auto merge of #5062 : Adenilson/servo/printDisplayList01, r=pcwalton

This patch will iterate through the DisplayList after the reflow is done and print its elements (as also any sub-lists associated to a child node stacking context).

components/gfx/display_list/mod.rs

@@ -148,6 +148,53 @@ impl DisplayList {
         }
         result
     }
+
+    // Print the display list. Only makes sense to call it after performing reflow.
+    pub fn print_items(&self, mut indentation: String) {
+        let min_length = 4;
+        // We cover the case of an empty string.
+        if indentation.len() == 0 {
+            indentation = String::from_str("####");
+        }
+
+        // We grow the indentation by 4 characters if needed.
+        // I wish to push it all as a slice, but it won't work if the string is a single char.
+        while indentation.len() < min_length {
+            let c = indentation.char_at(0);
+            indentation.push(c);
+        }
+
+        // Closures are so nice!
+        let doit = |items: &Vec<DisplayItem>| {
+            for item in items.iter() {
+                match *item {
+                    // TODO(savago): would be nice to have other information associated with
+                    // each display item (e.g. coordinates?).
+                    DisplayItem::SolidColorClass(ref solid_color) => println!("{} SolidColor.", indentation),
+                    DisplayItem::TextClass(ref text) => println!("{} TextClass.", indentation),
+                    DisplayItem::ImageClass(ref image_item) => println!("{} ImageClass.", indentation),
+                    DisplayItem::BorderClass(ref image_item) => println!("{} BorderClass.", indentation),
+                    DisplayItem::GradientClass(ref image_item) => println!("{} GradientClass.", indentation),
+                    DisplayItem::LineClass(ref line_item) => println!("{} LineClass.", indentation),
+                    DisplayItem::BoxShadowClass(ref box_shadow_item) => println!("{} BoxShadowClass.", indentation),
+                }
+            }
+            println!("\n");
+        };
+
+        doit(&(self.all_display_items()));
+        if self.children.len() != 0 {
+            println!("{} Children stacking contexts list length: {}", indentation, self.children.len());
+            for subitem in self.children.iter() {
+                doit(&subitem.display_list.all_display_items());
+                if subitem.display_list.children.len() != 0 {
+                    // Rant: String doesn't have a substr() method that won't overflow if the
+                    // selected range is bigger than the string length.
+                    subitem.display_list.print_items(indentation.clone()+indentation.slice(0, min_length));
+                }
+            }
+        }
+    }
 }
 
 /// Represents one CSS stacking context, which may or may not have a hardware layer.

components/layout/layout_task.rs

@@ -709,6 +709,12 @@ impl LayoutTask {
                                                        color,
                                                        ScrollPolicy::Scrollable));
             let origin = Rect(Point2D(Au(0), Au(0)), root_size);
+
+            if opts::get().dump_display_list {
+                println!("#### start printing display list.");
+                display_list.print_items(String::from_str("#"));
+            }
+
             let stacking_context = Arc::new(StackingContext::new(display_list,
                                                                  &origin,
                                                                  &origin,

components/util/opts.rs

@@ -110,6 +110,9 @@ pub struct Opts {
     /// Dumps the flow tree after a layout.
     pub dump_flow_tree: bool,
 
+    /// Dumps the flow tree after a layout.
+    pub dump_display_list: bool,
+
     /// Whether to show an error when display list geometry escapes flow overflow regions.
     pub validate_display_list_geometry: bool,
 
@@ -132,6 +135,7 @@ pub fn print_debug_usage(app: &str)  {
     print_option("bubble-widths", "Bubble intrinsic widths separately like other engines.");
     print_option("disable-text-aa", "Disable antialiasing of rendered text.");
     print_option("dump-flow-tree", "Print the flow tree after each layout.");
+    print_option("dump-display-list", "Print the display list after each layout.");
     print_option("profile-tasks", "Instrument each task, writing the output to a file.");
     print_option("show-compositor-borders", "Paint borders along layer and tile boundaries.");
     print_option("show-fragment-borders", "Paint borders along fragment boundaries.");
@@ -183,6 +187,7 @@ pub fn default_opts() -> Opts {
         initial_window_size: TypedSize2D(800, 600),
         user_agent: None,
         dump_flow_tree: false,
+        dump_display_list: false,
         validate_display_list_geometry: false,
         profile_tasks: false,
         resources_path: None,
@@ -330,6 +335,7 @@ pub fn from_cmdline_args(args: &[String]) -> bool {
         show_debug_parallel_layout: debug_options.contains(&"show-parallel-layout"),
         enable_text_antialiasing: !debug_options.contains(&"disable-text-aa"),
         dump_flow_tree: debug_options.contains(&"dump-flow-tree"),
+        dump_display_list: debug_options.contains(&"dump-display-list"),
         validate_display_list_geometry: debug_options.contains(&"validate-display-list-geometry"),
         resources_path: opt_match.opt_str("resources-path"),
     };