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

Improved WebGL architecture

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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.

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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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1 files changed, 203 insertions, 0 deletions

diff --git a/components/canvas/gl_context.rs b/components/canvas/gl_context.rs
new file mode 100644
index 00000000000..69a26c0e03c
--- /dev/null
+++ b/components/canvas/gl_context.rs
@@ -0,0 +1,203 @@
+/* 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 canvas_traits::webgl::WebGLCommand;
+use compositing::compositor_thread::{CompositorProxy, self};
+use euclid::Size2D;
+use gleam::gl;
+use offscreen_gl_context::{ColorAttachmentType, GLContext, GLContextAttributes, GLContextDispatcher, GLLimits};
+use offscreen_gl_context::{NativeGLContext, NativeGLContextHandle, NativeGLContextMethods};
+use offscreen_gl_context::{OSMesaContext, OSMesaContextHandle};
+use std::sync::{Arc, Mutex};
+use super::webgl_thread::WebGLImpl;
+
+/// The GLContextFactory is used to create shared GL contexts with the main thread GL context.
+/// Currently, shared textures are used to render WebGL textures into the WR compositor.
+/// In order to create a shared context, the GLContextFactory stores the handle of the main GL context.
+pub enum GLContextFactory {
+    Native(NativeGLContextHandle, Option<MainThreadDispatcher>),
+    OSMesa(OSMesaContextHandle),
+}
+
+impl GLContextFactory {
+    /// Creates a new GLContextFactory that uses the currently bound GL context to create shared contexts.
+    pub fn current_native_handle(proxy: &CompositorProxy) -> Option<GLContextFactory> {
+        NativeGLContext::current_handle().map(|handle| {
+            if cfg!(target_os = "windows") {
+                // Used to dispatch functions from the GLContext thread to the main thread's event loop.
+                // Required to allow WGL GLContext sharing in Windows.
+                GLContextFactory::Native(handle, Some(MainThreadDispatcher::new(proxy.clone_compositor_proxy())))
+            } else {
+                GLContextFactory::Native(handle, None)
+            }
+        })
+    }
+
+    /// Creates a new GLContextFactory that uses the currently bound OSMesa context to create shared contexts.
+    pub fn current_osmesa_handle() -> Option<GLContextFactory> {
+        OSMesaContext::current_handle().map(GLContextFactory::OSMesa)
+    }
+
+    /// Creates a new shared GLContext with the main GLContext
+    pub fn new_shared_context(&self,
+                              size: Size2D<i32>,
+                              attributes: GLContextAttributes) -> Result<GLContextWrapper, &'static str> {
+        match *self {
+            GLContextFactory::Native(ref handle, ref dispatcher) => {
+                let dispatcher = dispatcher.as_ref().map(|d| Box::new(d.clone()) as Box<_>);
+                let ctx = GLContext::<NativeGLContext>::new_shared_with_dispatcher(size,
+                                                                                   attributes,
+                                                                                   ColorAttachmentType::Texture,
+                                                                                   gl::GlType::default(),
+                                                                                   Some(handle),
+                                                                                   dispatcher);
+                ctx.map(GLContextWrapper::Native)
+            }
+            GLContextFactory::OSMesa(ref handle) => {
+                let ctx = GLContext::<OSMesaContext>::new_shared_with_dispatcher(size.to_untyped(),
+                                                                                 attributes,
+                                                                                 ColorAttachmentType::Texture,
+                                                                                 gl::GlType::default(),
+                                                                                 Some(handle),
+                                                                                 None);
+                ctx.map(GLContextWrapper::OSMesa)
+            }
+        }
+    }
+
+    /// Creates a new non-shared GLContext
+    pub fn new_context(&self,
+                       size: Size2D<i32>,
+                       attributes: GLContextAttributes) -> Result<GLContextWrapper, &'static str> {
+        match *self {
+            GLContextFactory::Native(..) => {
+                let ctx = GLContext::<NativeGLContext>::new_shared_with_dispatcher(size,
+                                                                                   attributes,
+                                                                                   ColorAttachmentType::Texture,
+                                                                                   gl::GlType::default(),
+                                                                                   None,
+                                                                                   None);
+                ctx.map(GLContextWrapper::Native)
+            }
+            GLContextFactory::OSMesa(_) => {
+                let ctx = GLContext::<OSMesaContext>::new_shared_with_dispatcher(size.to_untyped(),
+                                                                                 attributes,
+                                                                                 ColorAttachmentType::Texture,
+                                                                                 gl::GlType::default(),
+                                                                                 None,
+                                                                                 None);
+                ctx.map(GLContextWrapper::OSMesa)
+            }
+        }
+    }
+}
+
+
+/// GLContextWrapper used to abstract NativeGLContext and OSMesaContext types
+pub enum GLContextWrapper {
+    Native(GLContext<NativeGLContext>),
+    OSMesa(GLContext<OSMesaContext>),
+}
+
+impl GLContextWrapper {
+    pub fn make_current(&self) {
+        match *self {
+            GLContextWrapper::Native(ref ctx) => {
+                ctx.make_current().unwrap();
+            }
+            GLContextWrapper::OSMesa(ref ctx) => {
+                ctx.make_current().unwrap();
+            }
+        }
+    }
+
+    pub fn unbind(&self) {
+        match *self {
+            GLContextWrapper::Native(ref ctx) => {
+                ctx.unbind().unwrap();
+            }
+            GLContextWrapper::OSMesa(ref ctx) => {
+                ctx.unbind().unwrap();
+            }
+        }
+    }
+
+    pub fn apply_command(&self, cmd: WebGLCommand) {
+        match *self {
+            GLContextWrapper::Native(ref ctx) => {
+                WebGLImpl::apply(ctx, cmd);
+            }
+            GLContextWrapper::OSMesa(ref ctx) => {
+                WebGLImpl::apply(ctx, cmd);
+            }
+        }
+    }
+
+    pub fn gl(&self) -> &gl::Gl {
+        match *self {
+            GLContextWrapper::Native(ref ctx) => {
+                ctx.gl()
+            }
+            GLContextWrapper::OSMesa(ref ctx) => {
+                ctx.gl()
+            }
+        }
+    }
+
+    pub fn get_info(&self) -> (Size2D<i32>, u32, GLLimits) {
+        match *self {
+            GLContextWrapper::Native(ref ctx) => {
+                let (real_size, texture_id) = {
+                    let draw_buffer = ctx.borrow_draw_buffer().unwrap();
+                    (draw_buffer.size(), draw_buffer.get_bound_texture_id().unwrap())
+                };
+
+                let limits = ctx.borrow_limits().clone();
+
+                (real_size, texture_id, limits)
+            }
+            GLContextWrapper::OSMesa(ref ctx) => {
+                let (real_size, texture_id) = {
+                    let draw_buffer = ctx.borrow_draw_buffer().unwrap();
+                    (draw_buffer.size(), draw_buffer.get_bound_texture_id().unwrap())
+                };
+
+                let limits = ctx.borrow_limits().clone();
+
+                (real_size, texture_id, limits)
+            }
+        }
+    }
+
+    pub fn resize(&mut self, size: Size2D<i32>) -> Result<(), &'static str> {
+        match *self {
+            GLContextWrapper::Native(ref mut ctx) => {
+                ctx.resize(size)
+            }
+            GLContextWrapper::OSMesa(ref mut ctx) => {
+                ctx.resize(size)
+            }
+        }
+    }
+}
+
+/// Implements GLContextDispatcher to dispatch functions from GLContext threads to the main thread's event loop.
+/// It's used in Windows to allow WGL GLContext sharing.
+#[derive(Clone)]
+pub struct MainThreadDispatcher {
+    compositor_proxy: Arc<Mutex<CompositorProxy>>
+}
+
+impl MainThreadDispatcher {
+    fn new(proxy: CompositorProxy) -> Self {
+        Self {
+            compositor_proxy: Arc::new(Mutex::new(proxy)),
+        }
+    }
+}
+impl GLContextDispatcher for MainThreadDispatcher {
+    fn dispatch(&self, f: Box<Fn() + Send>) {
+        self.compositor_proxy.lock().unwrap().send(compositor_thread::Msg::Dispatch(f));
+    }
+}