LibWeb: Layout grid items after calculation

Now that the positions of each grid item have been calculated, and the
sizes of the individual rows and columns ascertained, can actually
layout the different items.

Author: martinfalisse

Userland/Libraries/LibWeb/Layout/GridFormattingContext.cpp

@@ -369,6 +369,10 @@ void GridFormattingContext::run(Box const& box, LayoutMode)
         // FIXME: 4.2. For dense packing:
     }
 
+    for (auto& positioned_box : positioned_boxes) {
+        (void)layout_inside(positioned_box.box, LayoutMode::Normal);
+    }
+
     // https://drafts.csswg.org/css-grid/#overview-sizing
     // 2.3. Sizing the Grid
     // Once the grid items have been placed, the sizes of the grid tracks (rows and columns) are
@@ -965,6 +969,29 @@ void GridFormattingContext::run(Box const& box, LayoutMode)
         if (grid_row.max_track_sizing_function.is_length() && grid_row.max_track_sizing_function.length().is_auto())
             grid_row.base_size = max(grid_row.base_size, remaining_vertical_space / count_of_auto_max_row_tracks);
     }
+
+    // Do layout
+    auto layout_box = [&](int row_start, int row_end, int column_start, int column_end, Box const& child_box) -> void {
+        auto& child_box_state = m_state.get_mutable(child_box);
+        float x_start = 0;
+        float x_end = 0;
+        float y_start = 0;
+        float y_end = 0;
+        for (int i = 0; i < column_start; i++)
+            x_start += grid_columns[i].base_size;
+        for (int i = 0; i < column_end; i++)
+            x_end += grid_columns[i].base_size;
+        for (int i = 0; i < row_start; i++)
+            y_start += grid_rows[i].base_size;
+        for (int i = 0; i < row_end; i++)
+            y_end += grid_rows[i].base_size;
+        child_box_state.set_content_width(x_end - x_start);
+        child_box_state.set_content_height(y_end - y_start);
+        child_box_state.offset = { x_start, y_start };
+    };
+
+    for (auto& positioned_box : positioned_boxes)
+        layout_box(positioned_box.row, positioned_box.row + positioned_box.row_span, positioned_box.column, positioned_box.column + positioned_box.column_span, positioned_box.box);
 }
 
 }