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| 1 # cc/ | 1 # cc/ | 
| 2 | 2 | 
| 3 This directory contains a compositor, used in both the renderer and the | 3 This directory contains a compositor, used in both the renderer and the | 
| 4 browser.  In the renderer, Blink is the client.  In the browser, both | 4 browser.  In the renderer, Blink is the client.  In the browser, both | 
| 5 ui and Android browser compositor are the clients. | 5 ui and Android browser compositor are the clients. | 
| 6 | 6 | 
| 7 The public API of the compositor is LayerTreeHost and Layer and its | 7 The public API of the compositor is LayerTreeHost and Layer and its | 
| 8 derived types.  Embedders create a LayerTreeHost (single, multithreaded, | 8 derived types.  Embedders create a LayerTreeHost (single, multithreaded, | 
| 9 or synchronous) and then attach a tree of Layers to it. | 9 or synchronous) and then attach a tree of Layers to it. | 
| 10 | 10 | 
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| 86 ### LayerTree | 86 ### LayerTree | 
| 87 | 87 | 
| 88 ### Occlusion Culling | 88 ### Occlusion Culling | 
| 89 Avoiding work by skipping over things which are not visible due to being | 89 Avoiding work by skipping over things which are not visible due to being | 
| 90 occluded (hidden from sight by other opaque things in front of them). Most | 90 occluded (hidden from sight by other opaque things in front of them). Most | 
| 91 commonly refers to skipping drawing (ie culling) of DrawQuads when other | 91 commonly refers to skipping drawing (ie culling) of DrawQuads when other | 
| 92 DrawQuads will be in front and occluding them. | 92 DrawQuads will be in front and occluding them. | 
| 93 | 93 | 
| 94 ### Property Trees | 94 ### Property Trees | 
| 95 | 95 | 
|  | 96 See also presentations on [Compositor Property Trees](https://docs.google.com/pr
     esentation/d/1V7gCqKR-edNdRDv0bDnJa_uEs6iARAU2h5WhgxHyejQ/preview) | 
|  | 97 and [Blink Property Trees](https://docs.google.com/presentation/u/1/d/1ak7YVrJIT
     GXxqQ7tyRbwOuXB1dsLJlfpgC4wP7lykeo/preview). | 
|  | 98 | 
| 96 ### Display | 99 ### Display | 
| 97 A controller class that takes CompositorFrames for each surface and draws them | 100 A controller class that takes CompositorFrames for each surface and draws them | 
| 98 to a physical output. | 101 to a physical output. | 
| 99 | 102 | 
| 100 ### Draw | 103 ### Draw | 
| 101 Filling pixels in a physical output (technically could be to an offscreen | 104 Filling pixels in a physical output (technically could be to an offscreen | 
| 102 texture), but this is the final output of the display compositor. | 105 texture), but this is the final output of the display compositor. | 
| 103 | 106 | 
| 104 ### DrawQuad | 107 ### DrawQuad | 
| 105 A unit of work for drawing. Each DrawQuad has its own texture id, transform, | 108 A unit of work for drawing. Each DrawQuad has its own texture id, transform, | 
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| 187 system that converts painting (raster sources / recording sources) into | 190 system that converts painting (raster sources / recording sources) into | 
| 188 rasterized resources that live on tiles. This also kicks off any dependent image | 191 rasterized resources that live on tiles. This also kicks off any dependent image | 
| 189 decodes for images that need to be decode for the raster to take place. | 192 decodes for images that need to be decode for the raster to take place. | 
| 190 | 193 | 
| 191 ### Device Scale Factor | 194 ### Device Scale Factor | 
| 192 The scale at which we want to display content on the output device. For very | 195 The scale at which we want to display content on the output device. For very | 
| 193 high resolution monitors, everything would become too small if just presented | 196 high resolution monitors, everything would become too small if just presented | 
| 194 1:1 with the pixels. So we use a larger number of physical pixels per logical | 197 1:1 with the pixels. So we use a larger number of physical pixels per logical | 
| 195 pixels. This ratio is the device scale factor. 1 or 2 is the most common on | 198 pixels. This ratio is the device scale factor. 1 or 2 is the most common on | 
| 196 ChromeOS. Values between 1 and 2 are common on Windows. | 199 ChromeOS. Values between 1 and 2 are common on Windows. | 
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