pull_request_summary.md

PR Summary: Fix Rendering Invalidation, Memory Leaks, and Add Compatibility Shims

This Pull Request introduces significant performance optimizations, architectural stability enhancements, and advanced vector/text composting features to the ProGPU graphics engine. It also adds three new compatibility shims (SkiaSharp, GDI+, and WPF DrawingContext) to allow drop-in replacement on the GPU.

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Key Achievements & Implementation Details

1. Deferred Native Resource Disposal & Memory Safety (Backend)

• Problem: Direct disposal of WebGPU handles (GpuTexture, GpuBuffer) on arbitrary garbage collection finalizer threads caused deadlocks or thread-unsafety crashes because WebGPU commands must run on the render thread.
• Solution: Implemented a thread-safe deferred disposal queue inside WgpuContext. Native handles are queued during garbage collection finalization, and the render loop thread safely drains and releases them synchronously during the frame render cycle. This resolved a memory leak of up to 28.6 GB under continuous redraw tests.
• Cleanup: Removed redundant/unsafe custom finalizers from managers like ComputeAccelerator and GlyphAtlas.

2. Precise Direction-Aware Winding Intersection Rules (Anti-Artifacting)

• Anti-Artifacting: Replaced standard winding interval calculations in GlyphRasterizerShader and PathRasterizerShader with Precise Direction-Aware Half-Open Winding Intervals to prevent dropout seams and horizontal line artifacts at curve/line boundaries:
  • Upward Crossing (deriv_y > 0.0): Evaluated on [0.0, 1.0) (inclusive of start, exclusive of end).
  • Downward Crossing (deriv_y < 0.0): Evaluated on (0.0, 1.0] (exclusive of start, inclusive of end).
• Optimization: Integrated a pipeline cache in RenderPipelineCache.cs to reuse compiled WebGPU shader pipelines and avoid compilation overhead.

3. Advanced Compositor & Scene Features

• Blending & Clipping: Implemented a blend mode stack, hierarchical geometry clipping masks, and opacity masks in Compositor.cs.
• Offscreen Texture Caching: Integrated offscreen texture caching to optimize rendering performance for nested visual layers and prevent redundant drawing of unchanged sub-trees.
• Winding Correction: Fixed boundary crossing mathematical logic within the Hatch shader to align with the precise winding rules.

4. Text & Vector Optimization

• Outline Caching: Added outline and Y-axis flipped outline caches (_glyphOutlineCache and _flippedOutlineCache) in TtfFont.cs to avoid parsing glyph geometries from TTF byte arrays multiple times.
• Glyph Flipping: Implemented GetFlippedGlyphOutline to flip coordinates along the Y-axis, conforming with WebGPU screen space coordinate projection.
• SVG Arc Support: Implemented SVG elliptical arc ('A'/'a') path segment parsing in PathGeometry.cs and compilation in PathAtlas.cs.

5. UI Controls & Hosting

• Corner Radius: Added CornerRadius support to ProGpuHostControl with rounded-rectangle clip path pushes in the Avalonia Render override.
• Context Reuse: Updated ProGpuHostControl to share the active WgpuContext instance.
• Type Safety: Refactored the UI composition communication to use a strongly-typed RenderState struct instead of a generic Tuple.

6. SkiaSharp Compat Shim API

• Drop-in Parity: Created a swappable baseline SkiaSharp API dependency mapping matching Avalonia's minimal rendering requirements (canvases, surfaces, typefaces, paints, paths, and text blobs).
• ReadPixels Support: Implemented native texture pixel readback (ReadPixels in GpuTexture.cs) utilizing asynchronous mapping to pull unpadded frame pixels back to the CPU cleanly.

7. GDI+ Compat Shim API (System.Drawing.Common)

• Graphics & Vectors: Implemented a swappable class library for GDI+ (System.Drawing.Common) mapping DrawLine, DrawRectangle, FillRectangle, DrawEllipse, FillEllipse, DrawPolygon, DrawPath, DrawString, MeasureString, and DrawImage directly onto the GPU command queue.
• Offscreen Bitmaps: Backed Bitmap and Image entirely by WebGPU texture targets. Drawing is accumulated on the GPU and read back only when requested.
• Diagnostics Preview: Created a visual page (GdiShowcasePage.cs) to showcase GDI drawings and operations in the gallery app.

8. WPF DrawingContext Compat Shim API (PresentationCore)

• WPF Parity: Added a swappable class library (PresentationCore) under the standard WPF namespaces (System.Windows, System.Windows.Media, System.Windows.Media.Imaging).
• Media Primitives: Maps standard primitives (DrawLine, DrawRectangle, DrawRoundedRectangle, DrawEllipse, DrawGeometry, DrawImage, DrawText, DrawGlyphRun) directly onto the GPU recorded command streams.
• State Stack: Manages a local transform matrix, opacity, and clipping geometry stack, resolving struct mutation writebacks for commands.
• Showcase Preview: Created an interactive page (WpfShowcasePage.cs) showing grid lines, StreamGeometry stars, transforms, opacities, and formatted text blocks.

9. GPU-Accelerated Path Geometry Operations (Layer 3)

• GPGPU Solver: Implemented 100% GPU-bound analytical path boolean solvers (Union, Intersect, Difference, XOR, Reverse Difference) without CPU curve flattening or triangulation.
• Anti-Artifacting & Precision Fixes: Resolved chord intersections near endpoints using boundary perturbation, relaxed endpoint containment intervals, and dynamic 16-step subdivision for curved chords.

10. High-Performance GPU-Accelerated Image Effects Engine

• Image Filters: Built a custom compositor pipeline to execute GPU-bound effects (e.g. Blur, Grayscale, Invert, Sepia, Brightness, Contrast) via customized shaders.
• Demo Gallery: Added an interactive UI page enabling users to tweak filter properties live and see the rendering performance.

11. Instanced Snapping & Subpixel Positioned Text Rendering

• Retina Snapping: Implemented physical pixel boundary snapping for glyph positions, eliminating font-rendering blurriness and improving readability at standard/retina DPI levels.

12. ShaderToy Playground & Live Compilation Engine

• WebGPU WGSL Engine: Created a custom compositor drawing extension ShaderToyExtensionPipeline (registered under IDrawingExtension.ShaderToy = 11) to execute custom fragment shaders backed by WebGPU.
• ShaderToy Compatibility: Created ShaderToyControl simulating the standard ShaderToy environment, supporting standard input uniforms (resolution iResolution, time iTime, frames iFrame, and mouse position iMouse).
• Interactive Editor UI: Built ShaderToyPlaygroundPage consisting of a live WebGPU canvas, Preset dropdown loaded with rich graphics presets (Cosmic Waves, Star Nest, Raymarched Torus SDF), real-time Timeline control, monospaced text editor, and a live compiler log diagnostics console.
• Panic Protection: Subscribed to static WgpuContext.OnWebGpuError events to catch shader compilation errors safely and skip pipeline creation when errors occur, preventing underlying WebGPU/Rust panics from aborting the host process.
• Headless Testing: Implemented headless unit tests to verify the ShaderToy Playground page and compilation pipeline under testing environments.

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Commit Log

1. cb10f7c backend: Implement deferred native resource disposal queue and finalizer safety
2. 81160dc backend: Implement precise direction-aware winding intersection rules and pipeline cache optimizations
3. f52bd12 scene: Add render commands for clipping, opacity masking, blend modes, and fix boundary crossings in Hatch shader
4. 0e5f6b6 compositor: Implement blend mode stack, geometry clipping masks, opacity masks, and offscreen texture caching
5. 3b860ea text: Implement glyph outline caching and coordinate flipping along Y-axis
6. cb67354 vector: Implement SVG elliptical arc path segment parsing and GPU compiler support
7. 3c424e2 cleanup: Remove redundant finalizers from compute accelerator and glyph atlas
8. 7d13f40 ui: Refactor ProGpuHostControl and fix WinUI Control template override
9. 64f724a shim: Implement SkiaSharp compatibility API and drawing context integration
10. 3bff12c vector: Implement GPU-accelerated analytical Path Boolean operations
11. a51c0e0 backend: Fix Path Ops rendering artifacts via boundary perturbation, endpoint relaxation, and dynamic chord steps
12. e84bea6 Improve text rendering performance and quality via instanced snapping and subpixel positioning
13. 8cd692a Implement high performance GPU-accelerated Image Effects Engine and demo page
14. fd7df1c Implement System.Drawing.Common (GDI+) shim library using ProGPU drawing context backend
15. 90bac10 samples: Add GDI Shim Showcase Page
16. a6f1c8e samples: Add Glyph Run Showcase Page
17. 4ae7378 backend: Fix shaders DPI scaling for text snapping and glyph rendering
18. 3f575b6 shim: Implement PresentationCore WPF DrawingContext compatibility shim
19. da76db2 samples: Add WPF DrawingContext Shim Showcase Page and register in MainWindow
20. 626bad1 tests: Add headless unit test verifying WPF Showcase Page rendering
21. 3c53832 docs: Update PR Summary with GDI+ and WPF DrawingContext shim details
22. 94cb793 Implement ShaderToyControl WinUI control for real-time WebGPU shader execution
23. cc7861b Add Text property to RichEditBox for raw string getting and setting
24. d7cc550 Implement ShaderToyPlaygroundPage gallery page with editor, preset selection, and error console
25. b0b0374 Integrate ShaderToy Playground page inside navigation drawer
26. a259b2e Relocate ShaderToyControl to ProGPU.Samples to resolve project circular dependencies
27. 66577ab Fix StackPanel ambiguity, ComboBox SelectedIndex, and Border properties in ShaderToyPlaygroundPage.cs
28. abd4e7f Add headless test verifying ShaderToy Playground page rendering
29. 1f44bcf Expose WebGPU compiler/validation error event and deferred render pipeline disposal helpers
30. b499186 Implement and register ShaderToyExtensionPipeline compositor backend for fragment shader rendering
31. 441a735 Remove IsTabStop from ShaderToyControl to fix FrameworkElement compilation
32. 5cd061c Fix StackOverflowException by removing redundant animation propagation loop in ShaderToyPlaygroundPage
33. 5534c20 Protect pipeline creation from compilation failures to prevent wgpu abort panics, and fix Preset 1 swizzling style