Merge pull request #2348 from juj/context_lost

WebGL context loss handling improvements.

4 files changed, 26 insertions, 7 deletions

diff --git a/src/library_browser.js b/src/library_browser.js
index 07d33b32..4ef7c577 100644
--- a/src/library_browser.js
+++ b/src/library_browser.js
@@ -322,11 +322,6 @@ mergeInto(LibraryManager.library, {
 #endif
         // Set the background of the WebGL canvas to black
         canvas.style.backgroundColor = "black";
-
-        // Warn on context loss
-        canvas.addEventListener('webglcontextlost', function(event) {
-          alert('WebGL context lost. You will need to reload the page.');
-        }, false);
       }
       if (setInModule) {
         GLctx = Module.ctx = ctx;
diff --git a/src/library_html5.js b/src/library_html5.js
index d9376c2a..d5d0cd66 100644
--- a/src/library_html5.js
+++ b/src/library_html5.js
@@ -1307,6 +1307,12 @@ var LibraryJSEvents = {
     JSEvents.registerWebGlEventCallback(target, userData, useCapture, callbackfunc, {{{ cDefine('EMSCRIPTEN_EVENT_WEBGLCONTEXTRESTORED') }}}, "webglcontextrestored");
     return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
   },
+
+  emscripten_is_webgl_context_lost: function(target) {
+    // TODO: In the future if multiple GL contexts are supported, use the 'target' parameter to find the canvas to query.
+    if (!Module['ctx']) return true; // No context ~> lost context.
+    return Module['ctx'].isContextLost();
+  }
 };
 
 autoAddDeps(LibraryJSEvents, '$JSEvents');
diff --git a/src/shell.html b/src/shell.html
index 1e213024..d204bfa6 100644
--- a/src/shell.html
+++ b/src/shell.html
@@ -1245,7 +1245,16 @@
             console.error(text);
           }
         },
-        canvas: document.getElementById('canvas'),
+        canvas: (function() {
+          var canvas = document.getElementById('canvas');
+
+          // As a default initial behavior, pop up an alert when webgl context is lost. To make your
+          // application robust, you may want to override this behavior before shipping!
+          // See http://www.khronos.org/registry/webgl/specs/latest/1.0/#5.15.2
+          canvas.addEventListener("webglcontextlost", function(e) { alert('WebGL context lost. You will need to reload the page.'); e.preventDefault(); }, false);
+
+          return canvas;
+        })(),
         setStatus: function(text) {
           if (!Module.setStatus.last) Module.setStatus.last = { time: Date.now(), text: '' };
           if (text === Module.setStatus.text) return;
diff --git a/src/shell_minimal.html b/src/shell_minimal.html
index 7dd67929..b67c6fdd 100644
--- a/src/shell_minimal.html
+++ b/src/shell_minimal.html
@@ -101,7 +101,16 @@
             console.error(text);
           }
         },
-        canvas: document.getElementById('canvas'),
+        canvas: (function() {
+          var canvas = document.getElementById('canvas');
+
+          // As a default initial behavior, pop up an alert when webgl context is lost. To make your
+          // application robust, you may want to override this behavior before shipping!
+          // See http://www.khronos.org/registry/webgl/specs/latest/1.0/#5.15.2
+          canvas.addEventListener("webglcontextlost", function(e) { alert('WebGL context lost. You will need to reload the page.'); e.preventDefault(); }, false);
+
+          return canvas;
+        })(),
         setStatus: function(text) {
           if (!Module.setStatus.last) Module.setStatus.last = { time: Date.now(), text: '' };
           if (text === Module.setStatus.text) return;