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Refactor NGLayoutOpportunityIterator to use 3-nodes spatial tree
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This patch introduces a new layout opportunity iterator algorithm which is based on 3-nodes spatial tree. The new approach has several benefits from the existing one:
- improved runtime complexity to find layout opportunities: O(N log N)
- ability to reuse the tree, e.g. just insert a new exclusion down into the tree. Insert operation shouldn't take longer than 2 x log N time.

BUG=635619

Review-Url: https://codereview.chromium.org/2410773006
Cr-Commit-Position: refs/heads/master@{#425391}
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glebl authored and Commit bot committed Oct 14, 2016
1 parent ddef07a commit e871b54
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Showing 9 changed files with 347 additions and 251 deletions.
1 change: 1 addition & 0 deletions third_party/WebKit/Source/core/layout/BUILD.gn
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Original file line number Diff line number Diff line change
Expand Up @@ -296,6 +296,7 @@ blink_core_sources("layout") {
"ng/ng_layout_input_text.h",
"ng/ng_layout_opportunity_iterator.cc",
"ng/ng_layout_opportunity_iterator.h",
"ng/ng_layout_opportunity_tree_node.h",
"ng/ng_length_utils.cc",
"ng/ng_length_utils.h",
"ng/ng_physical_constraint_space.cc",
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2 changes: 1 addition & 1 deletion third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
is_new_fc_(false) {
physical_space_ =
new NGPhysicalConstraintSpace(size.ConvertToPhysical(writing_mode));
for (const NGExclusion& exclusion : other.PhysicalSpace()->Exclusions()) {
for (const auto& exclusion : other.PhysicalSpace()->Exclusions()) {
physical_space_->AddExclusion(exclusion);
}
}
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99 changes: 63 additions & 36 deletions third_party/WebKit/Source/core/layout/ng/ng_constraint_space_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -70,8 +70,8 @@ TEST(NGConstraintSpaceTest, LayoutOpportunitiesTopRightExclusion) {
auto* physical_space = new NGPhysicalConstraintSpace(physical_size);

// Add a 100x100 exclusion in the top right corner.
physical_space->AddExclusion(NGExclusion(LayoutUnit(0), LayoutUnit(600),
LayoutUnit(100), LayoutUnit(500)));
physical_space->AddExclusion(new NGExclusion(
LayoutUnit(0), LayoutUnit(600), LayoutUnit(100), LayoutUnit(500)));

auto* space =
new NGConstraintSpace(HorizontalTopBottom, LeftToRight, physical_space);
Expand All @@ -95,8 +95,8 @@ TEST(NGConstraintSpaceTest, LayoutOpportunitiesTopLeftExclusion) {
auto* physical_space = new NGPhysicalConstraintSpace(physical_size);

// Add a 100x100 exclusion in the top left corner.
physical_space->AddExclusion(NGExclusion(LayoutUnit(0), LayoutUnit(100),
LayoutUnit(100), LayoutUnit(0)));
physical_space->AddExclusion(new NGExclusion(LayoutUnit(0), LayoutUnit(100),
LayoutUnit(100), LayoutUnit(0)));

auto* space =
new NGConstraintSpace(HorizontalTopBottom, LeftToRight, physical_space);
Expand All @@ -113,70 +113,97 @@ TEST(NGConstraintSpaceTest, LayoutOpportunitiesTopLeftExclusion) {
EXPECT_EQ("(null)", OpportunityToString(iterator->Next()));
}

// Verifies that Layout Opportunity iterator produces 7 layout opportunities
// from 4 start points created by 2 CSS exclusions positioned in the middle of
// the main constraint space.
//
// Test case visual representation:
//
// 100 200 300 400 500
// +----|----|----|----|----|----+
// (1)--|----|----|-(2)|----|-(3)+
// 50 | |
// 100 | |
// 150 | |
// 200 | ********** |
// 250 | ********** |
// 300 | |
// 300 (4) |
// 350 | *** |
// +-----------------------------+
//
// Expected:
// Layout opportunity iterator generates the next opportunities:
// - 1st Start Point: 0,0 600x200; 0,0 150x400
// - 2nd Start Point: 250,0 350x350; 250,0 250x400
// - 3rd Start Point: 550,0 50x400
// - 4th Start Point: 0,300 600x50; 0,300 500x100
TEST(NGConstraintSpaceTest, LayoutOpportunitiesTwoInMiddle) {
NGPhysicalSize physical_size;
physical_size.width = LayoutUnit(600);
physical_size.height = LayoutUnit(400);
auto* physical_space = new NGPhysicalConstraintSpace(physical_size);

// Add a 200x100 exclusion at 150x200
physical_space->AddExclusion(NGExclusion(LayoutUnit(200), LayoutUnit(250),
LayoutUnit(300), LayoutUnit(150)));
// Add a 50x50 exclusion at 500x350
physical_space->AddExclusion(NGExclusion(LayoutUnit(350), LayoutUnit(550),
LayoutUnit(400), LayoutUnit(500)));
// Add exclusions
physical_space->AddExclusion(new NGExclusion(
LayoutUnit(200), LayoutUnit(250), LayoutUnit(300), LayoutUnit(150)));
physical_space->AddExclusion(new NGExclusion(
LayoutUnit(350), LayoutUnit(550), LayoutUnit(400), LayoutUnit(500)));

auto* space =
new NGConstraintSpace(HorizontalTopBottom, LeftToRight, physical_space);
bool for_inline_or_bfc = true;
auto* iterator = space->LayoutOpportunities(NGClearNone, for_inline_or_bfc);

// First opportunity should be above the first exclusion.
// 1st Start point
EXPECT_EQ("0,0 600x200", OpportunityToString(iterator->Next()));

// Second opportunity should be full height to the left.
EXPECT_EQ("0,0 150x400", OpportunityToString(iterator->Next()));

// Third opportunity should be to the left of the first exclusion. This is a
// subset of the second opportunity but has a different location and might
// have a different alignment.
EXPECT_EQ("0,200 150x200", OpportunityToString(iterator->Next()));

// Fourth opportunity should be to the right of the first exclusion extending
// down until the top of the second exclusion.
EXPECT_EQ("250,200 350x150", OpportunityToString(iterator->Next()));
// 2nd Start point
EXPECT_EQ("250,0 350x350", OpportunityToString(iterator->Next()));
EXPECT_EQ("250,0 250x400", OpportunityToString(iterator->Next()));

// Fifth opportunity should be to the right of the first exclusion until the
// left edge of the second exclusion and extending all the way down.
EXPECT_EQ("250,200 250x200", OpportunityToString(iterator->Next()));
// 3rd Start point
EXPECT_EQ("550,0 50x400", OpportunityToString(iterator->Next()));

// Sixth opportunity should be below first exclusion with full width.
// 4th Start point
EXPECT_EQ("0,300 600x50", OpportunityToString(iterator->Next()));

// Seventh opportunity should be below first exclusion until the left edge of
// the second exclusion extending all the way down.
EXPECT_EQ("0,300 500x100", OpportunityToString(iterator->Next()));

// Eight exclusion should be to the left of the last exclusion.
EXPECT_EQ("0,350 500x50", OpportunityToString(iterator->Next()));
// Iterator is exhausted.
EXPECT_EQ("(null)", OpportunityToString(iterator->Next()));
}

// Ninth exclusion should be to the right of the last exclusion.
EXPECT_EQ("550,350 50x50", OpportunityToString(iterator->Next()));
// Verifies that Layout Opportunity iterator ignores the exclusion that is not
// within constraint space.
//
// Test case visual representation:
//
// 100 200 300 400 500
// +----|----|----|----|----|----+
// 50 | |
// 100 | |
// +-----------------------------+
// *** <- Exclusion
//
// Expected:
// Layout opportunity iterator generates only one opportunity that equals to
// available constraint space, i.e. 0,0 600x200
TEST(NGConstraintSpaceTest, LayoutOpportunitiesWithOutOfBoundsExclusions) {
NGPhysicalSize physical_size;
physical_size.width = LayoutUnit(600);
physical_size.height = LayoutUnit(100);

auto* physical_space = new NGPhysicalConstraintSpace(physical_size);
physical_space->AddExclusion(new NGExclusion(LayoutUnit(150), LayoutUnit(100),
LayoutUnit(200), LayoutUnit(0)));
auto* space =
new NGConstraintSpace(HorizontalTopBottom, LeftToRight, physical_space);

// There should be no tenth opportunity.
bool for_inline_or_bfc = true;
auto* iterator = space->LayoutOpportunities(NGClearNone, for_inline_or_bfc);

EXPECT_EQ("0,0 600x100", OpportunityToString(iterator->Next()));
EXPECT_EQ("(null)", OpportunityToString(iterator->Next()));
}

} // namespace

} // namespace blink
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