1458302 - Use nsDisplayItem::IsReused as a preliminary check to figure out if nsDisplayTransform's transform has changed

Status: NEW

(Core :: Graphics: WebRender, enhancement, P3)

Description

[Matt Woodrow (:mattwoodrow)]

If IsReused is false, then the item is the same one as was used last time (retained by retained-dl), and the transform must not have changed.

WR is currently comparing transforms, so we could use this to reduce how often we have to do the full matrix compare.

Comment 1

[Markus Stange [:mstange]]

The transform comparison happens at https://searchfox.org/mozilla-central/rev/8837610b6c999451435695e800f38d4acbc0a644/gfx/layers/wr/WebRenderCommandBuilder.cpp#268

Comment 2

[Jeff Muizelaar [:jrmuizel]]

I don't think we need this for release.

Comment 3

[Nicolas Silva [:nical]]

It looks like the code that does the full matrix compare doesn't exist anymore, (and by the look of it the new code is https://searchfox.org/mozilla-central/rev/6cc48251bb97600fdf11a5b4c5f621bfc8606d55/gfx/layers/wr/WebRenderCommandBuilder.cpp#263 ).

There is still https://searchfox.org/mozilla-central/rev/6cc48251bb97600fdf11a5b4c5f621bfc8606d55/gfx/layers/wr/WebRenderCommandBuilder.cpp#484 which already existed when this bug was filed.

Should we close this bug?

Comment 4

[Matt Woodrow (:mattwoodrow)]

It looks like the code to skip invalidation checks if we have a retained display item are disabled - https://searchfox.org/mozilla-central/rev/6cc48251bb97600fdf11a5b4c5f621bfc8606d55/gfx/layers/wr/WebRenderCommandBuilder.cpp#383