From cd42c28f5b819357d037c67f33e993fbe9bbb75d Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Fri, 17 Oct 2014 22:35:56 -0700
Subject: [PATCH] gfx: Don't needlessly push and pop clip rects all the time.

15% painting improvement on CNN.
---
 components/gfx/display_list/mod.rs | 19 ++++++++++---------
 components/gfx/render_task.rs      |  8 +++-----
 2 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/components/gfx/display_list/mod.rs b/components/gfx/display_list/mod.rs
index a72f0b44d08..7f8975a2ca6 100644
--- a/components/gfx/display_list/mod.rs
+++ b/components/gfx/display_list/mod.rs
@@ -288,10 +288,10 @@ impl DisplayList {
     pub fn draw_into_context(&self,
                              render_context: &mut RenderContext,
                              current_transform: &Matrix2D<AzFloat>,
-                             current_clip_rect: &Rect<Au>) {
+                             current_clip_stack: &mut Vec<Rect<Au>>) {
         debug!("Beginning display list.");
         for item in self.list.iter() {
-            item.draw_into_context(render_context, current_transform, current_clip_rect)
+            item.draw_into_context(render_context, current_transform, current_clip_stack)
         }
         debug!("Ending display list.");
     }
@@ -504,14 +504,19 @@ impl DisplayItem {
     fn draw_into_context(&self,
                          render_context: &mut RenderContext,
                          current_transform: &Matrix2D<AzFloat>,
-                         current_clip_rect: &Rect<Au>) {
+                         current_clip_stack: &mut Vec<Rect<Au>>) {
         // This should have been flattened to the content stacking level first.
         assert!(self.base().level == ContentStackingLevel);
 
+        // TODO(pcwalton): This will need some tweaking to deal with more complex clipping regions.
         let clip_rect = &self.base().clip_rect;
-        let need_to_clip = current_clip_rect != clip_rect;
-        if need_to_clip {
+        if current_clip_stack.len() == 0 || current_clip_stack.last().unwrap() != clip_rect {
+            while current_clip_stack.len() != 0 {
+                render_context.draw_pop_clip();
+                drop(current_clip_stack.pop());
+            }
             render_context.draw_push_clip(clip_rect);
+            current_clip_stack.push(*clip_rect);
         }
 
         match *self {
@@ -608,10 +613,6 @@ impl DisplayItem {
 
             PseudoDisplayItemClass(_) => {}
         }
-
-        if need_to_clip {
-            render_context.draw_pop_clip();
-        }
     }
 
     pub fn base<'a>(&'a self) -> &'a BaseDisplayItem {
diff --git a/components/gfx/render_task.rs b/components/gfx/render_task.rs
index 53f50f95102..32c5d97c2b1 100644
--- a/components/gfx/render_task.rs
+++ b/components/gfx/render_task.rs
@@ -25,14 +25,13 @@ use servo_msg::compositor_msg::{LayerMetadata, RenderListener, RenderingRenderSt
 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::{Au, mod};
+use servo_util::geometry;
 use servo_util::opts;
 use servo_util::smallvec::{SmallVec, SmallVec1};
 use servo_util::task::spawn_named_with_send_on_failure;
 use servo_util::time::{TimeProfilerChan, profile};
 use servo_util::time;
 use std::comm::{Receiver, Sender, channel};
-use std::i32;
 use sync::Arc;
 use font_cache_task::FontCacheTask;
 
@@ -359,9 +358,8 @@ impl<C:RenderListener + Send> RenderTask<C> {
                             None,
                             self.time_profiler_chan.clone(),
                             || {
-                        let clip_rect = Rect(Point2D(Au(i32::MIN), Au(i32::MIN)),
-                                             Size2D(Au(i32::MAX), Au(i32::MAX)));
-                        display_list.draw_into_context(&mut ctx, &matrix, &clip_rect);
+                        let mut clip_stack = Vec::new();
+                        display_list.draw_into_context(&mut ctx, &matrix, &mut clip_stack);
                         ctx.draw_target.flush();
                     });
                 }