3 files changed, 23 insertions, 4 deletions
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 10e13c90a5b..0d261092bb4 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -35,7 +35,7 @@ use dom::bindings::utils::{Reflectable, Reflector, WindowProxyHandler};
 use script_task::ScriptChan;
 
 use canvas::canvas_paint_task::{CanvasGradientStop, LinearGradientStyle, RadialGradientStyle};
-use canvas::canvas_paint_task::{LineCapStyle, LineJoinStyle};
+use canvas::canvas_paint_task::{LineCapStyle, LineJoinStyle, CompositionOrBlending};
 use cssparser::RGBA;
 use encoding::types::EncodingRef;
 use geom::matrix2d::Matrix2D;
@@ -270,7 +270,7 @@ no_jsmanaged_fields!(RGBA);
 no_jsmanaged_fields!(Matrix2D<T>);
 no_jsmanaged_fields!(StorageType);
 no_jsmanaged_fields!(CanvasGradientStop, LinearGradientStyle, RadialGradientStyle);
-no_jsmanaged_fields!(LineCapStyle, LineJoinStyle);
+no_jsmanaged_fields!(LineCapStyle, LineJoinStyle, CompositionOrBlending);
 
 impl JSTraceable for Box<ScriptChan+Send> {
     #[inline]
diff --git a/components/script/dom/canvasrenderingcontext2d.rs b/components/script/dom/canvasrenderingcontext2d.rs
index 9f3ae840060..f6111739d8b 100644
--- a/components/script/dom/canvasrenderingcontext2d.rs
+++ b/components/script/dom/canvasrenderingcontext2d.rs
@@ -30,7 +30,7 @@ use geom::size::Size2D;
 use canvas::canvas_msg::{CanvasMsg, Canvas2dMsg, CanvasCommonMsg};
 use canvas::canvas_paint_task::{CanvasPaintTask, FillOrStrokeStyle};
 use canvas::canvas_paint_task::{LinearGradientStyle, RadialGradientStyle};
-use canvas::canvas_paint_task::{LineCapStyle, LineJoinStyle};
+use canvas::canvas_paint_task::{LineCapStyle, LineJoinStyle, CompositionOrBlending};
 
 use net_traits::image::base::Image;
 use net_traits::image_cache_task::{ImageResponseMsg, Msg};
@@ -61,6 +61,7 @@ pub struct CanvasRenderingContext2D {
 #[jstraceable]
 struct CanvasContextState {
     global_alpha: f64,
+    global_composition: CompositionOrBlending,
     image_smoothing_enabled: bool,
     stroke_color: RGBA,
     line_width: f64,
@@ -81,6 +82,7 @@ impl CanvasContextState {
         };
         CanvasContextState {
             global_alpha: 1.0,
+            global_composition: CompositionOrBlending::default(),
             image_smoothing_enabled: true,
             stroke_color: black,
             line_width: 1.0,
@@ -421,6 +423,23 @@ impl<'a> CanvasRenderingContext2DMethods for JSRef<'a, CanvasRenderingContext2D>
         self.renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetGlobalAlpha(alpha as f32))).unwrap()
     }
 
+    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalcompositeoperation
+    fn GlobalCompositeOperation(self) -> DOMString {
+        let state = self.state.borrow();
+        match state.global_composition {
+            CompositionOrBlending::Composition(op) => op.to_str().to_owned(),
+            CompositionOrBlending::Blending(op) => op.to_str().to_owned(),
+        }
+    }
+
+    // https://html.spec.whatwg.org/multipage/#dom-context-2d-globalcompositeoperation
+    fn SetGlobalCompositeOperation(self, op_str: DOMString) {
+        if let Some(op) = CompositionOrBlending::from_str(&op_str) {
+            self.state.borrow_mut().global_composition = op;
+            self.renderer.send(CanvasMsg::Canvas2d(Canvas2dMsg::SetGlobalComposition(op))).unwrap()
+        }
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-fillrect
     fn FillRect(self, x: f64, y: f64, width: f64, height: f64) {
         if let Some(rect) = self.create_drawable_rect(x, y, width, height) {
diff --git a/components/script/dom/webidls/CanvasRenderingContext2D.webidl b/components/script/dom/webidls/CanvasRenderingContext2D.webidl
index 268a129003d..447afc745f5 100644
--- a/components/script/dom/webidls/CanvasRenderingContext2D.webidl
+++ b/components/script/dom/webidls/CanvasRenderingContext2D.webidl
@@ -50,7 +50,7 @@ interface CanvasRenderingContext2D {
 
   // compositing
   attribute unrestricted double globalAlpha; // (default 1.0)
-  //         attribute DOMString globalCompositeOperation; // (default source-over)
+  attribute DOMString globalCompositeOperation; // (default source-over)
 
   // image smoothing
            attribute boolean imageSmoothingEnabled; // (default true)