Viz: Chrome Graphics Futures

Tokyo, 2017/09/21

About this talk

• If you were here at the last BlinkOn...
• I talked about Mus and Compositing
• We've refined our plans and made some progress since then.
• So an update.

Viz: Two contexualizations

• Servicification
  • The Mojo UI service is a core service in Chrome
  • Viz (for Visuals) is a sub-service responsible for producing visual output: compositing, rasterization, GPU virtualization.
• Augmenting the GPU Process
  • In existing Chrome, the GPU process is responsible for virtualizing a hardware GPU.
  • But we are adding additional functionality for compositing and rasterization.
  • So a new name.

Servicified Chrome Viz Context

GPU process vs Viz

• Viz is more than just a servicification tickbox.
• Viz is also about making Chrome graphics better for the Web platform:
  • Better compositing performance
  • Better rasterization performance
  • Toll-free rasterization and compositing for site isolation

Current WebPlatform Graphics Pipeline

Viz Tadpole

• Coming to Chrome over the next 2-3 milestones
• A prepatory refactoring for direct compositing: removing the bolded CommandBuffer
• Promises to deliver a 10-15% performance improvement

Viz Tadpole with Direct Skia Compositing

• Tadpole DisplayCompositor uses GLRenderer
• Replace with SkiaRenderer for direct compositing
• Enable the WIP version --use-skia-renderer

Aside: Why is Tadpole Hard?

• Tadpole is conceptually simple for the web platform
• The before and after picture for renderer processes is unchanged:
• Only have to alter the setup of CompositorFrame transport
• But Tadpole also requires many browser-side changes

UI Graphics Pipeline Changes

• Synchronous function call before
• Asynchronous IPC after:

Tadpole Status (crbug/601863)

• Surface References to improve tracking of objects on in 63
• Improved CompositorFrame eviction on in 64
• Surface Synchronization so UI can atomically update sizes of web platform children on in 64
• Cross-process Tab readback on in 64
• Revised event targeting on in 64
• Improved occlusion culling on in 64
• SkiaRenderer performant in 67

Parallel Effort: OOP Rasterization

• Centralizing the display compositor permits reducing command buffer overhead
• So does delegating serialized paint ops to Viz for Out Of Process rasterization
• Partial implementation behind flag: --enable-gpu-rasterization
--enable-oop-rasterization

OOP Rasterization

• Now: each web platform client generates GL
• Next: OOP rasterization serializes paint ops and rasterizes in Viz

Combined Tadpole and OOP Rasterization

• Note absence of GL command buffers
• Improves both raster and compositing performance

Enabling Vulkan

• Vulkan API is not ammenable to implementing a command buffer
• Skia has a Vulkan backend
• Vulkan promises 10-15% better performance beyond the GL implementation for both SkiaRenderer and paint op rasterization

Aside: WebGL Requires CommandBuffer

• A platform-specific API could permit texture sharing with Native GL
• Angle for Vulkan (aka Vangle) would permit direct interop

Explaining the Site Isolation Graphics Toll

• Site isolation improves security
• With site-isolation, a single top-level page like this:
• Unnecessarily allocates GPU memory and rasterizes the red region:

Now: Aggregation After Rasterization

• Makes rasterization decisions locally in the renderers
• So rasterize everything that might be needed
• Display Compositor aggregates the contributed layers
• Result: redundant rasterization

Salamander: Aggregation Before Raster

• Start with same paint ops
• Add layerization data from property trees
• Aggregate centrally
• Rasterize and composite the smallest necessary set of paint ops

Summary: Viz Status

• Underway now
  • Tadpole: relocate the DisplayCompositor to Viz in 66
  • OOP Rasterization in Viz Q2 2018
  • SkiaRenderer in 67
• After the above starting Q3 2018
  • Vulkan graphics
  • Salamander: central layerization

Viz Take-aways

• Two ways to think about Viz:
  • Servicification of graphics in Chrome
  • A better GPU process
• Viz improves webplatform graphics three ways:
  • 10-15% performance benefit from removing command buffers
  • Vulkan support for another 10-15% performance benefit
  • Central aggregation for toll-free site-isolation support