Skip drawing while the GL context reports it is lost

src/RenderWebGL.js

@@ -968,7 +968,7 @@ class RenderWebGL extends EventEmitter {
      * @returns {boolean} True while the WebGL context is lost and nothing can be drawn.
      */
     get isContextLost () {
-        return this._contextLost;
+        return this._contextLost || this._gl.isContextLost();
     }
 
     /**
@@ -1011,7 +1011,7 @@ class RenderWebGL extends EventEmitter {
     }
 
     draw() {
-        if (!this.dirty || this._contextLost) {
+        if (!this.dirty || this.isContextLost) {
             return;
         }
         this.dirty = false;

test/unit/ContextLossTests.js

@@ -10,7 +10,9 @@ const fakeRenderer = () => {
     renderer._allDrawables = [];
     renderer._drawList = [];
     renderer._contextLost = false;
-    renderer._gl = {};
+    renderer._gl = {
+        isContextLost: () => false
+    };
     renderer.dirty = true;
     renderer._listeners = {};
     renderer.emit = name => {
@@ -39,6 +41,19 @@ test('losing the context stops drawing and asks the browser to restore it', t =>
     t.end();
 });
 
+test('a context the browser has lost is not drawn before the lost event arrives', t => {
+    const renderer = fakeRenderer();
+    renderer._gl.isContextLost = () => true;
+    t.equal(renderer.isContextLost, true);
+
+    renderer._doExitDrawRegion = () => {
+        throw new Error('draw must not touch GL while the context is lost');
+    };
+    t.doesNotThrow(() => renderer.draw());
+    t.equal(renderer.dirty, true, 'the frame is still pending');
+    t.end();
+});
+
 test('restoring the context rebuilds renderer resources and tells every skin', t => {
     const renderer = fakeRenderer();
     renderer._contextLost = true;