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![Daniel van Vugt](/assets/img/avatar_default.png)
We were setting the pipeline colour to all white (1.0, 1.0, 1.0, 1.0) and so the default layer combine function multiplied each pixel (R, G, B, A) by all ones. Obviously multiplying by one four times per pixel is a waste of effort so we remove the colour setting *and* set the layer combine function to a trivial shader that will ignore whatever the current pipeline colour is set to. So now we do **zero** multiplies per pixel. On an i7-7700 at UHD 3840x2160 this results in 5% faster render times and 10% lower power usage (says intel_gpu_top). The benefit is probably much higher for virtual machines though, as they're no longer being asked to do CPU-based math on every pixel of a window. https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1331
Intro ===== In general, the compositor splits the window from the contents of the window from the shape of the window. In other words, a window has contents, and the contents of the window have a shape. This is represented by the actor hierarchy: +--------------------------------------+ | MetaWindowActor | | +----------------------------------+ | | | MetaSurfaceActor | | | | +------------------------------+ | | | | | MetaShapedTexture | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +------------------------------+ | | | +----------------------------------+ | +--------------------------------------+ Surfaces may also contain subsurfaces. The MetaWindowActor and MetaSurfaceActor subclasses that will be created depend on the client type, and the display server type. ## Subsurfaces Additionally, there is also the case of subsurfaces: surfaces that are child of other surfaces. That is also represented in the actor hierarchy by having one or many MetaSurfaceActors (the subsurfaces) added as children of a parent MetaSurfaceActor. There are no limits to how many subsurfaces a surface may have. With subsurfaces, the actor hierarchy looks like this: MetaWindowActor ↳ MetaSurfaceActor (surface) ↳ MetaShapedTexture ↳ MetaSurfaceActor (subsurface) ↳ MetaShapedTexture ↳ MetaSurfaceActor (sub-subsurface) ↳ MetaShapedTexture ↳ MetaSurfaceActor (subsurface) ↳ MetaShapedTexture In this example, the main surface has 2 subsurfaces. One of these subsurfaces contains a subsurface as well. All MetaWindowActors contain at least one MetaSurfaceActor, and all MetaSurfaceActors contain a MetaShapedTexture. ## Client and compositor MetaWindowActor and its subclasses represent the client window's type. A X11 client will have a MetaWindowActorX11 representing it, and a Wayland client will have a MetaWindowActorWayland. On the compositor side, the surface where the contents of the window are drawn into are represented by MetaSurfaceActor subclasses. On a Wayland session, windows are backed by a MetaSurfaceActorWayland surface, whereas on X11 sessions, by MetaSurfaceActorX11. XWayland windows are X11 client windows (MetaWindowActorX11) backed by Wayland surfaces (MetaWindowActorWayland). Env Vars ======== MUTTER_DISABLE_MIPMAPS - set to disable use of mipmaped windows.