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Bug 1340282 - Update docs on how to create a new webrender display item. r=gfx? DONTBUILD

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Mason Chang 2017-02-16 12:53:13 -08:00
parent 0c0ade836a
commit 0652b603be
1 changed files with 14 additions and 13 deletions
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gfx/doc/README.displayitem
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@ -7,21 +7,22 @@ How to add a new WebRender display item from a Gecko Display item, the general f
More detailed steps are:
1) Force layout to create an active layer for the gecko display item.
See http://searchfox.org/mozilla-central/rev/0f254a30d684796bcc8b6e2a102a0095d25842bb/layout/generic/nsTextFrame.cpp#4983
as an example for text layers. Ping Matt Woodrow or Markus Stange for help.
See http://searchfox.org/mozilla-central/source/layout/painting/nsDisplayList.h#1850
The Active layer part comes from nsDisplayText::GetLayerState
For most items, we should just be creating a DisplayItemLayer. The DisplayItemLayer has a pointer to the nsDisplayItem. To layerize, just return an active layer for the current item.
2) Create the new display item layer:
See https://hg.mozilla.org/projects/graphics/file/c8873c351679e4a394170cd899e8b5a5fb2a00e7/layout/painting/nsDisplayList.cpp#l4403
See text layer:
http://searchfox.org/mozilla-central/rev/0f254a30d684796bcc8b6e2a102a0095d25842bb/gfx/layers/Layers.h#2403
Thus for most display items, it's just implementing:
GetLayerState,
BuildLayer (which should just call BuildDisplayItemLayer)
CreateWebRenderCommands.
The layer should have all the information to display the item.
2) When implementing CreateWebRenderCommands, take a look at the nsDisplayItem::Paint method and reproduce the logic in webrender display items.
3) Create the WebRender equivalent layer. In YourLayerType::RenderLayer, serialize the data needed for the layer type.
4) If you need to add a custom IPC serialization mechanism, do it in WebRenderMessageUtils.h
5) Create a WebRender command to process the new layer type in WebRenderMessages.ipdlh. These are the struct OpDPPushYourLayerTypeHere
6) Add a new function in WebRender.h that will call out into webrender to render your display item.
7) In WebRenderBridgeParent::ProcessWebRenderCommands, call out to the new function in (6).
8) Fill out the function in (6) in bindings.rs to make webrender do the right thing. Generally, it's just push a display item.
If you need to implement a new WebRender display item (generally shouldn't be needed):
1) If you need to pipe in a new WR display item type, do it in WebRenderMessages.ipdl.
2) If you need to add a custom IPC serialization mechanism, do it in WebRenderMessageUtils.h
3) Add a new function in WebRender.h that will call out into webrender for a new WR display item.
4) In WebRenderBridgeParent::ProcessWebRenderCommands, call out to the new function in (3).
5) Fill out the function in (3) in bindings.rs to make webrender do the right thing.