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Bug 1806026 part 2: Don't include the identity matrix when caching transforms for a11y. r=morgan

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See the code comments for details.
This is just a memory optimisation; there is no user visible change.

Differential Revision: https://phabricator.services.mozilla.com/D164996
This commit is contained in:
James Teh 2022-12-20 03:24:15 +00:00
parent 77088bfef9
commit 433e37a17f
2 changed files with 38 additions and 8 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

25
accessible/generic/LocalAccessible.cpp
View file

@ -3427,6 +3427,7 @@ already_AddRefed<AccAttributes> LocalAccessible::BundleFieldsForCache(
}
if (aCacheDomain & CacheDomain::TransformMatrix) {
bool transformed = false;
if (frame && frame->IsTransformed()) {
// We need to find a frame to make our transform relative to.
// It's important this frame have a corresponding accessible,
@ -3436,14 +3437,22 @@ already_AddRefed<AccAttributes> LocalAccessible::BundleFieldsForCache(
// This matrix is only valid when applied to CSSPixel points/rects
// in the coordinate space of `frame`. It also includes the translation
// to the parent space.
gfx::Matrix4x4 mtx = nsLayoutUtils::GetTransformToAncestor(
RelativeTo{frame}, RelativeTo{boundingFrame},
nsIFrame::IN_CSS_UNITS)
.GetMatrix();
UniquePtr<gfx::Matrix4x4> ptr = MakeUnique<gfx::Matrix4x4>(mtx);
fields->SetAttribute(nsGkAtoms::transform, std::move(ptr));
} else if (aUpdateType == CacheUpdateType::Update) {
gfx::Matrix4x4Flagged mtx = nsLayoutUtils::GetTransformToAncestor(
RelativeTo{frame}, RelativeTo{boundingFrame}, nsIFrame::IN_CSS_UNITS);
// We might get back the identity matrix. This can happen if there is no
// actual transform. For example, if an element has
// will-change: transform, nsIFrame::IsTransformed will return true, but
// this doesn't necessarily mean there is a transform right now.
// Applying the identity matrix is effectively a no-op, so there's no
// point caching it.
transformed = !mtx.IsIdentity();
if (transformed) {
UniquePtr<gfx::Matrix4x4> ptr =
MakeUnique<gfx::Matrix4x4>(mtx.GetMatrix());
fields->SetAttribute(nsGkAtoms::transform, std::move(ptr));
}
}
if (!transformed && aUpdateType == CacheUpdateType::Update) {
// Otherwise, if we're bundling a transform update but this
// frame isn't transformed (or doesn't exist), we need
// to send a DeleteEntry() to remove any

21
accessible/tests/browser/bounds/browser_test_simple_transform.js
View file

@ -88,6 +88,27 @@ addAccessibleTask(
</div>
`,
async function(browser, docAcc) {
if (isCacheEnabled) {
// Even though willChangeTop has no transform, it has
// will-change: transform, which means nsIFrame::IsTransformed returns
// true. We don't cache identity matrices, but because there is an offset
// to the root frame, layout includes this in the returned transform
// matrix. That means we get a non-identity matrix and thus we cache it.
// This is why we only test the identity matrix cache optimization for
// willChangeInner.
let hasTransform;
try {
const willChangeInner = findAccessibleChildByID(
docAcc,
"willChangeInner"
);
willChangeInner.cache.getStringProperty("transform");
hasTransform = true;
} catch (e) {
hasTransform = false;
}
ok(!hasTransform, "willChangeInner has no cached transform");
}
await testBoundsWithContent(docAcc, "willChangeTopP2", browser);
await testBoundsWithContent(docAcc, "willChangeInnerP2", browser);
},