[EDToaster]

Adds user post-process shaders (milestone M13). You run ShaderToy/Ghostty-style fragment shaders over the whole terminal, written in GLSL or WGSL, and they hot-reload. The spec is in docs/milestones/m13-user-shaders.md and the README has a new section.

[shader]
paths = ["~/.config/toastty/shaders/crt-splitflap.glsl"]   # chained in order
animation = "auto"                                         # auto | always | never

What's in it

• Languages:
  • GLSL in the ShaderToy dialect (mainImage). It uses the same uniform names and types as Ghostty's shadertoy_prefix.glsl, so Ghostty shaders paste in unchanged.
  • WGSL (fn mainImage(fragCoord: vec2f) -> vec4f, with uniforms read as toastty.iTime etc.).
  • Both go through naga. The y axis points down, as in Ghostty on macOS, so nothing is flipped. Colours are sRGB-encoded, so a pass-through shader reproduces the frame exactly.
• Toastty-only uniforms:
  • iTimeBell, iBellCursor, iBellCount and iBells[4], set from BEL. Each iBells entry holds the cell position, the time of the bell and an exact age computed on the CPU.
  • iCellSize and iGridRect, for effects that work per cell.
  • Term now records each BEL and the cursor cell it rang at. A BEL that ends an OSC string doesn't count.
• Zero idle cost:
  • naga analysis finds which uniforms each shader reads, through helper calls. A shader with no time input draws nothing between events.
  • A shader can declare const float TOASTTY_EVENT_DURATION = 1.5; to animate only for that long after an event it reads (bell, cursor change, focus gain).
  • animation = "auto" stops continuous animation while unfocused and slows to 250 ms frames while occluded.
• Render path: the content pass goes into scratch, then the post passes run (alternating between two textures for a chain), then a UI pass on top. The error banner, close dialog, chips and debug overlay are never shaded. With no shader configured, the frame path is unchanged.
• Errors: compile errors show in the in-window banner as file:line:col, at the right line in your file. The previous working chain keeps running. Shader files are watched and reload on save.
• Demo: examples/shaders/crt-splitflap.glsl. A static CRT look (curvature, scanlines, aperture mask, fringing, vignette). On each bell, a split-flap wave spreads out from the cursor: tiles riffle through characters taken from elsewhere on screen, then land back on their own.

Visual evidence

Real app on Xvfb (1280×800, X11 path), default config plus [shader] paths = ["…/crt-splitflap.glsl"].

The split-flap wave after printf '\a':

Idle: the CRT look on its own (curvature, scanlines, vignette).

Mid-wave: the lighter tiles are flipping, the ones at the edge of the ring are folding over the hinge, and the text inside the ring has already settled.

A broken edit: the error banner names broken2.glsl:196:14 and is drawn unshaded (flat, not curved). The previous shader keeps running.

CPU, measured from /proc/<pid>/stat with the demo shader running:

	utime+stime ticks
idle, 3 s	0
typing one character, next 2 s	0
BackSpace at an empty prompt (bash rings the bell), next 2 s	11 (one ~1.5 s wave, then idle)

Tests

• cargo test --workspace: all pass.
• New toastty-render tests:
  • Unit tests for the preludes and error mapping, the uniform-use analysis (helpers, macros, both languages), the duration constant and its clamp, the event windows, and the uniform layout against naga's offsets.
  • GPU tests: pass-through, invert, chains.
  • End-to-end render_term tests on a new test-only offscreen target:
    • a pass-through chain is pixel-identical to no shader, on both full and partial frames;
    • an inverting chain leaves the banner and overlay unshaded;
    • a mouse event alone triggers a post-only frame;
    • a failed reload keeps the old chain;
    • turning the chain off restores the plain frame.
• New config tests for [shader], shader file path resolution and loading, and the watcher. The watcher tests use real notify events, including symlinked directories and save-by-rename.
• Term BEL tests.
• Clippy: no new warnings in the touched crates (main isn't clippy-clean).

Known limitations

• Transparency: output alpha is presented as is, so a shader that writes alpha = 1 makes a transparent window opaque. The demo keeps the input alpha.
• Upside-down ShaderToy effects: ShaderToy shaders that draw relative to the bottom of the screen come out upside down, as in Ghostty on macOS.
• Permanent delete: a shader file deleted for good is silent. The previous chain keeps running with no banner until the next config reload, because saves by rename look the same as a delete.
• No feedback shaders: there are no multi-buffer ShaderToys (iChannel1+) or feedback buffers.
• Screenshots cover the X11 path only: no Wayland, no HiDPI.