36 lines
2.3 KiB
Markdown
36 lines
2.3 KiB
Markdown
# Render Pipeline Performance Design
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## Goal
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Reduce preview and render CPU cost in the canvas image pipeline so single-node edits no longer trigger repeated full-source decode work, unnecessary histogram work, or duplicated preview renders.
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## Findings
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- `loadSourceBitmap` bypasses the bitmap cache whenever a request is abortable, which is the common path for previews and full renders.
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- Preview rendering always computes a histogram even when the caller does not display one.
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- Multiple UI surfaces can request the same preview work concurrently for the same `sourceUrl`, steps, and preview width.
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- Live preview updates are intentionally low-resolution already, but the system still decodes the full original image before downscaling.
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- Adjustment, compare, and render preview surfaces are all fed by broad graph/context invalidation, so reducing duplicated work inside the preview pipeline gives the best short-term payoff.
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## Chosen Approach
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Implement a targeted hot-path optimization in four small phases:
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1. Repair source image reuse by letting abortable requests share a stable fetch/decode cache instead of bypassing it.
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2. Make histogram generation opt-in at the preview API boundary and disable it for compare/fullscreen preview consumers that do not render histogram UI.
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3. Deduplicate identical in-flight preview requests so the worker and fallback path only compute one preview per unique pipeline fingerprint.
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4. Coalesce live preview updates more aggressively during rapid slider edits so non-urgent preview refreshes do not fan out on every intermediate value.
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## Expected Impact
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- Repeated edits on the same source image reuse decoded bitmap work instead of re-fetching and re-decoding.
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- Compare and fullscreen preview surfaces avoid an unnecessary full-buffer histogram pass.
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- Multiple consumers of the same preview request share one render instead of multiplying CPU work.
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- Slider interactions remain responsive while preview work collapses toward the latest state.
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## Risks
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- Shared source caching must not leak aborted request state into later successful requests.
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- Preview dedupe keys must include every field that changes visible output to avoid stale previews.
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- More aggressive preview coalescing must not break existing expectations around final rendered output or histogram-bearing adjustment previews.
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