Auto merge of #7292 - pcwalton:layer-sorting, r=glennw

gfx: Sort layers according to their Z-index value before handing them off to the compositor.

Closes #7166.

r? @glennw

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1 files changed, 8 insertions, 0 deletions

diff --git a/components/gfx/paint_task.rs b/components/gfx/paint_task.rs
index 175a7b040f1..26c5308ae3e 100644
--- a/components/gfx/paint_task.rs
+++ b/components/gfx/paint_task.rs
@@ -27,6 +27,7 @@ use msg::constellation_msg::PipelineExitType;
 use profile_traits::mem::{self, ReportsChan};
 use profile_traits::time::{self, profile};
 use rand::{self, Rng};
+use smallvec::SmallVec;
 use skia::gl_context::GLContext;
 use std::borrow::ToOwned;
 use std::mem as std_mem;
@@ -393,7 +394,14 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
                 }
             };
 
+            // Sort positioned children according to z-index.
+            let mut positioned_children: SmallVec<[Arc<StackingContext>; 8]> = SmallVec::new();
             for kid in &stacking_context.display_list.children {
+                positioned_children.push((*kid).clone());
+            }
+            positioned_children.sort_by(|this, other| this.z_index.cmp(&other.z_index));
+
+            for kid in positioned_children.iter() {
                 build(properties, &**kid, &page_position, &transform, &perspective, next_parent_id)
             }
         }