wr2 metabug

[glennw]

A list of things we need to handle for wr2. Some of these are blockers for merging, but many can be left until after that.

Blockers

• Tidy up the shaders directory - remove unused shaders - 50% done
• 3d transforms - 50% done
• Image stretch size support - mchang working on.
• Angle gradient support - WIP branch - nearly done.
• Box shadow caching
• Non-rectangular clip support - gw working on.
• Tidy up size of UBO array lengths, based on GPU capabilities
• Support other border styles
• Support irregular border corner radii
• Integrate the other mix-blend-mode / filter shaders.
• Re-add webgl display item support.
• transform issue with b.html sidebar.
• pixel snapping.
• accuracy bug with angle gradients.
• square corners on GH bug (gradient clip?).
• box shadow bug on GH (box shadow clip?).

Optimization ideas

• Avoid packing primitives for multiple tiles
• Run parts of tiling / packing / batching on worker threads
• Optimize / improve the batching algorithm for the alpha batching strategy
• Add support for partial tile allocations - optimization for transparent_rects
• Add support for simple rectangle paths - minimize allocation size
• Support narrowphase detection during tile assignment - optimization for moire demo
• Support intra-layer occlusion tests - general optimization
• Support splitting large rounded rectangles - potential general optimization
• Consider storing all packed primitives in same structure - potential optimization / simpler code
• Add support for > 8 blend layers per tile - automate the shader code gen?
• Support narrow phase tile collision test for 3d transformed / perspective layers.

Others

• Anti-aliasing - mrobinson is prototyping this.
• PoC fast path rendering strategy (suggest background color + text tiles)
• Re-enable rasterizing glyphs on worker threads
• Add more fine grained GPU timer queries - to profile various parts of each frame.

[changm]

My list, not sure this should be a blocker for wr2 merging, or it might be categorized as "before we decide on wr for gecko".

• An evaluation of WR on Windows.
• A better story for non good GPUs
• Standalone WR tests outside of Servo (I can permacrash today with a simple html page that has a background image).

[glennw]

@changm For the non-good GPUs, I'd like to try running WR on top of https://blog.chromium.org/2016/06/universal-rendering-with-swiftshader.html and see what the performance is like.

[glennw]

wr2 landed! We can open separate bugs for the remaining optimization work above.