Add a per-document HDR→SDR mapping applied at the final linear→sRGB encode, so
super-white (HDR) video highlights can be recovered instead of hard-clipped:
- core: HdrOutputMode {Clip (default), HighlightRolloff} on Document (serde
default), with a SetDocumentPropertiesAction variant for undoable edits.
- shaders: a fs_main_rolloff entry point (preview linear_to_srgb.wgsl + the export
inline shader) applying a C1 highlight knee — identity below 0.8, smooth rolloff
[0.8,∞)→[0.8,1). SDR below the knee is untouched; Clip stays the historical path.
- preview (stage.rs) and both export encodes (video_exporter.rs) pick the pipeline
variant from document.hdr_output_mode — one value per frame, so no per-pixel
uniform; mirrors the existing fs_main_straight pattern.
- UI: an "HDR output" dropdown in the Document section of the info panel.
Default (Clip) is bit-identical to previous behaviour. Completes Stage A:
HDR-correct input (pt 1) + SDR-safe output mapping. HDR export (10-bit P010/PQ)
and HDR display remain Stages B/C.
Color correctness:
- Unpremultiply before the sRGB OETF on the display and export blits;
encoding premultiplied color corrupted antialiased/transparent edges.
- Tag exported video as full-range BT.709 (matrix/primaries/transfer).
- Run perception effects (invert, brightness/contrast, hue/saturation)
in gamma space to match standard editors.
- Interpolate gradients in gamma space across the raster and vector paths.
- Render effect thumbnails in the same linear space as the live pipeline.
Brush performance:
- Store the raster canvas as Rgba16Float (no shadow banding from 8-bit
linear), with an incremental per-tile ping-pong sync replacing the
per-frame full-canvas copy.
- Do the linear->sRGB readback conversion on the GPU and reuse a cached
scratch texture, dropping a ~110ms-per-stroke CPU decode.
Cleanup:
- Single COLOR_WGSL prelude and shared CPU sRGB scalars instead of ~8
duplicated copies of the transfer functions.
- Shared compute-pipeline builder; smudge folded onto the tile-sync path.
Skyler Lehmkuhl