Instead, schedule a delayed composite after each frame of an animation.
The previous code would cause jank, because the following sequence
frequently occurred:
1. The page uses `requestAnimationFrame()` to request a frame.
2. The compositor receives the message, schedules a composite,
dispatches the rAF message to the script thread, composites, and goes to
sleep waiting for vblank (frame 1).
3. The script makes a change and sends it through the pipeline.
Eventually it gets painted and is sent to the compositor, but the
compositor is sleeping.
4. The compositor wakes up, sees the new painted content, page flips,
and goes to sleep (frame 2). Repeat from step 1.
The problem is that we have two composition frames, not just one. This
halves Web apps' framerate!
This commit fixes the problem by scheduling the composite in step 2 to
12 ms in the future. We already have this delayed-composition
functionality in the form of the scrolling timer, which I repurposed and
renamed to the "delayed composition timer" for this task. This change
gives the page 12 ms to prepare the frame, which seems to usually be
enough, especially with WebRender.
Note that simply removing the scheduled composite after rAF is not the
correct solution. If this is done, then pages that call rAF and don't
modify the page won't receive future rAFs, since the compositor will be
sleeping and won't be notified of vblank.
Fixes a bunch of jank in browser.html. The remaining jank seems to be a
problem with browser.html itself.
WebRender is an experimental GPU accelerated rendering backend for Servo.
The WebRender backend can be specified by running Servo with the -w option (otherwise the default rendering backend will be used).
WebRender has many bugs, and missing features - but it is usable to browse most websites - please report any WebRender specific rendering bugs you encounter!
Fixes additional calls to rAF.
Often, a rAF callback will request another rAF from the callback itself.
Previously, the constellation would quickly receive two messages saying
that there were no animations, and then there are animations again in the
situation above. This would make the compositor tick the new animation straight
away, causing strange fluctuations and timings in rAF callbacks.
Instead, only send the NoAnimationCallbacks message if the animation
callback queue is still empty after invoking the callbacks.
This fixes rAF timing, which now runs at the correct (vsync) framerate.
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after navigation.
The first bug was that iframes were not reflowed in their parent DOM
when the child page navigated. This is fixed by simply having the
constellation notify the appropriate script thread when navigation
occurs.
The second bug was that the compositor was unable to adjust the pipeline
for existing iframe layers, only new ones. This patch adds logic to do
that.
Closes#8081.
