tui: image rendering — sixel backend #13

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opened 2026-04-11 13:01:09 +00:00 by charles · 0 comments

charles commented

2026-04-11 13:01:09 +00:00

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User story

As a user on a sixel-capable terminal (xterm -ti 340, mlterm, wezterm, foot), I want loom-tui to display images using the sixel protocol when Kitty is unavailable, so that I still get colour images without falling back to block art.

Acceptance criteria

Sixel renderer

SixelRenderer struct implements ImageRenderer (trait from the Kitty ticket)
Primary path: use the sixel crate for encoding; fallback: shell out to img2sixel when the crate is unavailable on the target, behind a cargo feature
Output clamped to the passed Rect dimensions (respecting terminal cell-to-pixel ratio, queried via crossterm / ioctl TIOCGWINSZ)
protocol_name() returns "sixel"
Redraws on resize are debounced so scrolling does not flood the terminal
Unit test: a fixed 64×64 PNG encodes to a deterministic sixel payload prefix (\x1bPq)

Caching

Shares the same (source, width, height) cache key semantics as the Kitty backend
Cached sixel bytes reused across frames; eviction on resize

Out of scope

Kitty backend (separate ticket)
Chafa fallback (separate ticket)
Protocol auto-detection (separate ticket)

References

Spec §2.2 "Image Rendering Subsystem"
DEC Sixel graphics spec

## User story As a user on a sixel-capable terminal (xterm -ti 340, mlterm, wezterm, foot), I want loom-tui to display images using the sixel protocol when Kitty is unavailable, so that I still get colour images without falling back to block art. ## Acceptance criteria ### Sixel renderer - [ ] `SixelRenderer` struct implements `ImageRenderer` (trait from the Kitty ticket) - [ ] Primary path: use the `sixel` crate for encoding; fallback: shell out to `img2sixel` when the crate is unavailable on the target, behind a cargo feature - [ ] Output clamped to the passed `Rect` dimensions (respecting terminal cell-to-pixel ratio, queried via crossterm / `ioctl TIOCGWINSZ`) - [ ] `protocol_name()` returns `"sixel"` - [ ] Redraws on resize are debounced so scrolling does not flood the terminal - [ ] Unit test: a fixed 64×64 PNG encodes to a deterministic sixel payload prefix (`\x1bPq`) ### Caching - [ ] Shares the same `(source, width, height)` cache key semantics as the Kitty backend - [ ] Cached sixel bytes reused across frames; eviction on resize ## Out of scope - Kitty backend (separate ticket) - Chafa fallback (separate ticket) - Protocol auto-detection (separate ticket) ## References - Spec §2.2 "Image Rendering Subsystem" - DEC Sixel graphics spec

charles added this to the loom-tui v0.1.0 milestone

2026-04-11 13:01:09 +00:00

charles added the

area:image

type:user-story

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2026-04-11 13:01:09 +00:00

charles referenced this issue

2026-04-11 13:07:50 +00:00

tui: tracking — loom-tui v0.1.0 roadmap & implementation order #47

charles referenced this issue

2026-04-11 15:22:44 +00:00