Cache font-style and text-decoration to speed up can_merge_with_box()

src/components/main/layout/box.rs

@@ -114,6 +114,11 @@ impl TextRenderBox {
 pub struct UnscannedTextRenderBox {
     base: RenderBoxBase,
     text: ~str,
+
+    // Cache font-style and text-decoration to check whether
+    // this box can merge with another render box.
+    font_style: Option<FontStyle>,
+    text_decoration: Option<CSSTextDecoration>,
 }
 
 impl UnscannedTextRenderBox {
@@ -128,6 +133,8 @@ impl UnscannedTextRenderBox {
             UnscannedTextRenderBox {
                 base: base,
                 text: text_node.element.data.to_str(),
+                font_style: None,
+                text_decoration: None,
             }
         }
     }
@@ -824,9 +831,10 @@ impl RenderBox {
 
     /// Converts this node's computed style to a font style used for rendering.
     pub fn font_style(&self) -> FontStyle {
-        let my_style = self.nearest_ancestor_element().style();
+        fn get_font_style(element: AbstractNode<LayoutView>) -> FontStyle {
+            let my_style = element.style();
 
-        debug!("(font style) start: %?", self.nearest_ancestor_element().type_id());
+            debug!("(font style) start: %?", element.type_id());
 
             // FIXME: Too much allocation here.
             let font_families = do my_style.font_family().map |family| {
@@ -865,6 +873,30 @@ impl RenderBox {
             }
         }
 
+        let font_style_cached = match *self {
+            UnscannedTextRenderBoxClass(ref box) => {
+                match box.font_style {
+                    Some(ref style) => Some(style.clone()),
+                    None => None
+                }
+            }
+            _ => None
+        };
+
+        if font_style_cached.is_some() {
+            return font_style_cached.unwrap();
+        } else {
+            let font_style = get_font_style(self.nearest_ancestor_element());
+            match *self {
+                UnscannedTextRenderBoxClass(ref box) => {
+                    box.font_style = Some(font_style.clone());
+                }
+                _ => ()
+            }
+            return font_style;
+        }
+    }
+
     /// Returns the text alignment of the computed style of the nearest ancestor-or-self `Element`
     /// node.
     pub fn text_align(&self) -> CSSTextAlign {
@@ -916,7 +948,29 @@ impl RenderBox {
                 text_decoration
             }
         }
-        get_propagated_text_decoration(self.nearest_ancestor_element())
+
+        let text_decoration_cached = match *self {
+            UnscannedTextRenderBoxClass(ref box) => {
+                match box.text_decoration {
+                    Some(ref decoration) => Some(decoration.clone()),
+                    None => None
+                }
+            }
+            _ => None
+        };
+
+        if text_decoration_cached.is_some() {
+            return text_decoration_cached.unwrap();
+        } else {
+            let text_decoration = get_propagated_text_decoration(self.nearest_ancestor_element());
+            match *self {
+                UnscannedTextRenderBoxClass(ref box) => {
+                    box.text_decoration = Some(text_decoration.clone());
+                }
+                _ => ()
+            }
+            return text_decoration;
+        }
     }
 
     /// Dumps this node, for debugging.