LibWeb: Account for negative margins when calculating float intrusion

awesomekling · awesomekling · commit 89ba00304ce8 · 2023-06-04T18:14:12.000+02:00
If a box has a negative margin-left, it may have a negative effective
offset within its parent BFC root coordinate system.

We can account for this when calculating the amount of left-side float
intrusion by flooring the X offset at 0.
diff --git a/Tests/LibWeb/Layout/expected/block-and-inline/block-with-negative-margin-and-no-intruding-floats.txt b/Tests/LibWeb/Layout/expected/block-and-inline/block-with-negative-margin-and-no-intruding-floats.txt
@@ -0,0 +1,11 @@
+Viewport <#document> at (0,0) content-size 800x600 children: not-inline
+  BlockContainer <html> at (1,1) content-size 798x55.40625 [BFC] children: not-inline
+    BlockContainer <body> at (110,10) content-size 300x37.40625 positioned children: not-inline
+      BlockContainer <div> at (61,11) content-size 200x35.40625 children: inline
+        line 0 width: 159.859375, height: 17.46875, bottom: 17.46875, baseline: 13.53125
+          frag 0 from TextNode start: 0, length: 19, rect: [61,11 159.859375x17.46875]
+            "there are no floats"
+        line 1 width: 163.875, height: 17.9375, bottom: 35.40625, baseline: 13.53125
+          frag 0 from TextNode start: 20, length: 21, rect: [61,28 163.875x17.46875]
+            "intruding on this div"
+        TextNode <#text>
diff --git a/Tests/LibWeb/Layout/input/block-and-inline/block-with-negative-margin-and-no-intruding-floats.html b/Tests/LibWeb/Layout/input/block-and-inline/block-with-negative-margin-and-no-intruding-floats.html
@@ -0,0 +1,15 @@
+<!doctype html><style>
+* { border: 1px solid black; }
+html { background: white; }
+body { 
+    position: relative;
+    left: 100px;
+    background: pink;
+    width: 300px;
+}
+div {
+    margin-left: -50px;
+    background: orange;
+    width: 200px;
+}
+</style><body><div>there are no floats intruding on this div
diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
@@ -1066,7 +1066,7 @@ FormattingContext::SpaceUsedByFloats BlockFormattingContext::intrusion_by_floats
     CSSPixels y_in_root = box_in_root_rect.y() + y_in_box;
     auto space_used_by_floats_in_root = space_used_by_floats(y_in_root);
 
-    auto left_intrusion = max(CSSPixels(0), space_used_by_floats_in_root.left - box_in_root_rect.x());
+    auto left_intrusion = max(CSSPixels(0), space_used_by_floats_in_root.left - max(CSSPixels(0), box_in_root_rect.x()));
 
     CSSPixels offset_from_containing_block_chain_margins_between_here_and_root = 0;
     for (auto const* containing_block = static_cast<Box const*>(&box); containing_block && containing_block != &root(); containing_block = containing_block->containing_block()) {
diff --git a/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp
@@ -51,7 +51,7 @@ CSSPixels InlineFormattingContext::leftmost_x_offset_at(CSSPixels y) const
     }
     // The left edge of the containing block is to the left of the rightmost left-side float.
     // We adjust the inline content insertion point by the overlap between the containing block and the float.
-    return space.left - box_in_root_rect.x();
+    return space.left - max(CSSPixels(0), box_in_root_rect.x());
 }
 
 CSSPixels InlineFormattingContext::available_space_for_line(CSSPixels y) const

Original file line number	Diff line number	Diff line change
`@@ -51,7 +51,7 @@ CSSPixels InlineFormattingContext::leftmost_x_offset_at(CSSPixels y) const`
`51`	`51`	`}`
`52`	`52`	`// The left edge of the containing block is to the left of the rightmost left-side float.`
`53`	`53`	`// We adjust the inline content insertion point by the overlap between the containing block and the float.`
`54`		`- return space.left - box_in_root_rect.x();`
	`54`	`+ return space.left - max(CSSPixels(0), box_in_root_rect.x());`
`55`	`55`	`}`
`56`	`56`
`57`	`57`	`CSSPixels InlineFormattingContext::available_space_for_line(CSSPixels y) const`