtScreen(pyte.Screen):
                 break
 
             if char_width > 0:
-                self.cursor.x = min(self.cursor.x + char_width, self.columns)
+                x = cursor.x + char_width
+                cursor.x = x if x < columns else columns
 
-        self.dirty.add(self.cursor.y)
+        self.dirty.add(cursor.y)
 
     def index(self):
         """Line feed; at the bottom of the primary screen the top row goes to scrollback."""

vterm/keys.py

@@ -105,8 +105,7 @@ def _modifier_code(ctrl, alt, shift):
     return 1 + (1 if shift else 0) + (2 if alt else 0) + (4 if ctrl else 0)
 
 
-def get_key_code(key, ctrl=False, alt=False, shift=False, application_mode=False, new_line_mode=False,
-                 modify_other_keys=0):
+def get_key_code(key, ctrl=False, alt=False, shift=False, application_mode=False, new_line_mode=False, modify_other_keys=0):
     """Escape sequence for a key name and its modifiers, honouring the app's active modes"""
     key_lo = key.lower() if len(key) > 1 else key
 

vterm/listeners.py

@@ -27,6 +27,7 @@ class VtermCoreEventListener(sublime_plugin.EventListener):
             # background — via the renderer tick: a render here would race the
             # renderer thread, which owns the emulator
             terminal.pending_render = True
+            terminal.wake()
             view.run_command("vterm_show_cursor", {"scroll": False})
         elif view.settings().get("vterm_view") and not view.settings().get("vterm_view.finished"):
             # the plugin host restarted; this tab's terminal is unreachable

vterm/mouse.py

@@ -8,14 +8,12 @@ notches and take the path below.
 import sublime_plugin
 
 from .terminal import Terminal
+from .utils import settings
 
 # SGR button numbers for the wheel; 64 is the "scroll" bit plus direction
 WHEEL_UP = 64
 WHEEL_DOWN = 65
 
-# lines per wheel tick, as iTerm2 delivers per notch
-WHEEL_LINES = 3
-
 
 def send_scroll(terminal, up, lines, cell=None):
     """Report `lines` scroll lines to the app, or fake arrow keys on the alt screen.
@@ -105,7 +103,8 @@ class VtermScrollCommand(sublime_plugin.TextCommand):
         cell = None
         if terminal.screen.mouse_reporting_enabled() and event:
             cell = _event_to_cell(self.view, terminal, event, clamp=True)
-        send_scroll(terminal, up, WHEEL_LINES, cell)
+        lines = max(0, int(settings().get("wheel_lines", 3)))
+        send_scroll(terminal, up, lines, cell)
 
     def want_event(self):
         """Ask sublime for the wheel coordinates."""

vterm/render.py

@@ -15,7 +15,6 @@ from wcwidth import wcswidth
 # per-cell call in segment_buffer_line
 cell_width = lru_cache(maxsize=4096)(wcswidth)
 
-from .scheme import scheme_manager
 from .terminal import Terminal
 from .utils import rev_wcwidth
 
@@ -124,6 +123,8 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
     def __init__(self, *args, **kwargs):
         """Set up this view's render caches."""
         super().__init__(*args, **kwargs)
+        # the terminal's current SchemeManager; set at the top of each run()
+        self._scheme = None
         self.colored_lines = {}
         # view row -> (segments, lf) as last rendered; the dirty set is only a
         # repaint hint, so most dirty rows are identical frame to frame
@@ -156,6 +157,7 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
         terminal = Terminal.from_id(view.id())
         if not terminal:
             return
+        self._scheme = terminal.scheme
 
         screen = terminal.screen
         # the caret and the tab name are the user's; an unfocused terminal leaves
@@ -316,11 +318,12 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
 
         by_scope = {}
         needed = 0
+        scope_of = self._scheme.scope
         for _, start, end, fg, bg, style in segments:
             if is_default_run(fg, bg, style):
                 continue
             needed = max(needed, end)
-            by_scope.setdefault(scheme_manager.scope(fg, bg, style), []).append((start, end))
+            by_scope.setdefault(scope_of(fg, bg, style), []).append((start, end))
 
         text = "".join(s[0] for s in segments)
         if lf:
@@ -380,6 +383,7 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
 
         grouped = {}
         stale = []
+        scope_of = self._scheme.scope
         for row in rows:
             keys = self.colored_lines.pop(row, None)
             if not keys:
@@ -391,7 +395,7 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
             for _, a, b, fg, bg, style in segments:
                 if is_default_run(fg, bg, style):
                     continue
-                scope = scheme_manager.scope(fg, bg, style)
+                scope = scope_of(fg, bg, style)
                 grouped.setdefault(scope, []).append(sublime.Region(start + a, start + b))
 
         scopes = self._archived_chunks.setdefault(chunk, set())
@@ -410,9 +414,16 @@ class VtermRenderCommand(sublime_plugin.TextCommand):
 
         Without this the view keeps a full screen of blank rows below a short
         prompt, and the scrollbar reflects them.
+
+        Both are skipped on the alternate screen, where the app owns every row:
+        one that blanks and refills - vim's showcmd corner, on every keypress -
+        would resize the view under a viewport pinned to its bottom, and the
+        whole screen shifts by the part of a row the viewport leaves over.
         """
         view = self.view
         screen = terminal.screen
+        if screen.alternate_buffer_mode:
+            return
         cursor = screen.cursor
         cursor_row = terminal.offset + cursor.y
         lastrow = view.rowcol(view.size())[0]
@@ -513,11 +524,10 @@ def following(view, terminal):
 
 
 def bottom_y(view, terminal):
-    """Viewport y that pins the bottom of the live screen to the bottom of the view."""
+    """Viewport y that pins the bottom of the view to the bottom of the viewport."""
+
     # layout_extent is maintained incrementally, unlike text_to_layout(size())
-    viewport_y = view.layout_extent()[1] - view.viewport_extent()[1]
-    offset_y = view.text_to_layout(view.text_point(terminal.offset, 0))[1]
-    return max(offset_y, viewport_y)
+    return max(0, view.layout_extent()[1] - view.viewport_extent()[1])
 
 
 def scroll_to_cursor(view, terminal):

vterm/scheme.py

@@ -8,16 +8,12 @@ import sublime
 
 from .emulator import ANSI_COLORS
 from .utils import settings
-from .themes import THEMES
+from .themes import ALL_THEME_NAMES, THEMES
 
 LOG = logging.getLogger(__name__)
 
 # written under Packages/User so it survives a package reinstall
 SCHEME_DIR_NAME = "User/vterm"
-# "hidden-" keeps the generated scheme out of the scheme picker
-SCHEME_FILE_NAME = "vterm.hidden-color-scheme"
-# the value terminal views get as their color_scheme setting
-SCHEME_PATH = "Packages/{}/{}".format(SCHEME_DIR_NAME, SCHEME_FILE_NAME)
 
 # each write makes sublime reload the scheme and restyle every view
 WRITE_DEBOUNCE_MS = 250
@@ -69,104 +65,61 @@ def _is_dark(color_text):
 
 
 class SchemeManager:
-    """Owns the generated scheme file and the set of known scopes."""
+    """Owns one theme's generated scheme file and set of known scopes."""
 
-    def __init__(self):
-        """Start on the built-in palette; initialize() picks up the real one."""
+    def __init__(self, theme_name):
+        """State only; build() resolves the palette and writes the file."""
+        self.theme_name = theme_name
+        self.file_name = "vterm-{}.hidden-color-scheme".format(theme_name or "system")
+        self.path = "Packages/{}/{}".format(SCHEME_DIR_NAME, self.file_name)
         self.lock = threading.Lock()
         self.rules = {}
         # key -> scope name; the render thread reads it without the lock, so it
-        # must never outlive self.rules (cleared together in _build)
+        # must never outlive self.rules (cleared together in build)
         self._names = {}
         self.foreground = "#ffffff"
         self.background = "#000000"
-        self._editor_fg = "#ffffff"
-        self._editor_bg = "#000000"
         self.ansi = dict(DEFAULT_ANSI)
         self._write_pending = False
-        self._initialized = False
         self._dir = None
-        self._host_view = None
-        self._listeners = []
 
-    def initialize(self, view):
-        """Pick up the palette, seed the rules, write the file. Main thread only"""
-        if self._initialized:
-            return
-        self._initialized = True
-        self._host_view = view
-
-        settings().add_on_change("vterm.theme", self.reload)
-        self._build()
-
-    def ensure_file(self):
-        """Write the scheme if missing: a restored tab's color_scheme is loaded during startup"""
-        if os.path.exists(os.path.join(self._directory(), SCHEME_FILE_NAME)):
-            return
-        with self.lock:
-            self._build()
-
-    def add_listener(self, callback):
-        """Called after every palette rebuild"""
-        self._listeners.append(callback)
-
-    def remove_listener(self, callback):
-        """Drop a rebuild subscriber; terminals unsubscribe when they die."""
-        if callback in self._listeners:
-            self._listeners.remove(callback)
-
-    def reload(self):
-        """Rebuild every rule for a new palette, then notify the terminals"""
-        if not self._initialized:
-            # no scheme file to maintain yet; initialize() will read the setting
-            return
-        with self.lock:
-            self._build()
-        for callback in list(self._listeners):
-            try:
-                callback()
-            except Exception:
-                LOG.warning("scheme listener failed", exc_info=True)
-
-    def _build(self):
+    def build(self, host_view=None):
         """Resolve the palette and regenerate every rule, then write the file.
 
         Rules cannot be appended after a palette change: each one stores resolved
-        colours, so they all have to be rebuilt. Caller holds the lock.
+        colours, so they all have to be rebuilt. Callable again later (e.g. to
+        re-sample the "No theme" palette from the editor's current colours).
         """
-        self._names = {}
-        self.rules = {}
-        self.ansi = dict(DEFAULT_ANSI)
+        with self.lock:
+            self._names = {}
+            self.rules = {}
+            self.ansi = dict(DEFAULT_ANSI)
 
-        theme = THEMES.get(settings().get("theme"))
+            theme = THEMES.get(self.theme_name)
 
-        if theme:
-            self.foreground = theme["foreground"]
-            self.background = theme["background"]
-            self.ansi.update({name: theme[name] for name in ANSI_COLORS if name in theme})
-        else:
-            # captured values outlive the view they came from
-            if self._host_view is not None and self._host_view.is_valid():
-                style = self._host_view.style()
-                self._editor_fg = style.get("foreground", self._editor_fg)
-                self._editor_bg = style.get("background", self._editor_bg)
-            self.foreground = self._editor_fg
-            self.background = self._editor_bg
+            if theme:
+                self.foreground = theme["foreground"]
+                self.background = theme["background"]
+                self.ansi.update({name: theme[name] for name in ANSI_COLORS if name in theme})
+            elif host_view is not None and host_view.is_valid():
+                style = host_view.style()
+                self.foreground = style.get("foreground", self.foreground)
+                self.background = style.get("background", self.background)
 
-        # user overrides sit on top of whichever palette was chosen
-        user_ansi = settings().get("ansi_colors", {})
-        for name in ANSI_COLORS:
-            if name in user_ansi:
-                self.ansi[name] = user_ansi[name]
+            # user overrides sit on top of whichever palette was chosen
+            user_ansi = settings().get("ansi_colors", {})
+            for name in ANSI_COLORS:
+                if name in user_ansi:
+                    self.ansi[name] = user_ansi[name]
 
-        # seeded so the first frame does not reference scopes the file lacks
-        for fg in ANSI_COLORS:
-            self._add_rule(fg, "default", "")
-            self._add_rule(fg, "default", "b")
-        self._add_rule("default", "default", "b")
-        self._add_rule("reverse_default", "reverse_default", "")
+            # seeded so the first frame does not reference scopes the file lacks
+            for fg in ANSI_COLORS:
+                self._add_rule(fg, "default", "")
+                self._add_rule(fg, "default", "b")
+            self._add_rule("default", "default", "b")
+            self._add_rule("reverse_default", "reverse_default", "")
 
-        self._write_file()
+            self._write_file()
 
     def is_dark(self):
         """Whether the active palette is dark; reported to the app via OSC 11 and DSR 996."""
@@ -228,6 +181,10 @@ class SchemeManager:
             rule["font_style"] = " ".join(font_style)
         self.rules[(fg, bg, style)] = rule
 
+    def file_path(self):
+        """Filesystem path of the generated scheme file."""
+        return os.path.join(self._directory(), self.file_name)
+
     def _directory(self):
         """Path of the generated scheme's directory, created on first use."""
         if self._dir is None:
@@ -258,11 +215,49 @@ class SchemeManager:
             },
             "rules": list(self.rules.values()),
         }
-        path = os.path.join(self._directory(), SCHEME_FILE_NAME)
-        with open(path, "w", encoding="utf-8") as f:
+        with open(self.file_path(), "w", encoding="utf-8") as f:
             # compact: sublime reparses the whole file on every write
             json.dump(scheme, f, separators=(",", ":"))
         LOG.debug("scheme written: rules=%s", len(self.rules))
 
 
-scheme_manager = SchemeManager()
+# one manager per theme name, built once and kept for the plugin host's life: the
+# built-in theme set is small and fixed, so there is nothing to garbage-collect
+_managers = {}
+
+
+def get_scheme_manager(theme_name, host_view=None):
+    """The manager for a theme name (None for "follow the Sublime colour scheme"),
+    building and caching it on first use.
+
+    The None entry is rebuilt whenever the editor's colours have changed since: it
+    is a live sample of them, not a static palette, so every caller handing a
+    terminal a "no theme" scheme gets one that is actually current.
+    """
+    manager = _managers.get(theme_name)
+    if manager is None:
+        manager = SchemeManager(theme_name)
+        _managers[theme_name] = manager
+        manager.build(host_view)
+    elif theme_name is None and host_view is not None and host_view.is_valid():
+        style = host_view.style()
+        if (style.get("foreground"), style.get("background")) != (manager.foreground, manager.background):
+            manager.build(host_view)
+    return manager
+
+
+def build_startup_schemes(host_view=None):
+    """Make sure every theme's colour scheme is on disk before Sublime reads a
+    restored tab's color_scheme at startup.
+
+    A named theme is static, so an existing file is left alone - rebuilding it
+    would just rewrite the same bytes, and each write makes sublime reload the
+    scheme and restyle every view using it. None always rebuilds, same as
+    get_scheme_manager.
+    """
+    for name in ALL_THEME_NAMES:
+        if name is None:
+            get_scheme_manager(None, host_view=host_view)
+            continue
+        if not os.path.exists(SchemeManager(name).file_path()):
+            get_scheme_manager(name)

vterm/terminal.py

@@ -13,7 +13,6 @@ from pyte import modes as mo
 
 from .emulator import APP_CURSOR_MODE, VtScreen, VtStream
 from .keys import get_key_code
-from .scheme import scheme_manager
 from .utils import intermission, responsive, settings
 
 LOG = logging.getLogger(__name__)
@@ -24,12 +23,24 @@ RENDER_PERIOD = 0.03
 # draw rate for a visible terminal the user is not typing in, ~15 fps
 UNFOCUSED_RENDER_PERIOD = 0.075
 
-# max chars parsed per tick, so a giant burst still renders intermediate frames
-FEED_LIMIT = 256 * 1024
+# max chars parsed per tick, so a giant burst still renders intermediate frames.
+FEED_LIMIT = 48 * 1024
 
 # SUPPRESS_HISTORY_AFTER_CLEAR in emulator.py must outlast this
 REPAINT_NUDGE_DELAY = 0.25
 
+# extra wait once a tick finds nothing pending, on top of RENDER_PERIOD.
+IDLE_TICK = 0.2
+
+# pause before the first frame after an idle park, so the writes of one app
+# update land together: vim splits every keypress into two writes a fraction of
+# a millisecond apart, and drawing between them flashes its showcmd echo
+SETTLE = 0.005
+
+# frames between undo-stack clears: every render edit lands on the view's undo
+# stack, which only focus changes clear otherwise, and undo is swallowed anyway
+UNDO_CLEAR_FRAMES = 100
+
 
 def view_size(view, default=None):
     """Terminal (rows, columns) that fit the view's viewport."""
@@ -86,9 +97,10 @@ class Terminal:
 
     _terminals = {}
 
-    def __init__(self, view):
+    def __init__(self, view, scheme):
         """State only; the pty and the threads come up in start()."""
         self.view = view
+        self.scheme = scheme
         # process.isalive() costs two waitpid syscalls; UI hooks read this instead
         self.alive = True
         self.default_title = ""
@@ -116,6 +128,12 @@ class Terminal:
         self.pending_render = False
         # a UTF-8 sequence split across read chunks must not be dropped
         self._decoder = codecs.getincrementaldecoder("utf-8")("replace")
+        # set by the reader (and the UI thread) to end the renderer's idle park
+        self._wake = threading.Event()
+
+    def wake(self):
+        """Cut short the renderer's idle wait, for a flag set from another thread"""
+        self._wake.set()
 
     @classmethod
     def from_id(cls, vid):
@@ -180,12 +198,11 @@ class Terminal:
             erase_scrollback=settings().get("honor_erase_scrollback", False),
             clear_callback=self._clear_callback,
             clipboard_callback=self._clipboard_callback,
-            fg_color=scheme_manager.foreground.lstrip("#"),
-            bg_color=scheme_manager.background.lstrip("#"),
-            is_dark=scheme_manager.is_dark(),
+            fg_color=self.scheme.foreground.lstrip("#"),
+            bg_color=self.scheme.background.lstrip("#"),
+            is_dark=self.scheme.is_dark(),
         )
         self.stream = VtStream(self.screen)
-        scheme_manager.add_listener(self.apply_scheme)
 
         self._start_rendering()
 
@@ -193,17 +210,25 @@ class Terminal:
         """Adopt a new palette; mode 2031 subscribers are told so they can restyle"""
         # the screen answers OSC 10/11 and DSR 996 from these values
         screen = self.screen
-        screen.default_fg_color = scheme_manager.foreground.lstrip("#")
-        screen.default_bg_color = scheme_manager.background.lstrip("#")
-        screen.theme_is_dark = scheme_manager.is_dark()
+        screen.default_fg_color = self.scheme.foreground.lstrip("#")
+        screen.default_bg_color = self.scheme.background.lstrip("#")
+        screen.theme_is_dark = self.scheme.is_dark()
         if screen.theme_notify_enabled():
             self.send_string(screen.theme_report(), normalized=False)
 
+    def retheme(self, scheme):
+        """Switch to a different scheme: vterm: Select Theme, scoped to this terminal."""
+        if scheme is self.scheme:
+            return
+        self.scheme = scheme
+        self.view.settings().set("color_scheme", scheme.path)
+        self.apply_scheme()
+
     def kill(self):
         """Terminate the child and drop this terminal from the registry."""
         LOG.debug("[kill] terminating process")
         self.alive = False
-        scheme_manager.remove_listener(self.apply_scheme)
+        self._wake.set()
         try:
             self.process.terminate()
         except Exception:
@@ -254,11 +279,13 @@ class Terminal:
                 except EOFError:
                     break
                 chunks.append(self._decoder.decode(raw))
+                self._wake.set()
                 if done[0] or not self.is_hosted():
                     LOG.debug("[reader] stops")
                     break
             self.alive = False
             done[0] = True
+            self._wake.set()
 
         def feed_data():
             """Parse up to FEED_LIMIT of pending output into the screen."""
@@ -278,11 +305,13 @@ class Terminal:
 
         def renderer():
             """Own the emulator: parse, then ask sublime to redraw, once per tick."""
+            frames = 0
             while True:
                 # a hidden tab is not drawn at all: the screen keeps the state
-                # and one render on unhide catches the view up. The tick stays at
-                # full rate either way, or the parser would fall behind the pty
+                # and one render on unhide catches the view up.
                 visible = self.is_visible()
+
+                self._wake.clear()
                 with intermission(period=RENDER_PERIOD):
                     feed_data()
                     if self.screen.in_sync_frame():
@@ -295,11 +324,26 @@ class Terminal:
                         # due first: _need_to_render consumes the cursor move it reports
                         if self.is_render_due() and self._need_to_render():
                             self.view.run_command("vterm_render")
+                            frames += 1
+                            if frames >= UNDO_CLEAR_FRAMES:
+                                frames = 0
+                                self.view.run_command("vterm_clear_undo_stack")
                     self._sync_wheel_flag()
                     if done[0] or not self.is_hosted():
                         LOG.debug("[renderer] stops")
                         break
 
+                # nothing left to do: park until woken, instead of spinning at
+                # RENDER_PERIOD. A sync frame or a teardown skipped this by
+                # leaving the block above, and keeps its own cadence.
+                # dirty rows only count while visible: nothing clears them for a
+                # hidden tab, and on_activated wakes us with pending_render
+                if not (
+                    chunks or self.pending_render or self.pending_clear or self.pending_clear_screen or (visible and self.screen.dirty)
+                ):
+                    if self._wake.wait(IDLE_TICK):
+                        time.sleep(SETTLE)
+
             while chunks:
                 feed_data()
             done[0] = True

vterm/themes.py

@@ -50,4 +50,27 @@ THEMES = {
         "light_cyan": "#8cdfe0",
         "light_white": "#e0e0e0",
     },
+    "red-alert": {
+        "foreground": "#ffffff",
+        "background": "#762423",
+        "black": "#000000",
+        "red": "#d62e4e",
+        "green": "#71be6b",
+        "brown": "#beb86b",
+        "blue": "#489bee",
+        "magenta": "#e979d7",
+        "cyan": "#6bbeb8",
+        "white": "#d6d6d6",
+        "light_black": "#262626",
+        "light_red": "#e02553",
+        "light_green": "#aff08c",
+        "light_brown": "#dfddb7",
+        "light_blue": "#65aaf1",
+        "light_magenta": "#ddb7df",
+        "light_cyan": "#b7dfdd",
+        "light_white": "#ffffff",
+    },
 }
+
+# every selectable theme, including None for "follow the active Sublime colour scheme"
+ALL_THEME_NAMES = [None] + sorted(THEMES)