LibWeb: Break lines until we have enough space between floats

Before this change, we'd always insert one line box fragment, even when
a float was taking up too much space on the line, and the fragment
didn't actually fit.

We now perform line breaks until we have enough space between floats.
This fixes many page layouts where we'd previously see small fragments
of inline content outside the right edge of the containing block.

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp

@@ -297,4 +297,12 @@ void InlineFormattingContext::generate_line_boxes(LayoutMode layout_mode)
     }
 }
 
+bool InlineFormattingContext::any_floats_intrude_at_y(float y) const
+{
+    auto box_in_root_rect = content_box_rect_in_ancestor_coordinate_space(containing_block(), parent().root(), m_state);
+    float y_in_root = box_in_root_rect.y() + y;
+    auto space = parent().space_used_by_floats(y_in_root);
+    return space.left > 0 || space.right > 0;
+}
+
 }

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.h

@@ -29,6 +29,7 @@ public:
 
     float leftmost_x_offset_at(float y) const;
     float available_space_for_line(float y) const;
+    bool any_floats_intrude_at_y(float y) const;
 
     float effective_containing_block_width() const { return m_effective_containing_block_width; }
 

Userland/Libraries/LibWeb/Layout/LineBuilder.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibWeb/Layout/BlockFormattingContext.h>
 #include <LibWeb/Layout/LineBuilder.h>
 #include <LibWeb/Layout/TextNode.h>
 
@@ -23,11 +24,15 @@ LineBuilder::~LineBuilder()
         update_last_line();
 }
 
-void LineBuilder::break_line()
+void LineBuilder::break_line(Optional<float> next_item_width)
 {
     update_last_line();
-    m_containing_block_state.line_boxes.append(LineBox());
-    begin_new_line(true);
+    do {
+        m_containing_block_state.line_boxes.append(LineBox());
+        begin_new_line(true);
+    } while (next_item_width.has_value()
+        && next_item_width.value() > m_available_width_for_current_line
+        && m_context.any_floats_intrude_at_y(m_current_y));
 }
 
 void LineBuilder::begin_new_line(bool increment_y)
@@ -68,11 +73,18 @@ void LineBuilder::append_text_chunk(TextNode const& text_node, size_t offset_in_
 
 bool LineBuilder::should_break(float next_item_width)
 {
-    auto const& line_boxes = m_containing_block_state.line_boxes;
-    if (line_boxes.is_empty() || line_boxes.last().is_empty())
+    if (!isfinite(m_available_width_for_current_line))
         return false;
-    auto current_line_width = line_boxes.last().width();
-    return (current_line_width + next_item_width) > m_available_width_for_current_line;
+
+    auto const& line_boxes = m_containing_block_state.line_boxes;
+    if (line_boxes.is_empty() || line_boxes.last().is_empty()) {
+        // If we don't have a single line box yet *and* there are no floats intruding
+        // at this Y coordinate, we don't need to break before inserting anything.
+        if (!m_context.any_floats_intrude_at_y(m_current_y))
+            return false;
+    }
+    auto current_line_width = ensure_last_line_box().width();
+    return roundf(current_line_width + next_item_width) > m_available_width_for_current_line;
 }
 
 static float box_baseline(LayoutState const& state, Box const& box)
@@ -255,7 +267,6 @@ void LineBuilder::adjust_last_line_after_inserting_floating_box(Badge<BlockForma
     if (float_ == CSS::Float::Left && !m_containing_block_state.line_boxes.is_empty()) {
         for (auto& fragment : m_containing_block_state.line_boxes.last().fragments())
             fragment.set_offset(fragment.offset().translated(space_used_by_float, 0));
-        m_containing_block_state.line_boxes.last().m_width += space_used_by_float;
     }
 
     m_available_width_for_current_line -= space_used_by_float;

Userland/Libraries/LibWeb/Layout/LineBuilder.h

@@ -18,7 +18,7 @@ public:
     LineBuilder(InlineFormattingContext&, LayoutState&);
     ~LineBuilder();
 
-    void break_line();
+    void break_line(Optional<float> next_item_width = {});
     void append_box(Box const&, float leading_size, float trailing_size, float leading_margin, float trailing_margin);
     void append_text_chunk(TextNode const&, size_t offset_in_node, size_t length_in_node, float leading_size, float trailing_size, float leading_margin, float trailing_margin, float content_width, float content_height);
 
@@ -26,7 +26,7 @@ public:
     bool break_if_needed(float next_item_width)
     {
         if (should_break(next_item_width)) {
-            break_line();
+            break_line(next_item_width);
             return true;
         }
         return false;