Auto merge of #17891 - MortimerGoro:webgl_move, r=glennw,emilio

Improved WebGL architecture

<!-- Please describe your changes on the following line: -->

Info about the big picture and the goals of the WebGL refactor in this thread: https://groups.google.com/forum/#!topic/mozilla.dev.servo/0WMGz60kKzQ

I tried to reduce this PR as much as possible as requested in the thread. I'll do separate PRs for other features (e.g.: Batch messages or use shared memory to improve frame times) or fixes.

Some tips to ease the review process:
- Most changes in DOM objects follow the same pattern (remove CanvasMsg wrapper and use the new sender method).
- WebGLCommands are the same ones as before (moved from webrender_api). So those lines are already reviewed.
- See WebGL traits in [components/canvas_traits/webgl.rs](https://github.com/servo/servo/pull/17891/files#diff-8701045d01505418701d0631d4d45562)
- See WebGLThread and WR External Image bridge in [components/canvas/webgl_thread.rs](https://github.com/servo/servo/pull/17891/files#diff-281554879f39a2a041f7a69d442a5d2e)
- The implementation submitted in this PR creates a single `WebGLThread` for all ScriptThread/Pipelines. See that in [components/canvas/webgl_mode/inprocess.rs](https://github.com/servo/servo/pull/17891/files#diff-250070c6c5a38c7f9fa0f5b3c101f68b)

The conformance tests will help to guarantee that we don't miss anything.

---
<!-- 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/17891)
<!-- Reviewable:end -->

2 files changed, 101 insertions, 0 deletions

diff --git a/components/canvas/webgl_mode/inprocess.rs b/components/canvas/webgl_mode/inprocess.rs
new file mode 100644
index 00000000000..257f1395545
--- /dev/null
+++ b/components/canvas/webgl_mode/inprocess.rs
@@ -0,0 +1,95 @@
+/* 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 ::gl_context::GLContextFactory;
+use ::webgl_thread::{WebGLExternalImageApi, WebGLExternalImageHandler, WebGLThreadObserver, WebGLThread};
+use canvas_traits::webgl::{WebGLChan, WebGLContextId, WebGLMsg, WebGLPipeline, WebGLReceiver};
+use canvas_traits::webgl::{WebGLSender, WebVRCommand, WebVRRenderHandler};
+use canvas_traits::webgl::webgl_channel;
+use euclid::Size2D;
+use std::marker::PhantomData;
+use webrender;
+use webrender_api;
+
+/// WebGL Threading API entry point that lives in the constellation.
+pub struct WebGLThreads(WebGLSender<WebGLMsg>);
+
+impl WebGLThreads {
+    /// Creates a new WebGLThreads object
+    pub fn new(gl_factory: GLContextFactory,
+               webrender_api_sender: webrender_api::RenderApiSender,
+               webvr_compositor: Option<Box<WebVRRenderHandler>>)
+               -> (WebGLThreads, Box<webrender::ExternalImageHandler>) {
+        // This implementation creates a single `WebGLThread` for all the pipelines.
+        let channel = WebGLThread::start(gl_factory,
+                                         webrender_api_sender,
+                                         webvr_compositor.map(|c| WebVRRenderWrapper(c)),
+                                         PhantomData);
+        let external = WebGLExternalImageHandler::new(WebGLExternalImages::new(channel.clone()));
+        (WebGLThreads(channel), Box::new(external))
+    }
+
+    /// Gets the WebGLThread handle for each script pipeline.
+    pub fn pipeline(&self) -> WebGLPipeline {
+        // This mode creates a single thread, so the existing WebGLChan is just cloned.
+        WebGLPipeline(WebGLChan(self.0.clone()))
+    }
+
+    /// Sends a exit message to close the WebGLThreads and release all WebGLContexts.
+    pub fn exit(&self) -> Result<(), &'static str> {
+        self.0.send(WebGLMsg::Exit).map_err(|_| "Failed to send Exit message")
+    }
+}
+
+/// Bridge between the webrender::ExternalImage callbacks and the WebGLThreads.
+struct WebGLExternalImages {
+    webgl_channel: WebGLSender<WebGLMsg>,
+    // Used to avoid creating a new channel on each received WebRender request.
+    lock_channel: (WebGLSender<(u32, Size2D<i32>)>, WebGLReceiver<(u32, Size2D<i32>)>),
+}
+
+impl WebGLExternalImages {
+    fn new(channel: WebGLSender<WebGLMsg>) -> Self {
+        Self {
+            webgl_channel: channel,
+            lock_channel: webgl_channel().unwrap(),
+        }
+    }
+}
+
+impl WebGLExternalImageApi for WebGLExternalImages {
+    fn lock(&mut self, ctx_id: WebGLContextId) -> (u32, Size2D<i32>) {
+        self.webgl_channel.send(WebGLMsg::Lock(ctx_id, self.lock_channel.0.clone())).unwrap();
+        self.lock_channel.1.recv().unwrap()
+    }
+
+    fn unlock(&mut self, ctx_id: WebGLContextId) {
+        self.webgl_channel.send(WebGLMsg::Unlock(ctx_id)).unwrap();
+    }
+}
+
+/// Custom observer used in a `WebGLThread`.
+impl WebGLThreadObserver for PhantomData<()> {
+    fn on_context_create(&mut self, ctx_id: WebGLContextId, texture_id: u32, size: Size2D<i32>) {
+        debug!("WebGLContext created (ctx_id: {:?} texture_id: {:?} size: {:?}", ctx_id, texture_id, size);
+    }
+
+    fn on_context_resize(&mut self, ctx_id: WebGLContextId, texture_id: u32, size: Size2D<i32>) {
+        debug!("WebGLContext resized (ctx_id: {:?} texture_id: {:?} size: {:?}", ctx_id, texture_id, size);
+    }
+
+    fn on_context_delete(&mut self, ctx_id: WebGLContextId) {
+        debug!("WebGLContext deleted (ctx_id: {:?})", ctx_id);
+    }
+}
+
+
+/// Wrapper to send WebVR commands used in `WebGLThread`.
+struct WebVRRenderWrapper(Box<WebVRRenderHandler>);
+
+impl WebVRRenderHandler for WebVRRenderWrapper {
+    fn handle(&mut self, command: WebVRCommand, texture: Option<(u32, Size2D<i32>)>) {
+        self.0.handle(command, texture);
+    }
+}
diff --git a/components/canvas/webgl_mode/mod.rs b/components/canvas/webgl_mode/mod.rs
new file mode 100644
index 00000000000..660818fb096
--- /dev/null
+++ b/components/canvas/webgl_mode/mod.rs
@@ -0,0 +1,6 @@
+/* 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/. */
+
+mod inprocess;
+pub use self::inprocess::WebGLThreads;