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Fix seals inside layers, gradient repetition and WebGPU scratch bounds - #428
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Gradient brushes with Repeat and Reflect now repeat before the start point. Repeat subtracts the floor of the position, and Reflect uses the magnitude of the position. The WebGPU shaders use the same rules. Flush, RenderScene, CreateScene and CopyPixelsFrom inside an open layer keep the layer whole. A retained scene renders inside a layer on both backends. The WebGPU encoder reads it in place through a scene segment table. CopyPixelsFrom inside a layer reads the source rectangle with ReadRegion and draws the image into the layer with Src. The WebGPU encoder computes upper bounds for the scratch buffers, with row bounds for tile-row chunks and blend depth regions for the blend spill. fine adds the coverage of each pixel in fixed point, so the output does not depend on the GPU scheduling order, and it equals the CPU output. An offscreen WebGPU render checks its scratch status before it returns, and it renders again with larger buffers after an overflow. The deferred corrective re-render is removed, so a scene releases its resources when it is disposed. After an overflow, fine writes the backdrop, so a deferred presentation frame keeps the previous pixels. Each backend finds the retained scenes with ordered work through DrawingCommandBatch.FindOrderedScenes. The public API does not change. Tests cover each seal inside a layer on both backends, the gradient repetition, the scratch bounds, and a 100k-line offscreen render that overflows and chunks. The WebGPU reference images that held the old output are updated: the new WebGPU output equals the CPU output.
A plain WebGPU render now submits its work and returns. It reads no scratch status when every capacity is an upper bound of the GPU use. Ordered ranges, a binning bound above the binding limit, and chunked scenes without row bounds still read the status. At 100k lines the flush call takes about 45 ms against 97 ms on the baseline, and the time per frame is the same. The bounds are now true upper bounds: - The row bounds keep one entry for each tile row, so a chunk shorter than one bin gets the bound of its own rows. - The stroke style flags hold the CPU arc count, and the shader limits each round arc to it. - A long inner join adds its own crossing bound, and the inner miter uses the shader limit. - The PTCL bound comes from the chunk allocation in coarse. - Each clip estimate grows by one pixel on each side. - The outline radius of a Miter join is sqrt(m^2 + 1) half widths, which is the clipped bevel point of both strokers. - path_count makes the y clip exact, so each line adds at most its tile count and the row index stays in the bbox. A test renders 100k lines in chunks shorter than one bin and compares them with an unchunked render. The layer tests compare their pixels with the CPU backend.
The decode tests failed at random on Aztec symbols. The native ImageView of zxing-cpp keeps the pointer to the pixels, and BarcodeReader.Read reads through it later. The P/Invoke of the ImageView constructor pins the array only during that call, so a garbage collection between the two calls can move the array. The reader then reads other memory. ReadBarcodes pins the array with fixed until the read returns, and both decode call sites use it.
…tation The documentation said that the pen expands in local geometry space and that the outline is transformed after. Both backends stroke the transformed path in device space, with the pen width multiplied by the square root of the absolute determinant of the transform. The documentation now describes this behavior.
The documentation gives only the observable contract of the property: the transform that applies to vector output before rasterization.
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The CopyPixelsFromSelf case composites green 128 at 50% over white. The exact green value is 191.5, which is a rounding tie. The WebGPU backend on macOS gives 191, and the reference image has 192. The difference is 0.0184% in 96 pixels. The reference comparison of this case now uses 0.0185%, which is the measured difference plus one unit. The other cases keep 0.0003%.
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Prerequisites
Description
This PR corrects three faults in
DrawingCanvas. It also changes how the WebGPU backend sets the size of its scratch buffers.Calls inside a layer
A
Flush,RenderScene,CreateSceneorCopyPixelsFromcall betweenSaveLayerandRestorebroke the layer:Applycall lost its earlier content.Now these calls keep the layer whole on the two backends:
Flushdoes nothing while a layer is open.RenderScenedraws the scene into the open layer.CreateScenecloses the open layer at the end of the scene. Then the canvas opens the layer again.CopyPixelsFromreads the source rectangle and draws it into the open layer.Scenes in
CreateSceneCreateScenelost the scenes thatRenderScenerecorded before it. Now the new scene contains these scenes, in their recorded order.Gradient repetition
With
RepeatorReflect, a position before the start point got the color of the first stop. Now the two modes repeat the gradient in the two directions. The CPU backend and the WebGPU shaders use the same rule.WebGPU scratch buffers
The encoder calculates an upper bound for each scratch buffer. If all the bounds hold, a render submits its work and returns. It does not read back the scratch status.
A scene with ordered work, for example
Apply, still reads the status. If an offscreen render overflows a buffer, the backend renders the scene again with larger buffers.With 100,000 lines, the flush call takes approximately 45 ms. On
main, the same call takes 97 ms. The time for each frame does not change.The fine stage adds pixel coverage as fixed-point values. Thus, the order of the GPU work does not change the output.
Other changes
LineJoin.Miterstroke now include the clipped bevel point.DrawingOptions.Transformdocumentation no longer says that strokes expand in local space.The public API does not change. Some WebGPU reference images change. The new images match the CPU reference images.
Tests on Windows: net10.0 and net11.0 have 4414 passed, 0 failed and 9 skipped each.