Auto merge of #20447 - Brody-Eastwood:master, r=jdm

NCSU Canvas Rendering Project Initial Steps

<!-- Please describe your changes on the following line: -->
Implements the initial steps from:

https://github.com/servo/servo/wiki/Canvas-rendering-project

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/20447)
<!-- Reviewable:end -->

1 files changed, 16 insertions, 2 deletions

diff --git a/components/script/dom/htmlcanvaselement.rs b/components/script/dom/htmlcanvaselement.rs
index 8cfbccd5faa..3854b29967b 100644
--- a/components/script/dom/htmlcanvaselement.rs
+++ b/components/script/dom/htmlcanvaselement.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use base64;
-use canvas_traits::canvas::{CanvasMsg, FromScriptMsg};
+use canvas_traits::canvas::{CanvasMsg, CanvasId, FromScriptMsg};
 use canvas_traits::webgl::WebGLVersion;
 use dom::attr::Attr;
 use dom::bindings::cell::DomRefCell;
@@ -105,6 +105,7 @@ pub trait LayoutHTMLCanvasElementHelpers {
     fn data(&self) -> HTMLCanvasData;
     fn get_width(&self) -> LengthOrPercentageOrAuto;
     fn get_height(&self) -> LengthOrPercentageOrAuto;
+    fn get_canvas_id_for_layout(&self) -> CanvasId;
 }
 
 impl LayoutHTMLCanvasElementHelpers for LayoutDom<HTMLCanvasElement> {
@@ -133,6 +134,7 @@ impl LayoutHTMLCanvasElementHelpers for LayoutDom<HTMLCanvasElement> {
                 source: source,
                 width: width_attr.map_or(DEFAULT_WIDTH, |val| val.as_uint()),
                 height: height_attr.map_or(DEFAULT_HEIGHT, |val| val.as_uint()),
+                canvas_id: self.get_canvas_id_for_layout(),
             }
         }
     }
@@ -156,6 +158,18 @@ impl LayoutHTMLCanvasElementHelpers for LayoutDom<HTMLCanvasElement> {
                 .unwrap_or(LengthOrPercentageOrAuto::Auto)
         }
     }
+
+    #[allow(unsafe_code)]
+    fn get_canvas_id_for_layout(&self) -> CanvasId {
+        unsafe {
+            let canvas = &*self.unsafe_get();
+            if let &Some(CanvasContext::Context2d(ref context)) = canvas.context.borrow_for_layout() {
+                context.to_layout().get_canvas_id()
+            } else {
+                CanvasId(0)
+            }
+        }
+    }
 }
 
 
@@ -261,7 +275,7 @@ impl HTMLCanvasElement {
         let data = match self.context.borrow().as_ref() {
             Some(&CanvasContext::Context2d(ref context)) => {
                 let (sender, receiver) = ipc::channel(self.global().time_profiler_chan().clone()).unwrap();
-                let msg = CanvasMsg::FromScript(FromScriptMsg::SendPixels(sender));
+                let msg = CanvasMsg::FromScript(FromScriptMsg::SendPixels(sender), context.get_canvas_id());
                 context.get_ipc_renderer().send(msg).unwrap();
 
                 receiver.recv().unwrap()?.into()