constellation: Make setting up the WebGL state fallible.

This fixes a regression caused by the glutin update.

We now are creating EGL contexts in Linux Wayland, instead of X context, so the
GLContextFactory assumption of one GL back-end per platform is broken.

This just works around it, for now, but in general I think not relying on
available WebGL state is a good thing, and we do that already for WebVR anyway.

8 files changed, 49 insertions, 32 deletions

diff --git a/components/canvas/gl_context.rs b/components/canvas/gl_context.rs
index e0d686f622a..7720f8f678a 100644
--- a/components/canvas/gl_context.rs
+++ b/components/canvas/gl_context.rs
@@ -24,6 +24,9 @@ pub enum GLContextFactory {
 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> {
+        // FIXME(emilio): This assumes a single GL backend per platform which is
+        // not true on Linux, we probably need a third `Egl` variant or abstract
+        // it a bit more...
         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.
diff --git a/components/constellation/constellation.rs b/components/constellation/constellation.rs
index f6a47ba14b1..cdc850495b1 100644
--- a/components/constellation/constellation.rs
+++ b/components/constellation/constellation.rs
@@ -325,7 +325,7 @@ pub struct Constellation<Message, LTF, STF> {
     phantom: PhantomData<(Message, LTF, STF)>,
 
     /// Entry point to create and get channels to a WebGLThread.
-    webgl_threads: WebGLThreads,
+    webgl_threads: Option<WebGLThreads>,
 
     /// A channel through which messages can be sent to the webvr thread.
     webvr_chan: Option<IpcSender<WebVRMsg>>,
@@ -370,7 +370,7 @@ pub struct InitialConstellationState {
     pub webrender_api_sender: webrender_api::RenderApiSender,
 
     /// Entry point to create and get channels to a WebGLThread.
-    pub webgl_threads: WebGLThreads,
+    pub webgl_threads: Option<WebGLThreads>,
 
     /// A channel to the webgl thread.
     pub webvr_chan: Option<IpcSender<WebVRMsg>>,
@@ -740,7 +740,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
             webrender_api_sender: self.webrender_api_sender.clone(),
             webrender_document: self.webrender_document,
             is_private,
-            webgl_chan: self.webgl_threads.pipeline(),
+            webgl_chan: self.webgl_threads.as_ref().map(|threads| threads.pipeline()),
             webvr_chan: self.webvr_chan.clone()
         });
 
@@ -1431,9 +1431,11 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
             }
         }
 
-        debug!("Exiting WebGL thread.");
-        if let Err(e) = self.webgl_threads.exit() {
-            warn!("Exit WebGL Thread failed ({})", e);
+        if let Some(webgl_threads) = self.webgl_threads.as_ref() {
+            debug!("Exiting WebGL thread.");
+            if let Err(e) = webgl_threads.exit() {
+                warn!("Exit WebGL Thread failed ({})", e);
+            }
         }
 
         if let Some(chan) = self.webvr_chan.as_ref() {
diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index 4753f0ba3eb..99603cad805 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -170,8 +170,8 @@ pub struct InitialPipelineState {
     /// Whether this pipeline is considered private.
     pub is_private: bool,
 
-    /// A channel to the webgl thread.
-    pub webgl_chan: WebGLPipeline,
+    /// A channel to the WebGL thread.
+    pub webgl_chan: Option<WebGLPipeline>,
 
     /// A channel to the webvr thread.
     pub webvr_chan: Option<IpcSender<WebVRMsg>>,
@@ -457,7 +457,7 @@ pub struct UnprivilegedPipelineContent {
     script_content_process_shutdown_port: IpcReceiver<()>,
     webrender_api_sender: webrender_api::RenderApiSender,
     webrender_document: webrender_api::DocumentId,
-    webgl_chan: WebGLPipeline,
+    webgl_chan: Option<WebGLPipeline>,
     webvr_chan: Option<IpcSender<WebVRMsg>>,
 }
 
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index fa1015582cf..0aabf2e319a 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -224,8 +224,12 @@ impl WebGLRenderingContext {
             return Err("WebGL context creation error forced by pref `webgl.testing.context_creation_error`".into());
         }
 
+        let webgl_chan = match window.webgl_chan() {
+            Some(chan) => chan,
+            None => return Err("WebGL initialization failed early on".into()),
+        };
+
         let (sender, receiver) = webgl_channel().unwrap();
-        let webgl_chan = window.webgl_chan();
         webgl_chan.send(WebGLMsg::CreateContext(webgl_version, size, attrs, sender))
                   .unwrap();
         let result = receiver.recv().unwrap();
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 2cc1515b735..f6177e90fcf 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -257,9 +257,9 @@ pub struct Window {
 
     test_runner: MutNullableDom<TestRunner>,
 
-    /// A handle for communicating messages to the webvr thread, if available.
+    /// A handle for communicating messages to the WebGL thread, if available.
     #[ignore_malloc_size_of = "channels are hard"]
-    webgl_chan: WebGLChan,
+    webgl_chan: Option<WebGLChan>,
 
     /// A handle for communicating messages to the webvr thread, if available.
     #[ignore_malloc_size_of = "channels are hard"]
@@ -402,7 +402,7 @@ impl Window {
         self.current_viewport.clone().get()
     }
 
-    pub fn webgl_chan(&self) -> WebGLChan {
+    pub fn webgl_chan(&self) -> Option<WebGLChan> {
         self.webgl_chan.clone()
     }
 
@@ -1756,7 +1756,7 @@ impl Window {
         origin: MutableOrigin,
         navigation_start: u64,
         navigation_start_precise: u64,
-        webgl_chan: WebGLChan,
+        webgl_chan: Option<WebGLChan>,
         webvr_chan: Option<IpcSender<WebVRMsg>>,
         microtask_queue: Rc<MicrotaskQueue>,
         webrender_document: DocumentId,
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index f386d29487e..d949e9d0b8c 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -483,8 +483,8 @@ pub struct ScriptThread {
     /// The unit of related similar-origin browsing contexts' list of MutationObserver objects
     mutation_observers: DomRefCell<Vec<Dom<MutationObserver>>>,
 
-    /// A handle to the webgl thread
-    webgl_chan: WebGLPipeline,
+    /// A handle to the WebGL thread
+    webgl_chan: Option<WebGLPipeline>,
 
     /// A handle to the webvr thread, if available
     webvr_chan: Option<IpcSender<WebVRMsg>>,
@@ -2130,7 +2130,7 @@ impl ScriptThread {
             origin,
             incomplete.navigation_start,
             incomplete.navigation_start_precise,
-            self.webgl_chan.channel(),
+            self.webgl_chan.as_ref().map(|chan| chan.channel()),
             self.webvr_chan.clone(),
             self.microtask_queue.clone(),
             self.webrender_document,
diff --git a/components/script_traits/lib.rs b/components/script_traits/lib.rs
index eec50faf09b..46f5ed6c90c 100644
--- a/components/script_traits/lib.rs
+++ b/components/script_traits/lib.rs
@@ -539,8 +539,8 @@ pub struct InitialScriptState {
     pub pipeline_namespace_id: PipelineNamespaceId,
     /// A ping will be sent on this channel once the script thread shuts down.
     pub content_process_shutdown_chan: IpcSender<()>,
-    /// A channel to the webgl thread used in this pipeline.
-    pub webgl_chan: WebGLPipeline,
+    /// A channel to the WebGL thread used in this pipeline.
+    pub webgl_chan: Option<WebGLPipeline>,
     /// A channel to the webvr thread, if available.
     pub webvr_chan: Option<IpcSender<WebVRMsg>>,
     /// The Webrender document ID associated with this thread.
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index 8844625af19..45b6af50c89 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -566,23 +566,31 @@ fn create_constellation(user_agent: Cow<'static, str>,
 
     // GLContext factory used to create WebGL Contexts
     let gl_factory = if opts::get().should_use_osmesa() {
-        GLContextFactory::current_osmesa_handle().unwrap()
+        GLContextFactory::current_osmesa_handle()
     } else {
-        GLContextFactory::current_native_handle(&compositor_proxy).unwrap()
+        GLContextFactory::current_native_handle(&compositor_proxy)
     };
 
     // Initialize WebGL Thread entry point.
-    let (webgl_threads, image_handler, output_handler) = WebGLThreads::new(gl_factory,
-                                                                           window_gl,
-                                                                           webrender_api_sender.clone(),
-                                                                           webvr_compositor.map(|c| c as Box<_>));
-    // Set webrender external image handler for WebGL textures
-    webrender.set_external_image_handler(image_handler);
-
-    // Set DOM to texture handler, if enabled.
-    if let Some(output_handler) = output_handler {
-        webrender.set_output_image_handler(output_handler);
-    }
+    let webgl_threads = gl_factory.map(|factory| {
+        let (webgl_threads, image_handler, output_handler) =
+            WebGLThreads::new(
+                factory,
+                window_gl,
+                webrender_api_sender.clone(),
+                webvr_compositor.map(|c| c as Box<_>),
+            );
+
+        // Set webrender external image handler for WebGL textures
+        webrender.set_external_image_handler(image_handler);
+
+        // Set DOM to texture handler, if enabled.
+        if let Some(output_handler) = output_handler {
+            webrender.set_output_image_handler(output_handler);
+        }
+
+        webgl_threads
+    });
 
     let initial_state = InitialConstellationState {
         compositor_proxy,