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# Conflicts: # crates/codecs/src/exr_stream.rs # crates/codecs/tests/it/exr_stream.rs # crates/io/src/exr_native.rs # crates/io/src/lib.rs # crates/io/tests/it/streaming_exr.rs # docs/roadmap.md # docs/scorecard.md # docs/scratch-disks.md # docs/streaming-io.md # scorecard/reliability.toml
36 lines
2.5 KiB
Markdown
36 lines
2.5 KiB
Markdown
# Viewport pages (GPU canvas for over-budget documents)
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A document's display texture set (every tile, every mip level) is held to the per-document
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canvas budget (`gpu_canvas::budget::canvas_budget`: a quarter of physical memory, capped by a
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discrete GPU's own memory, from the detected RAM and VRAM, so also with GPU Memory on Auto).
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A document whose texture set fits keeps it, with everything around it unchanged: the layer
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budget (LayerFit), deferred refreshes (`DEFER_PX`), background redraw and the compositor's
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output admission. There is no pixel-count cutoff.
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A document whose texture set doesn't fit used to fall back to the CPU canvas
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(`canvasTooLarge`). It is now drawn on the GPU canvas from viewport pages
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(`ui-egui/src/canvas/viewport_pages.rs`, `gpu_canvas/pages.rs`):
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- Pages are 512 texels square at a power-of-two reduction chosen so a texel covers at most one
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screen pixel; a view asks for at most 256 pages and coarsens beyond that. Each page is rendered
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from its core plus a one-texel apron (`photocraft_compose::viewport`), so independently rendered
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pages filter their shared edges identically; the shader discards the apron.
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- Two background workers render pages (over all documents), centre of the view first. At a
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reduction, a faithful document shows a quick nearest-sample preview of every page in view first,
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then the exact (area-averaged) page. Work for a page that left the view, changed zoom or was
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edited is cancelled, and a late result of older work is dropped.
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- Uploads are bounded per frame (2 pages, 32 MB of texels), so staging stays bounded however
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many pages finish at once.
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- Pages are held to half the per-document canvas budget (the rest is headroom for the
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compositor); the least recently wanted pages are evicted first and wanted pages never are.
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The global wgpu resource budget and the split of the GPU memory budget between documents are
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not changed.
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- An edit dirties only the pages its damage (plus the layers' effect reach) touches; a dirty page
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stays on screen until its replacement is uploaded. Invalidation costs the pages held, not the
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document's layers or tiles.
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- When no page fits the budget, or a page fails to render or upload, the document is drawn on the
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CPU canvas as before (`canvasTooLarge`). A failed page is retried when the scratch storage or
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memory configuration changes. Closing the document, a GPU fault or dropping the GPU canvas
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cancels its work and frees its pages. Pattern Preview and size-changing previews keep main's
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path.
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