Implementation of 2D canvas context lost/restored events

LayoutTests/fast/canvas/script-tests/canvas-lost-gpu-context.js

 description("Test the behavior of canvas recovery after a gpu context loss");
 
-var recoveryLoopPeriod = 5;
 var ctx;
-var imageData;
-var imgdata;
+var lostEventHasFired = false;
+var contextLostTest;
 
 if (window.internals && window.testRunner) {
     testRunner.dumpAsText();
-    ctx = document.createElement('canvas').getContext('2d');
+    var canvas = document.createElement('canvas');
+    canvas.addEventListener('contextlost', contextLost);
+    canvas.addEventListener('contextrestored', contextRestored);
+    ctx = canvas.getContext('2d');
     document.body.appendChild(ctx.canvas);
-    ctx.fillStyle = '#f00';
-    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
-    imageData = ctx.getImageData(0, 0, 1, 1);
-    imgdata = imageData.data;
-    shouldBe("imgdata[0]", "255");
-    shouldBe("imgdata[1]", "0");
-    shouldBe("imgdata[2]", "0");
-    shouldBe("imgdata[3]", "255");
-
+    verifyContextLost(false);
     window.internals.loseSharedGraphicsContext3D();
-    // Verify whether canvas contents are lost with the graphics context.
-    imageData = ctx.getImageData(0, 0, 1, 1);
-    if (imageData.data[0] == 255) {
+    // for the canvas to realize it Graphics context was lost we must try to use the canvas
+    ctx.fillRect(0, 0, 1, 1);
+    if (!ctx.isContextLost()) {
         debug('<span>Aborting test: Graphics context loss did not destroy canvas contents. This is expected if canvas is not accelerated.</span>');
     } else {
-        // Redrawing immediately will fail because we are working with an
-        // unrecovered context here. The context recovery is asynchronous
-        // because it requires the context loss notification task to be
-        // processed on the renderer main thread, which triggers the
-        // re-creation of the SharedGC3D.
-        ctx.fillStyle = '#0f0';
-        ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
-        imageData = ctx.getImageData(0, 0, 1, 1);
-        imgdata = imageData.data;
-        shouldBe("imgdata[0]", "0");
-        shouldBe("imgdata[1]", "0");
-        shouldBe("imgdata[2]", "0");
-        shouldBe("imgdata[3]", "0");
-
+        verifyContextLost(true);
         testRunner.waitUntilDone();
-        setTimeout(recoveryLoop, recoveryLoopPeriod);
     }
 } else {
     testFailed('This test requires window.internals and window.testRunner.');
 }
 
-// Graphics context recovery happens asynchronously.  To test for recovery, we keep
-// retrying to use the canvas until it succeeds, which should hapen long before the test
-// times-out.
-function recoveryLoop() {
-    ctx.fillStyle = '#00f';
-    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
-    imageData = ctx.getImageData(0, 0, 1, 1);
-    if (imageData.data[2] == 255) {
-        testPassed('Graphics context recovered.');
-        testRunner.notifyDone();
+
+function verifyContextLost(shouldBeLost) {
+    // Verify context loss experimentally as well as isContextLost()
+    ctx.fillStyle = '#0f0';
+    ctx.fillRect(0, 0, 1, 1);
+    contextLostTest = ctx.getImageData(0, 0, 1, 1).data[1] == 0;
+    if (shouldBeLost) {
+        shouldBeTrue('contextLostTest');
+        shouldBeTrue('ctx.isContextLost()');
     } else {
-        // Context not yet recovered.  Try again.
-        setTimeout(recoveryLoop, recoveryLoopPeriod);
+        shouldBeFalse('contextLostTest');
+        shouldBeFalse('ctx.isContextLost()');
     }
 }
+
+function contextLost() {
+    if (lostEventHasFired) {
+        testFailed('Context lost event was dispatched more than once.');
+    } else {
+        testPassed('Graphics context lost event dispatched.');
+    }
+    lostEventHasFired = true;
+    verifyContextLost(true);
+}
+
+function contextRestored() {
+    if (lostEventHasFired) {
+        testPassed('Context restored event dispatched after context lost.');
+    } else {
+        testFailed('Context restored event was dispatched before a context lost event.');
+    }
+    verifyContextLost(false);
+    testRunner.notifyDone();
+}