bool
SharedFrameMetricsHelper::UpdateFromCompositorFrameMetrics(
ContainerLayer* aLayer,
bool aHasPendingNewThebesContent,
bool aLowPrecision,
ParentLayerRect& aCompositionBounds,
CSSToParentLayerScale& aZoom)
{
MOZ_ASSERT(aLayer);
CompositorChild* compositor = CompositorChild::Get();
if (!compositor) {
FindFallbackContentFrameMetrics(aLayer, aCompositionBounds, aZoom);
return false;
}
const FrameMetrics& contentMetrics = aLayer->GetFrameMetrics();
FrameMetrics compositorMetrics;
if (!compositor->LookupCompositorFrameMetrics(contentMetrics.mScrollId,
compositorMetrics)) {
FindFallbackContentFrameMetrics(aLayer, aCompositionBounds, aZoom);
return false;
}
aCompositionBounds = ParentLayerRect(compositorMetrics.mCompositionBounds);
aZoom = compositorMetrics.GetZoomToParent();
// Reset the checkerboard risk flag when switching to low precision
// rendering.
if (aLowPrecision && !mLastProgressiveUpdateWasLowPrecision) {
// Skip low precision rendering until we're at risk of checkerboarding.
if (!mProgressiveUpdateWasInDanger) {
return true;
}
mProgressiveUpdateWasInDanger = false;
}
mLastProgressiveUpdateWasLowPrecision = aLowPrecision;
// Always abort updates if the resolution has changed. There's no use
// in drawing at the incorrect resolution.
if (!FuzzyEquals(compositorMetrics.GetZoom().scale, contentMetrics.GetZoom().scale)) {
return true;
}
// Never abort drawing if we can't be sure we've sent a more recent
// display-port. If we abort updating when we shouldn't, we can end up
// with blank regions on the screen and we open up the risk of entering
// an endless updating cycle.
if (fabsf(contentMetrics.GetScrollOffset().x - compositorMetrics.GetScrollOffset().x) <= 2 &&
fabsf(contentMetrics.GetScrollOffset().y - compositorMetrics.GetScrollOffset().y) <= 2 &&
fabsf(contentMetrics.mDisplayPort.x - compositorMetrics.mDisplayPort.x) <= 2 &&
fabsf(contentMetrics.mDisplayPort.y - compositorMetrics.mDisplayPort.y) <= 2 &&
fabsf(contentMetrics.mDisplayPort.width - compositorMetrics.mDisplayPort.width) <= 2 &&
fabsf(contentMetrics.mDisplayPort.height - compositorMetrics.mDisplayPort.height)) {
return false;
}
// When not a low precision pass and the page is in danger of checker boarding
// abort update.
if (!aLowPrecision && !mProgressiveUpdateWasInDanger) {
if (AboutToCheckerboard(contentMetrics, compositorMetrics)) {
mProgressiveUpdateWasInDanger = true;
return true;
}
}
// Abort drawing stale low-precision content if there's a more recent
// display-port in the pipeline.
if (aLowPrecision && !aHasPendingNewThebesContent) {
return true;
}
return false;
}
