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Bug 1209697: Cache flex measuring reflows to avoid exponential behavior

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This commit is contained in:
janekptacijarabaci 2018-04-24 20:18:05 +02:00 • committed by Roy Tam
commit 95b1132e04
2 changed files with 114 additions and 39 deletions
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138
layout/generic/nsFlexContainerFrame.cpp
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@ -33,6 +33,8 @@ typedef nsFlexContainerFrame::FlexItem FlexItem;
typedef nsFlexContainerFrame::FlexLine FlexLine;
typedef nsFlexContainerFrame::FlexboxAxisTracker FlexboxAxisTracker;
typedef nsFlexContainerFrame::StrutInfo StrutInfo;
typedef nsFlexContainerFrame::CachedMeasuringReflowResult
CachedMeasuringReflowResult;
static mozilla::LazyLogModule gFlexContainerLog("nsFlexContainerFrame");
@ -1756,6 +1758,91 @@ nsFlexContainerFrame::
}
}
/**
* A cached result for a measuring reflow.
*
* Right now we only need to cache the available size, the height and the
* ascent. This can be extended later if needed.
*
* The assumption here is that a given flex item measurement won't change until
* either the available size changes, or the flex container intrinsic size is
* marked as dirty (due to a style or DOM change).
*
* Caching it prevents us from doing exponential reflows in cases of deeply
* nested flex and scroll frames.
*
* We store them in the frame property table for simplicity.
*/
struct nsFlexContainerFrame::CachedMeasuringReflowResult
{
LogicalSize mAvailableSize;
const nscoord mHeight;
const nscoord mAscent;
CachedMeasuringReflowResult(const LogicalSize& aAvailableSize,
nscoord aHeight,
nscoord aAscent)
: mAvailableSize(aAvailableSize)
, mHeight(aHeight)
, mAscent(aAscent)
{}
};
NS_DECLARE_FRAME_PROPERTY_DELETABLE(CachedFlexMeasuringReflow,
CachedMeasuringReflowResult);
const CachedMeasuringReflowResult&
nsFlexContainerFrame::MeasureAscentAndHeightForFlexItem(
FlexItem& aItem,
nsPresContext* aPresContext,
ReflowInput& aChildReflowInput)
{
const auto availableSize = aChildReflowInput.AvailableSize();
const FrameProperties props = aItem.Frame()->Properties();
if (const auto* cachedResult = props.Get(CachedFlexMeasuringReflow())) {
if (cachedResult->mAvailableSize == availableSize) {
return *cachedResult;
}
}
ReflowOutput childDesiredSize(aChildReflowInput);
nsReflowStatus childReflowStatus;
const uint32_t flags = NS_FRAME_NO_MOVE_FRAME;
ReflowChild(aItem.Frame(), aPresContext,
childDesiredSize, aChildReflowInput,
0, 0, flags, childReflowStatus);
aItem.SetHadMeasuringReflow();
// XXXdholbert Once we do pagination / splitting, we'll need to actually
// handle incomplete childReflowStatuses. But for now, we give our kids
// unconstrained available height, which means they should always complete.
MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
"We gave flex item unconstrained available height, so it "
"should be complete");
// Tell the child we're done with its initial reflow.
// (Necessary for e.g. GetBaseline() to work below w/out asserting)
FinishReflowChild(aItem.Frame(), aPresContext,
childDesiredSize, &aChildReflowInput, 0, 0, flags);
auto result =
new CachedMeasuringReflowResult(availableSize,
childDesiredSize.Height(),
childDesiredSize.BlockStartAscent());
props.Set(CachedFlexMeasuringReflow(), result);
return *result;
}
/* virtual */ void
nsFlexContainerFrame::MarkIntrinsicISizesDirty()
{
for (nsIFrame* childFrame : mFrames) {
childFrame->Properties().Delete(CachedFlexMeasuringReflow());
}
}
nscoord
nsFlexContainerFrame::
MeasureFlexItemContentHeight(nsPresContext* aPresContext,
@ -1783,27 +1870,15 @@ nsFlexContainerFrame::
childRIForMeasuringHeight.SetVResize(true);
}
ReflowOutput childDesiredSize(childRIForMeasuringHeight);
nsReflowStatus childReflowStatus;
const uint32_t flags = NS_FRAME_NO_MOVE_FRAME;
ReflowChild(aFlexItem.Frame(), aPresContext,
childDesiredSize, childRIForMeasuringHeight,
0, 0, flags, childReflowStatus);
const CachedMeasuringReflowResult& reflowResult =
MeasureAscentAndHeightForFlexItem(aFlexItem, aPresContext,
childRIForMeasuringHeight);
MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
"We gave flex item unconstrained available height, so it "
"should be complete");
FinishReflowChild(aFlexItem.Frame(), aPresContext,
childDesiredSize, &childRIForMeasuringHeight,
0, 0, flags);
aFlexItem.SetHadMeasuringReflow();
aFlexItem.SetAscent(childDesiredSize.BlockStartAscent());
aFlexItem.SetAscent(reflowResult.mAscent);
// Subtract border/padding in vertical axis, to get _just_
// the effective computed value of the "height" property.
nscoord childDesiredHeight = childDesiredSize.Height() -
nscoord childDesiredHeight = reflowResult.mHeight -
childRIForMeasuringHeight.ComputedPhysicalBorderPadding().TopBottom();
return std::max(0, childDesiredHeight);
@ -3959,25 +4034,10 @@ nsFlexContainerFrame::SizeItemInCrossAxis(
// whether any of its ancestors are being resized).
aChildReflowInput.SetVResize(true);
}
ReflowOutput childDesiredSize(aChildReflowInput);
nsReflowStatus childReflowStatus;
const uint32_t flags = NS_FRAME_NO_MOVE_FRAME;
ReflowChild(aItem.Frame(), aPresContext,
childDesiredSize, aChildReflowInput,
0, 0, flags, childReflowStatus);
aItem.SetHadMeasuringReflow();
// XXXdholbert Once we do pagination / splitting, we'll need to actually
// handle incomplete childReflowStatuses. But for now, we give our kids
// unconstrained available height, which means they should always complete.
MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
"We gave flex item unconstrained available height, so it "
"should be complete");
// Tell the child we're done with its initial reflow.
// (Necessary for e.g. GetBaseline() to work below w/out asserting)
FinishReflowChild(aItem.Frame(), aPresContext,
childDesiredSize, &aChildReflowInput, 0, 0, flags);
// Potentially reflow the item, and get the sizing info.
const CachedMeasuringReflowResult& reflowResult =
MeasureAscentAndHeightForFlexItem(aItem, aPresContext, aChildReflowInput);
// Save the sizing info that we learned from this reflow
// -----------------------------------------------------
@ -3989,7 +4049,7 @@ nsFlexContainerFrame::SizeItemInCrossAxis(
// so we don't bother with making aAxisTracker pick the cross-axis component
// for us.)
nscoord crossAxisBorderPadding = aItem.GetBorderPadding().TopBottom();
if (childDesiredSize.Height() < crossAxisBorderPadding) {
if (reflowResult.mHeight < crossAxisBorderPadding) {
// Child's requested size isn't large enough for its border/padding!
// This is OK for the trivial nsFrame::Reflow() impl, but other frame
// classes should know better. So, if we get here, the child had better be
@ -4002,10 +4062,10 @@ nsFlexContainerFrame::SizeItemInCrossAxis(
aItem.SetCrossSize(0);
} else {
// (normal case)
aItem.SetCrossSize(childDesiredSize.Height() - crossAxisBorderPadding);
aItem.SetCrossSize(reflowResult.mHeight - crossAxisBorderPadding);
}
aItem.SetAscent(childDesiredSize.BlockStartAscent());
aItem.SetAscent(reflowResult.mAscent);
}
void
@ -4295,7 +4355,7 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext* aPresContext,
LogicalSize availSize = aReflowInput.ComputedSize(wm);
availSize.BSize(wm) = NS_UNCONSTRAINEDSIZE;
ReflowInput childReflowInput(aPresContext, aReflowInput,
item->Frame(), availSize);
item->Frame(), availSize);
if (!sizeOverride) {
// Directly override the computed main-size, by tweaking reflow state:
if (aAxisTracker.IsMainAxisHorizontal()) {