From e5892989caf418fe2b9990c61d19de55c47baf55 Mon Sep 17 00:00:00 2001
From: Josh Matthews <josh@joshmatthews.net>
Date: Thu, 27 Sep 2018 18:44:02 -0400
Subject: [PATCH] Warn when using slow WebGL code path.

---
 components/canvas/webgl_thread.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/components/canvas/webgl_thread.rs b/components/canvas/webgl_thread.rs
index 9256692599a..682993cefd3 100644
--- a/components/canvas/webgl_thread.rs
+++ b/components/canvas/webgl_thread.rs
@@ -220,7 +220,9 @@ impl<VR: WebVRRenderHandler + 'static> WebGLThread<VR> {
         // Fallback to readback mode if the shared context creation fails.
         let result = self.gl_factory.new_shared_context(version, size, attributes)
                                     .map(|r| (r, WebGLContextShareMode::SharedTexture))
-                                    .or_else(|_| {
+                                    .or_else(|err| {
+                                        warn!("Couldn't create shared GL context ({}), using slow \
+                                               readback context instead.", err); 
                                         let ctx = self.gl_factory.new_context(version, size, attributes);
                                         ctx.map(|r| (r, WebGLContextShareMode::Readback))
                                     });