1 files changed, 32 insertions, 6 deletions
diff --git a/src/shell.html b/src/shell.html
index c096a314..95ab5a6a 100644
--- a/src/shell.html
+++ b/src/shell.html
@@ -19,12 +19,38 @@
         })(),
         canvas: document.getElementById('canvas')
       };
-      try {
-        Module.ctx2D = Module.canvas.getContext('2d');
-        if (!Module.ctx2D) throw 'Could not create canvas :(';
-      } catch (e) {
-        Module.print('(canvas not available)');
-      }
+      // Define the 2D and WebGL contexts lazily, because a canvas can only
+      // have one context type.
+      Module.__defineGetter__("ctx2D", function() {
+        try {
+          var ctx = Module.canvas.getContext('2d');
+          if (!ctx) throw 'Could not create canvas :(';
+          delete Module["ctxGL"];
+          Module.__defineGetter__("ctxGL", function() {
+            throw 'Could not create a WebGL context for a 2D canvas :(';
+          });
+          delete Module["ctx2D"];
+          return Module["ctx2D"] = ctx;
+        } catch (e) {
+          Module.print('(canvas not available)');
+          return null;
+        }
+      });
+      Module.__defineGetter__("ctxGL", function() {
+        try {
+          var ctx = Module.canvas.getContext('experimental-webgl');
+          if (!ctx) throw 'Could not create canvas :(';
+          delete Module["ctx2D"];
+          Module.__defineGetter__("ctx2D", function() {
+            throw 'Could not create a 2D context for a WebGL canvas :(';
+          });
+          delete Module["ctxGL"];
+          return Module["ctxGL"] = ctx;
+        } catch (e) {
+          Module.print('(canvas not available)');
+          return null;
+        }
+      });
 
       // The compiled code
       {{{ SCRIPT_CODE }}}