[Webkit-unassigned] [Bug 101023] New: Coordinated Graphics: CoordinatedGraphicsLayer handles a composited image with TiledBackingStore.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=101023

           Summary: Coordinated Graphics: CoordinatedGraphicsLayer handles
                    a composited image with TiledBackingStore.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: luxtella at company100.net


Currently, Coordinated Graphics has several problems in terms of handling a composited image.
1. We can not send an image to UI Process using GraphicsSurface, because GraphicsSurface has the size limitation.(GL_MAX_TEXTURE_SIZE)
2. CoordinatedGraphicsLayer, LayerTreeCoordinator, LayerTreeCoordinatorProxy and LayerTreeRenderer are tightly coupled to share an image using ShareableBitmap.
3. LayerTreeCoordinator needs platform dependent code to copy an image to ShareableBitmap.
4. We must allocate big continuous memory when an image is big.
5. Even if a composited image is off the viewport, TextureMapperLayer can not remove an image texture.

If we use TiledBackingStore to handle a composited image, we can get following benefits.
1. We can use GraphicsSurface to send an image to UI Process.
2. We can remove huge complex code to handle IPC for an image and just reuse existing TiledBackingStore.
3. LayerTreeCoordinator does not need platform dependent code.
4. We can send a big image to UI Process using many small tiles.
5. When a composited image is off the viewport, TextureMapperLayer can remove an image texture to save texture memory.

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