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Commit bd27a728 authored by David Bokan's avatar David Bokan Committed by Commit Bot
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Don't promote implicit root scroller with multiple matches 

chrishtr@ pointed out in https://crrev.com/c/1038648 that the paint
order selection used when multiple elements on a page meet all the
criteria of an implicit root scroller isn't correct.

On reflection, it's not immediately clear to me that this is at all
useful so, rather than adding complexity, this CL removes the ordering
and just avoids making any decision at all in this case. We can revisit
if the need comes up in real usage.

Bug: 844534
Change-Id: I4e05da981eace4062f3898a3a7fe1d4cffdec658
Reviewed-on: https://chromium-review.googlesource.com/c/1288905Reviewed-by: default avatarChris Harrelson <chrishtr@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601161}
parent 0d2b1013
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Showing with 61 additions and 18 deletions
third_party/blink/renderer/core/page/scrolling/root_scroller_controller.cc
View file @ bd27a728
...@@ -393,8 +393,7 @@ void RootScrollerController::ProcessImplicitCandidates() { ...@@ -393,8 +393,7 @@ void RootScrollerController::ProcessImplicitCandidates() {
if (ScrollsVerticalOverflow(*document_->GetLayoutView())) if (ScrollsVerticalOverflow(*document_->GetLayoutView()))
return; return;
Element* highest_z_element = nullptr; bool multiple_matches = false;
bool highest_is_ambiguous = false;
HeapHashSet<WeakMember<Element>> copy(implicit_candidates_); HeapHashSet<WeakMember<Element>> copy(implicit_candidates_);
for (auto& element : copy) { for (auto& element : copy) {
...@@ -404,25 +403,15 @@ void RootScrollerController::ProcessImplicitCandidates() { ...@@ -404,25 +403,15 @@ void RootScrollerController::ProcessImplicitCandidates() {
continue; continue;
} }
if (!highest_z_element) { if (implicit_root_scroller_)
highest_z_element = element; multiple_matches = true;
} else {
int element_z = element->GetLayoutObject()->Style()->ZIndex(); implicit_root_scroller_ = element;
int highest_z = highest_z_element->GetLayoutObject()->Style()->ZIndex();
if (element_z > highest_z) {
highest_z_element = element;
highest_is_ambiguous = false;
} else if (element_z == highest_z) {
highest_is_ambiguous = true;
}
}
} }
if (highest_is_ambiguous) // Only promote an implicit root scroller if we have a unique match.
if (multiple_matches)
implicit_root_scroller_ = nullptr; implicit_root_scroller_ = nullptr;
else
implicit_root_scroller_ = highest_z_element;
} }
PaintLayer* RootScrollerController::RootScrollerPaintLayer() const { PaintLayer* RootScrollerController::RootScrollerPaintLayer() const {
......
third_party/blink/renderer/core/page/scrolling/root_scroller_test.cc
View file @ bd27a728
...@@ -1937,6 +1937,60 @@ TEST_F(ImplicitRootScrollerSimTest, ImplicitRootScrollerIframe) { ...@@ -1937,6 +1937,60 @@ TEST_F(ImplicitRootScrollerSimTest, ImplicitRootScrollerIframe) {
GetDocument().GetRootScrollerController().EffectiveRootScroller()); GetDocument().GetRootScrollerController().EffectiveRootScroller());
} }
// Tests that if we have multiple valid candidates for implicit promotion, we
// don't promote either.
TEST_F(ImplicitRootScrollerSimTest, DontPromoteWhenMultipleAreValid) {
WebView().Resize(WebSize(800, 600));
SimRequest request("https://example.com/test.html", "text/html");
LoadURL("https://example.com/test.html");
request.Complete(R"HTML(
<!DOCTYPE html>
<style>
::-webkit-scrollbar {
width: 0px;
height: 0px;
}
body, html {
width: 100%;
height: 100%;
margin: 0px;
}
iframe {
position: absolute;
left: 0;
top: 0;
width: 100%;
height: 100%;
border: 0;
}
</style>
<iframe id="container"
srcdoc="<!DOCTYPE html><style>html {height: 300%;}</style>">
</iframe>
<iframe id="container2"
srcdoc="<!DOCTYPE html><style>html {height: 300%;}</style>">
</iframe>
)HTML");
// srcdoc iframe loads via posted tasks.
RunPendingTasks();
Compositor().BeginFrame();
// Since both iframes are valid candidates, neither should be promoted.
ASSERT_EQ(&GetDocument(),
GetDocument().GetRootScrollerController().EffectiveRootScroller());
// Now make the second one invalid, that should cause the first to be
// promoted.
Element* container2 = GetDocument().getElementById("container2");
container2->style()->setProperty(&GetDocument(), "height", "95%", String(),
ASSERT_NO_EXCEPTION);
Compositor().BeginFrame();
Element* container = GetDocument().getElementById("container");
ASSERT_EQ(container,
GetDocument().GetRootScrollerController().EffectiveRootScroller());
}
// Test that when a valid iframe becomes loaded and thus should be promoted, it // Test that when a valid iframe becomes loaded and thus should be promoted, it
// becomes the root scroller, without needing an intervening layout. // becomes the root scroller, without needing an intervening layout.
TEST_F(ImplicitRootScrollerSimTest, IframeLoadedWithoutLayout) { TEST_F(ImplicitRootScrollerSimTest, IframeLoadedWithoutLayout) {
......
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