gfx: Add display list optimization to eliminate clipped items before

submitting them to Skia.

40x improvement in painting time on Wikipedia.

src/components/gfx/display_list/mod.rs

@@ -33,6 +33,8 @@ use std::slice::Items;
 use style::computed_values::border_style;
 use sync::Arc;
 
+pub mod optimizer;
+
 /// An opaque handle to a node. The only safe operation that can be performed on this node is to
 /// compare it to another opaque handle or to another node.
 ///
@@ -51,7 +53,7 @@ impl OpaqueNode {
 }
 
 /// "Steps" as defined by CSS 2.1 § E.2.
-#[deriving(Eq)]
+#[deriving(Clone, Eq)]
 pub enum StackingLevel {
     /// The border and backgrounds for the root of this stacking context: steps 1 and 2.
     BackgroundAndBordersStackingLevel,
@@ -207,6 +209,7 @@ pub enum BackgroundAndBorderLevel {
 }
 
 /// A list of rendering operations to be performed.
+#[deriving(Clone)]
 pub struct DisplayList {
     pub list: DList<DisplayItem>,
 }
@@ -331,6 +334,7 @@ impl DisplayList {
 }
 
 /// One drawing command in the list.
+#[deriving(Clone)]
 pub enum DisplayItem {
     SolidColorDisplayItemClass(Box<SolidColorDisplayItem>),
     TextDisplayItemClass(Box<TextDisplayItem>),
@@ -348,6 +352,7 @@ pub enum DisplayItem {
 }
 
 /// Information common to all display items.
+#[deriving(Clone)]
 pub struct BaseDisplayItem {
     /// The boundaries of the display item.
     ///
@@ -372,12 +377,14 @@ impl BaseDisplayItem {
 }
 
 /// Renders a solid color.
+#[deriving(Clone)]
 pub struct SolidColorDisplayItem {
     pub base: BaseDisplayItem,
     pub color: Color,
 }
 
 /// Text decoration information.
+#[deriving(Clone)]
 pub struct TextDecorations {
     /// The color to use for underlining, if any.
     pub underline: Option<Color>,
@@ -388,6 +395,7 @@ pub struct TextDecorations {
 }
 
 /// Renders text.
+#[deriving(Clone)]
 pub struct TextDisplayItem {
     /// Fields common to all display items.
     pub base: BaseDisplayItem,
@@ -406,6 +414,7 @@ pub struct TextDisplayItem {
 }
 
 /// Renders an image.
+#[deriving(Clone)]
 pub struct ImageDisplayItem {
     pub base: BaseDisplayItem,
     pub image: Arc<Box<Image>>,
@@ -417,6 +426,7 @@ pub struct ImageDisplayItem {
 }
 
 /// Renders a border.
+#[deriving(Clone)]
 pub struct BorderDisplayItem {
     pub base: BaseDisplayItem,
 
@@ -431,6 +441,7 @@ pub struct BorderDisplayItem {
 }
 
 /// Renders a line segment.
+#[deriving(Clone)]
 pub struct LineDisplayItem {
     pub base: BaseDisplayItem,
 
@@ -442,6 +453,7 @@ pub struct LineDisplayItem {
 }
 
 /// Clips a list of child display items to this display item's boundaries.
+#[deriving(Clone)]
 pub struct ClipDisplayItem {
     /// The base information.
     pub base: BaseDisplayItem,

src/components/gfx/display_list/optimizer.rs

@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use display_list::{BorderDisplayItemClass, ClipDisplayItem, ClipDisplayItemClass, DisplayItem};
+use display_list::{DisplayList, ImageDisplayItemClass, LineDisplayItemClass};
+use display_list::{PseudoDisplayItemClass, SolidColorDisplayItemClass, TextDisplayItemClass};
+
+use collections::deque::Deque;
+use collections::dlist::DList;
+use geom::rect::Rect;
+use servo_util::geometry::Au;
+use sync::Arc;
+
+pub struct DisplayListOptimizer {
+    display_list: Arc<DisplayList>,
+    /// The visible rect in page coordinates.
+    visible_rect: Rect<Au>,
+}
+
+impl DisplayListOptimizer {
+    /// `visible_rect` specifies the visible rect in page coordinates.
+    pub fn new(display_list: Arc<DisplayList>, visible_rect: Rect<Au>) -> DisplayListOptimizer {
+        DisplayListOptimizer {
+            display_list: display_list,
+            visible_rect: visible_rect,
+        }
+    }
+
+    pub fn optimize(self) -> DisplayList {
+        self.process_display_list(&*self.display_list)
+    }
+
+    fn process_display_list(&self, display_list: &DisplayList) -> DisplayList {
+        let mut result = DList::new();
+        for item in display_list.iter() {
+            match self.process_display_item(item) {
+                None => {}
+                Some(display_item) => result.push_back(display_item),
+            }
+        }
+        DisplayList {
+            list: result,
+        }
+    }
+
+    fn process_display_item(&self, display_item: &DisplayItem) -> Option<DisplayItem> {
+        // Eliminate display items outside the visible region.
+        if !self.visible_rect.intersects(&display_item.base().bounds) {
+            return None
+        }
+
+        // Recur.
+        match *display_item {
+            ClipDisplayItemClass(ref clip) => {
+                let new_children = self.process_display_list(&clip.children);
+                if new_children.is_empty() {
+                    return None
+                }
+                Some(ClipDisplayItemClass(box ClipDisplayItem {
+                    base: clip.base.clone(),
+                    children: new_children,
+                }))
+            }
+
+            BorderDisplayItemClass(_) | ImageDisplayItemClass(_) | LineDisplayItemClass(_) |
+            PseudoDisplayItemClass(_) | SolidColorDisplayItemClass(_) |
+            TextDisplayItemClass(_) => {
+                Some((*display_item).clone())
+            }
+        }
+    }
+}
+

src/components/gfx/gfx.rs

@@ -56,6 +56,7 @@ mod render_context;
 
 // Rendering
 pub mod color;
+#[path="display_list/mod.rs"]
 pub mod display_list;
 pub mod render_task;
 

src/components/gfx/render_task.rs

@@ -5,6 +5,7 @@
 //! The task that handles all rendering/painting.
 
 use buffer_map::BufferMap;
+use display_list::optimizer::DisplayListOptimizer;
 use display_list::DisplayList;
 use font_context::{FontContext, FontContextInfo};
 use render_context::RenderContext;
@@ -17,19 +18,18 @@ use geom::size::Size2D;
 use layers::platform::surface::{NativePaintingGraphicsContext, NativeSurface};
 use layers::platform::surface::{NativeSurfaceMethods};
 use layers;
-use servo_msg::compositor_msg::{Epoch, IdleRenderState, LayerBuffer};
-use servo_msg::compositor_msg::{LayerBufferSet, LayerId, LayerMetadata, RenderListener};
-use servo_msg::compositor_msg::{RenderingRenderState, ScrollPolicy};
-use servo_msg::constellation_msg::{ConstellationChan, PipelineId, RendererReadyMsg};
-use servo_msg::constellation_msg::{Failure, FailureMsg};
+use servo_msg::compositor_msg::{Epoch, IdleRenderState, LayerBuffer, LayerBufferSet, LayerId};
+use servo_msg::compositor_msg::{LayerMetadata, RenderListener, RenderingRenderState, ScrollPolicy};
+use servo_msg::constellation_msg::{ConstellationChan, Failure, FailureMsg, PipelineId};
+use servo_msg::constellation_msg::{RendererReadyMsg};
 use servo_msg::platform::surface::NativeSurfaceAzureMethods;
+use servo_util::geometry;
 use servo_util::opts::Opts;
 use servo_util::smallvec::{SmallVec, SmallVec1};
+use servo_util::task::send_on_failure;
 use servo_util::time::{ProfilerChan, profile};
 use servo_util::time;
-use servo_util::task::send_on_failure;
-
-use std::comm::{channel, Receiver, Sender};
+use std::comm::{Receiver, Sender, channel};
 use std::task::TaskBuilder;
 use sync::Arc;
 
@@ -294,6 +294,12 @@ impl<C: RenderListener + Send> RenderTask<C> {
 
             // Divide up the layer into tiles.
             for tile in tiles.iter() {
+                // Optimize the display list for this tile.
+                let page_rect_au = geometry::f32_rect_to_au_rect(tile.page_rect);
+                let optimizer = DisplayListOptimizer::new(render_layer.display_list.clone(),
+                                                          page_rect_au);
+                let display_list = optimizer.optimize();
+
                 let width = tile.screen_rect.size.width;
                 let height = tile.screen_rect.size.height;
 
@@ -340,7 +346,7 @@ impl<C: RenderListener + Send> RenderTask<C> {
 
                     // Draw the display list.
                     profile(time::RenderingDrawingCategory, self.profiler_chan.clone(), || {
-                        render_layer.display_list.draw_into_context(&mut ctx);
+                        display_list.draw_into_context(&mut ctx);
                         ctx.draw_target.flush();
                     });
                 }

src/components/util/geometry.rs

@@ -4,6 +4,7 @@
 
 use geom::point::Point2D;
 use geom::rect::Rect;
+use geom::size::Size2D;
 
 use std::default::Default;
 use std::num::{NumCast, One, Zero};
@@ -159,6 +160,11 @@ impl Au {
                        else { return Au(s - res) };
     }
 
+    #[inline]
+    pub fn from_frac32_px(px: f32) -> Au {
+        Au((px * 60f32) as i32)
+    }
+
     #[inline]
     pub fn from_pt(pt: f64) -> Au {
         from_px(pt_to_px(pt) as int)
@@ -231,3 +237,9 @@ pub fn rect_contains_point<T:Ord + Add<T,T>>(rect: Rect<T>, point: Point2D<T>) -
         point.y >= rect.origin.y && point.y < rect.origin.y + rect.size.height
 }
 
+/// A helper function to convert a rect of `f32` pixels to a rect of app units.
+pub fn f32_rect_to_au_rect(rect: Rect<f32>) -> Rect<Au> {
+    Rect(Point2D(Au::from_frac32_px(rect.origin.x), Au::from_frac32_px(rect.origin.y)),
+         Size2D(Au::from_frac32_px(rect.size.width), Au::from_frac32_px(rect.size.height)))
+}
+