perf(web): replace softbuffer canvas present with direct put_image_data#1374
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irvingouj@Devolutions (irvingoujAtDevolution) wants to merge 1 commit into
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perf(web): replace softbuffer canvas present with direct put_image_data#1374irvingouj@Devolutions (irvingoujAtDevolution) wants to merge 1 commit into
irvingouj@Devolutions (irvingoujAtDevolution) wants to merge 1 commit into
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The render path converted each dirty region RGBA -> u32 `0RGB`, then let softbuffer repack u32 -> RGBA into a freshly allocated buffer every frame — two pixel passes over the whole surface plus a per-frame allocation. Replace it with the canvas's own 2D context: one copy of the region into a reused RGBA scratch (alpha forced opaque) followed by put_image_data at the region origin. softbuffer is dropped from ironrdp-web (still used by ironrdp-viewer). Mirrors the same fix in IronVNC. Measured with a record/replay draw bench (dev wasm, headless Chromium), draw-stage median: 4K 1706ms -> 83ms (~20x), 1080p 705ms -> 14ms (~50x), with byte-identical canvas output and unchanged framebuffer checksums.
irvingouj@Devolutions (irvingoujAtDevolution)
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Same as VNC, remove softbuffer |
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irvingouj@Devolutions (irvingoujAtDevolution)
June 12, 2026 21:18
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Pull request overview
This PR updates the ironrdp-web rendering path to remove the softbuffer dependency and present updated regions by uploading RGBA buffers directly to an HTML canvas via CanvasRenderingContext2d::put_image_data, aiming to reduce per-frame work and allocations.
Changes:
- Replaces the softbuffer-based canvas present path with direct
ImageData+put_image_datablits for dirty regions. - Removes the
softbufferdependency fromironrdp-web. - Enables additional
web-sysfeatures needed for 2D canvas rendering (CanvasRenderingContext2d,ImageData).
Reviewed changes
Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| crates/ironrdp-web/src/canvas.rs | Implements the new 2D-context put_image_data rendering path and removes the softbuffer surface logic. |
| crates/ironrdp-web/Cargo.toml | Drops softbuffer dependency; enables required web-sys features for 2D canvas + ImageData. |
| Cargo.lock | Updates lockfile dependency edges to reflect removal of softbuffer from ironrdp-web. |
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| }) | ||
| } | ||
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| /// Setting width/height resets the canvas backing store; the 2D context persists. |
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| pub(crate) fn resize(&mut self, width: NonZeroU32, height: NonZeroU32) { | ||
| self.surface.resize(width, height).expect("surface resize"); | ||
| self.width = width; | ||
| self.canvas.set_width(width.get()); | ||
| self.canvas.set_height(height.get()); |
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What
Removes the
softbufferdependency fromironrdp-weband presents canvas updates via the 2D context'sput_image_datadirectly.Why
The old render path did two full-surface pixel passes per frame (RGBA → u32
0RGB, then softbuffer repacks u32 → RGBA into a freshly allocated buffer) plus a per-frame allocation. The new path does a single copy of each dirty region into a reused RGBA scratch (alpha forced opaque) followed byput_image_dataat the region origin.Perf
Record/replay draw bench (dev wasm, headless Chromium), draw-stage median:
Byte-identical canvas output; unchanged framebuffer checksums. Mirrors the same fix already in IronVNC.
Notes
softbufferis only removed fromironrdp-web;ironrdp-viewer(native) still uses it, so it remains inCargo.lock.CanvasRenderingContext2d+ImageDatafeatures.