diff --git a/dom/canvas/test/mochitest.ini b/dom/canvas/test/mochitest.ini
index ffee4bbb26d..12b23e2df38 100644
--- a/dom/canvas/test/mochitest.ini
+++ b/dom/canvas/test/mochitest.ini
@@ -27,6 +27,9 @@ support-files =
   imagebitmap_on_worker.js
   imagebitmap_structuredclone.js
   imagebitmap_structuredclone_iframe.html
+  offscreencanvas.js
+  offscreencanvas_neuter.js
+  offscreencanvas_serviceworker_inner.html
 
 [test_2d.clearRect.image.offscreen.html]
 [test_2d.clip.winding.html]
@@ -261,3 +264,18 @@ skip-if = (buildapp == 'b2g' && toolkit != 'gonk') # bug 1040965
 [test_createPattern_broken.html]
 [test_setlinedash.html]
 [test_filter.html]
+[test_offscreencanvas_basic_webgl.html]
+tags = offscreencanvas
+[test_offscreencanvas_sharedworker.html]
+tags = offscreencanvas
+[test_offscreencanvas_serviceworker.html]
+tags = offscreencanvas
+skip-if = buildapp == 'b2g'
+[test_offscreencanvas_neuter.html]
+tags = offscreencanvas
+[test_offscreencanvas_many.html]
+tags = offscreencanvas
+[test_offscreencanvas_sizechange.html]
+tags = offscreencanvas
+[test_offscreencanvas_subworker.html]
+tags = offscreencanvas
diff --git a/dom/canvas/test/offscreencanvas.js b/dom/canvas/test/offscreencanvas.js
new file mode 100644
index 00000000000..584954c3ef7
--- /dev/null
+++ b/dom/canvas/test/offscreencanvas.js
@@ -0,0 +1,274 @@
+/* WebWorker for test_offscreencanvas_*.html */
+var port = null;
+
+function ok(expect, msg) {
+  if (port) {
+    port.postMessage({type: "test", result: !!expect, name: msg});
+  } else {
+    postMessage({type: "test", result: !!expect, name: msg});
+  }
+}
+
+function finish() {
+  if (port) {
+    port.postMessage({type: "finish"});
+  } else {
+    postMessage({type: "finish"});
+  }
+}
+
+//--------------------------------------------------------------------
+// WebGL Drawing Functions
+//--------------------------------------------------------------------
+function createDrawFunc(canvas) {
+  var gl;
+
+  try {
+    gl = canvas.getContext("experimental-webgl");
+  } catch (e) {}
+
+  if (!gl) {
+    ok(false, "WebGL is unavailable");
+    return null;
+  }
+
+  var vertSrc = "attribute vec2 position; \
+                 void main(void) { \
+                   gl_Position = vec4(position, 0.0, 1.0); \
+                 }";
+
+  var fragSrc = "precision mediump float; \
+                 void main(void) { \
+                   gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0); \
+                 }";
+
+  // Returns a valid shader, or null on errors.
+  var createShader = function(src, t) {
+    var shader = gl.createShader(t);
+
+    gl.shaderSource(shader, src);
+    gl.compileShader(shader);
+
+    return shader;
+  };
+
+  var createProgram = function(vsSrc, fsSrc) {
+    var vs = createShader(vsSrc, gl.VERTEX_SHADER);
+    var fs = createShader(fsSrc, gl.FRAGMENT_SHADER);
+
+    var prog = gl.createProgram();
+    gl.attachShader(prog, vs);
+    gl.attachShader(prog, fs);
+    gl.linkProgram(prog);
+
+    if (!gl.getProgramParameter(prog, gl.LINK_STATUS)) {
+      var str = "Shader program linking failed:";
+      str += "\nShader program info log:\n" + gl.getProgramInfoLog(prog);
+      str += "\n\nVert shader log:\n" + gl.getShaderInfoLog(vs);
+      str += "\n\nFrag shader log:\n" + gl.getShaderInfoLog(fs);
+      console.log(str);
+      ok(false, "Shader program linking failed");
+      return null;
+    }
+
+    return prog;
+  };
+
+  gl.disable(gl.DEPTH_TEST);
+
+  var program = createProgram(vertSrc, fragSrc);
+  ok(program, "Creating shader program");
+
+  program.positionAttr = gl.getAttribLocation(program, "position");
+  ok(program.positionAttr >= 0, "position attribute should be valid");
+
+  var vertCoordArr = new Float32Array([
+    -1, -1,
+     1, -1,
+    -1,  1,
+     1,  1,
+  ]);
+  var vertCoordBuff = gl.createBuffer();
+  gl.bindBuffer(gl.ARRAY_BUFFER, vertCoordBuff);
+  gl.bufferData(gl.ARRAY_BUFFER, vertCoordArr, gl.STATIC_DRAW);
+
+  var checkGLError = function(prefix, refValue) {
+    if (!refValue) {
+      refValue = 0;
+    }
+
+    var error = gl.getError();
+    ok(error == refValue,
+         prefix + 'gl.getError should be 0x' + refValue.toString(16) +
+         ', was 0x' + error.toString(16) + '.');
+  };
+
+  var testPixel = function(x, y, refData, infoString) {
+    var pixel = new Uint8Array(4);
+    gl.readPixels(x, y, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
+
+    var pixelMatches = pixel[0] == refData[0] &&
+                       pixel[1] == refData[1] &&
+                       pixel[2] == refData[2] &&
+                       pixel[3] == refData[3];
+    ok(pixelMatches, infoString);
+  };
+
+  var preDraw = function(prefix) {
+    gl.clearColor(1.0, 0.0, 0.0, 1.0);
+    gl.clear(gl.COLOR_BUFFER_BIT);
+
+    testPixel(0, 0, [255, 0, 0, 255], prefix + 'Should be red before drawing.');
+  };
+
+  var postDraw = function(prefix) {
+    testPixel(0, 0, [0, 255, 0, 255], prefix + 'Should be green after drawing.');
+  };
+
+  gl.useProgram(program);
+  gl.enableVertexAttribArray(program.position);
+  gl.vertexAttribPointer(program.position, 2, gl.FLOAT, false, 0, 0);
+
+  // Start drawing
+  checkGLError('after setup');
+
+  return function(prefix) {
+    if (prefix) {
+      prefix = "[" + prefix + "] ";
+    } else {
+      prefix = "";
+    }
+
+    gl.viewport(0, 0, canvas.width, canvas.height);
+
+    preDraw(prefix);
+    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
+    postDraw(prefix);
+    checkGLError(prefix);
+  };
+}
+
+/* entry point */
+function entryFunction(testStr, subtests, offscreenCanvas) {
+  var test = testStr;
+  var canvas = offscreenCanvas;
+
+  if (test != "subworker") {
+    ok(canvas, "Canvas successfully transfered to worker");
+    ok(canvas.getContext, "Canvas has getContext");
+
+    ok(canvas.width == 64, "OffscreenCanvas width should be 64");
+    ok(canvas.height == 64, "OffscreenCanvas height should be 64");
+  }
+
+  var draw;
+
+  //------------------------------------------------------------------------
+  // Basic WebGL test
+  //------------------------------------------------------------------------
+  if (test == "webgl") {
+    draw = createDrawFunc(canvas);
+    if (!draw) {
+      finish();
+      return;
+    }
+
+    var count = 0;
+    var iid = setInterval(function() {
+      if (count++ > 20) {
+        clearInterval(iid);
+        ok(true, "Worker is done");
+        finish();
+        return;
+      }
+      draw("loop " +count);
+    }, 0);
+  }
+  //------------------------------------------------------------------------
+  // Canvas Size Change from Worker
+  //------------------------------------------------------------------------
+  else if (test == "webgl_changesize") {
+    draw = createDrawFunc(canvas);
+    if (!draw) {
+      finish();
+      return;
+    }
+
+    draw("64x64");
+
+    setTimeout(function() {
+      canvas.width = 128;
+      canvas.height = 128;
+      draw("Increased to 128x128");
+
+      setTimeout(function() {
+        canvas.width = 32;
+        canvas.width = 32;
+        draw("Decreased to 32x32");
+
+        setTimeout(function() {
+          canvas.width = 64;
+          canvas.height = 64;
+          draw("Increased to 64x64");
+
+          ok(true, "Worker is done");
+          finish();
+        }, 0);
+      }, 0);
+    }, 0);
+  }
+  //------------------------------------------------------------------------
+  // Using OffscreenCanvas from sub workers
+  //------------------------------------------------------------------------
+  else if (test == "subworker") {
+    /* subworker tests take a list of tests to run on children */
+    var stillRunning = 0;
+    subtests.forEach(function (subtest) {
+      ++stillRunning;
+      var subworker = new Worker('offscreencanvas.js');
+      subworker.onmessage = function(evt) {
+        /* report finish to parent when all children are finished */
+        if (evt.data.type == "finish") {
+          subworker.terminate();
+          if (--stillRunning == 0) {
+            ok(true, "Worker is done");
+            finish();
+          }
+          return;
+        }
+        /* relay all other messages to parent */
+        postMessage(evt.data);
+      };
+
+      var findTransferables = function(t) {
+        if (t.test == "subworker") {
+          var result = [];
+          t.subtests.forEach(function(test) {
+            result = result.concat(findTransferables(test));
+          });
+
+          return result;
+        } else {
+          return [t.canvas];
+        }
+      };
+
+      subworker.postMessage(subtest, findTransferables(subtest));
+    });
+  }
+};
+
+onmessage = function(evt) {
+  port = evt.ports[0];
+  entryFunction(evt.data.test, evt.data.subtests, evt.data.canvas);
+};
+
+onconnect = function(evt) {
+  port = evt.ports[0];
+
+  port.addEventListener('message', function(evt) {
+    entryFunction(evt.data.test, evt.data.subtests, evt.data.canvas);
+  });
+
+  port.start();
+};
diff --git a/dom/canvas/test/offscreencanvas_neuter.js b/dom/canvas/test/offscreencanvas_neuter.js
new file mode 100644
index 00000000000..30648d740a1
--- /dev/null
+++ b/dom/canvas/test/offscreencanvas_neuter.js
@@ -0,0 +1 @@
+/* empty worker for test_offscreencanvas_disable.html */
diff --git a/dom/canvas/test/offscreencanvas_serviceworker_inner.html b/dom/canvas/test/offscreencanvas_serviceworker_inner.html
new file mode 100644
index 00000000000..b153f9524a1
--- /dev/null
+++ b/dom/canvas/test/offscreencanvas_serviceworker_inner.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+</head>
+<body>
+<canvas id="c" width="64" height="64"></canvas>
+<script>
+function ok(expect, msg) {
+  parent.postMessage({type: "test", result: !!expect, name: msg}, "*");
+}
+
+var htmlCanvas = document.getElementById("c");
+
+ok(htmlCanvas, "Should have HTML canvas element");
+
+var messageChannel = new MessageChannel();
+messageChannel.port1.onmessage = function(evt) {
+  parent.postMessage(evt.data, "*");
+}
+
+ok(htmlCanvas.transferControlToOffscreen, "HTMLCanvasElement has transferControlToOffscreen function");
+
+var offscreenCanvas = htmlCanvas.transferControlToOffscreen();
+ok(offscreenCanvas, "Expected transferControlToOffscreen to succeed");
+
+navigator.serviceWorker.ready.then(function() {
+  navigator.serviceWorker.controller.postMessage({test: 'webgl', canvas: offscreenCanvas}, [offscreenCanvas, messageChannel.port2]);
+});
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_basic_webgl.html b/dom/canvas/test/test_offscreencanvas_basic_webgl.html
new file mode 100644
index 00000000000..dd3ac21e748
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_basic_webgl.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<canvas id="c" width="64" height="64"></canvas>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+
+  var htmlCanvas = document.getElementById("c");
+  var worker = new Worker("offscreencanvas.js");
+
+  ok(htmlCanvas, "Should have HTML canvas element");
+  ok(worker, "Web worker successfully created");
+
+  worker.onmessage = function(evt) {
+    var msg = evt.data || {};
+    if (msg.type == "test") {
+      ok(msg.result, msg.name);
+    }
+    if (msg.type == "finish") {
+      worker.terminate();
+      SimpleTest.finish();
+    }
+  }
+
+  ok(htmlCanvas.transferControlToOffscreen, "HTMLCanvasElement has transferControlToOffscreen function");
+
+  var offscreenCanvas = htmlCanvas.transferControlToOffscreen();
+  ok(offscreenCanvas, "Expected transferControlToOffscreen to succeed");
+
+  worker.postMessage({test: 'webgl', canvas: offscreenCanvas}, [offscreenCanvas]);
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_many.html b/dom/canvas/test/test_offscreencanvas_many.html
new file mode 100644
index 00000000000..6bf2680c50b
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_many.html
@@ -0,0 +1,67 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<!--
+  This test needs several workers run offscreen canvas simultaneously.
+  So we choose 8 workers, 4 of them run basic webgl drawing test and
+  others run size changing test.
+-->
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function createCanvas() {
+  var htmlCanvas = document.createElement('canvas');
+  htmlCanvas.width = 64;
+  htmlCanvas.height = 64;
+  document.body.appendChild(htmlCanvas);
+  return htmlCanvas;
+}
+
+function runTest() {
+  var stillRunning = 0;
+
+  var startWorker = function(canvas, test) {
+    stillRunning++;
+    var worker = new Worker("offscreencanvas.js");
+
+    worker.onmessage = function(evt) {
+      var msg = evt.data || {};
+      if (msg.type == "test") {
+        ok(msg.result, msg.name);
+      }
+      if (msg.type == "finish") {
+        worker.terminate();
+        if (--stillRunning == 0)
+          SimpleTest.finish();
+      }
+    }
+
+    var offscreenCanvas = canvas.transferControlToOffscreen();
+    worker.postMessage({test: test, canvas: offscreenCanvas}, [offscreenCanvas]);
+  }
+
+  /* create 4 workers that do the regular drawing test and 4 workers
+     that do the size change test */
+  for (var i = 0; i < 4; i++) {
+    startWorker(createCanvas(), 'webgl');
+  }
+
+  for (var i = 0; i < 4; i++) {
+    startWorker(createCanvas(), 'webgl_changesize');
+  }
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true]
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_neuter.html b/dom/canvas/test/test_offscreencanvas_neuter.html
new file mode 100644
index 00000000000..2af080c7c1e
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_neuter.html
@@ -0,0 +1,78 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>OffscreenCanvas: Test neutering</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<canvas id="c" width="64" height="64"></canvas>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+
+  var htmlCanvas = document.getElementById("c");
+  var worker = new Worker("offscreencanvas_neuter.js");
+
+  ok(htmlCanvas, "Should have HTML canvas element");
+  ok(worker, "Web worker successfully created");
+
+  ok(htmlCanvas.transferControlToOffscreen, "HTMLCanvasElement has transferControlToOffscreen function");
+
+  var offscreenCanvas = htmlCanvas.transferControlToOffscreen();
+  ok(offscreenCanvas, "Expected transferControlToOffscreen to succeed");
+
+  /* check html canvas is neuterd */
+  is(htmlCanvas.width, 64, "HTML canvas has correct width");
+  SimpleTest.doesThrow(
+    function() { htmlCanvas.width = 128; },
+    "Can't change html canvas' width after transferControlToOffscreen");
+
+  SimpleTest.doesThrow(
+    function() { htmlCanvas.height = 128; },
+    "Can't change html canvas' height after transferControlToOffscreen");
+
+  ok(!htmlCanvas.getContext("2d"), "Can't getContext after transferControlToOffscreen");
+  ok(!htmlCanvas.getContext("webgl"), "Can't getContext after transferControlToOffscreen");
+  ok(!htmlCanvas.getContext("webgl2"), "Can't getContext after transferControlToOffscreen");
+
+  worker.postMessage(offscreenCanvas, [offscreenCanvas]);
+
+  /* check parent offscreencanvas is neutered after being transfered */
+  SimpleTest.doesThrow(
+    function() { offscreenCanvas.width = 128; },
+    "Can't change transfered worker canvas width");
+
+  SimpleTest.doesThrow(
+    function() { offscreenCanvas.height = 128; },
+    "Can't change transfered worker canvas height");
+
+  SimpleTest.doesThrow(
+    function() { offscreenCanvas.getContext("2d") },
+    "Can't getContext on transfered worker canvas");
+
+  SimpleTest.doesThrow(
+    function() { offscreenCanvas.getContext("webgl") },
+    "Can't getContext on transfered worker canvas");
+
+  SimpleTest.doesThrow(
+    function() { offscreenCanvas.getContext("webgl2") },
+    "Can't getContext on transfered worker canvas");
+
+  // Transfer a neutered offscreencanvas should be ok.
+  worker.postMessage(offscreenCanvas, [offscreenCanvas]);
+
+  worker.terminate();
+  SimpleTest.finish();
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_serviceworker.html b/dom/canvas/test/test_offscreencanvas_serviceworker.html
new file mode 100644
index 00000000000..c5cfb93db1a
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_serviceworker.html
@@ -0,0 +1,46 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  window.onmessage = function(evt) {
+    var msg = evt.data || {};
+    if (msg.type == "test") {
+      ok(msg.result, msg.name);
+    }
+    if (msg.type == "finish") {
+      SimpleTest.finish();
+    }
+  }
+
+  navigator.serviceWorker.register('offscreencanvas.js', { scope: "."})
+    // Wait until the service worker is active.
+    .then(navigator.serviceWorker.ready)
+    // ...and then show the interface for the commands once it's ready.
+    .then(function() {
+      iframe = document.createElement("iframe");
+      iframe.setAttribute('src', "offscreencanvas_serviceworker_inner.html");
+      document.body.appendChild(iframe);
+    })
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+  ["dom.serviceWorkers.exemptFromPerDomainMax", true],
+  ["dom.serviceWorkers.interception.enabled", true],
+  ["dom.serviceWorkers.enabled", true],
+  ["dom.serviceWorkers.testing.enabled", true]
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_sharedworker.html b/dom/canvas/test/test_offscreencanvas_sharedworker.html
new file mode 100644
index 00000000000..28d7ce37c8a
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_sharedworker.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<canvas id="c" width="64" height="64"></canvas>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+
+  var htmlCanvas = document.getElementById("c");
+  var worker = new SharedWorker("offscreencanvas.js");
+
+  ok(htmlCanvas, "Should have HTML canvas element");
+  ok(worker, "Web worker successfully created");
+
+  ok(htmlCanvas.transferControlToOffscreen, "HTMLCanvasElement has transferControlToOffscreen function");
+
+  var offscreenCanvas = htmlCanvas.transferControlToOffscreen();
+  ok(offscreenCanvas, "Expected transferControlToOffscreen to succeed");
+
+  worker.port.start();
+
+  // We don't support transferring OffscreenCanvas via shared worker.
+  SimpleTest.doesThrow(
+    function() {
+      worker.port.postMessage({test: 'webgl', canvas: offscreenCanvas}, [offscreenCanvas]);
+    },
+    "OffscreenCanvas cannot transfer to shared worker"
+  );
+
+  SimpleTest.finish();
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_sizechange.html b/dom/canvas/test/test_offscreencanvas_sizechange.html
new file mode 100644
index 00000000000..cecbac34834
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_sizechange.html
@@ -0,0 +1,41 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>WebGL in OffscreenCanvas</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<canvas id="c" width="64" height="64"></canvas>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+
+  var htmlCanvas = document.getElementById("c");
+  var worker = new Worker("offscreencanvas.js");
+
+  worker.onmessage = function(evt) {
+    var msg = evt.data || {};
+    if (msg.type == "test") {
+      ok(msg.result, msg.name);
+    }
+    if (msg.type == "finish") {
+      worker.terminate();
+      SimpleTest.finish();
+    }
+  }
+
+  var offscreenCanvas = htmlCanvas.transferControlToOffscreen();
+  worker.postMessage({test: 'webgl_changesize', canvas: offscreenCanvas}, [offscreenCanvas]);
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/canvas/test/test_offscreencanvas_subworker.html b/dom/canvas/test/test_offscreencanvas_subworker.html
new file mode 100644
index 00000000000..b3fbae821c9
--- /dev/null
+++ b/dom/canvas/test/test_offscreencanvas_subworker.html
@@ -0,0 +1,90 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>OffscreenCanvas: Test subworkers</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+<!--
+  We want to test offscreen canvas works well when it running on worker
+  and nested worker simultaneously. So we create 10 canvas and dispatch
+  it to different workers and sub-workers.
+-->
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function createCanvas() {
+  var htmlCanvas = document.createElement('canvas');
+  htmlCanvas.width = 64;
+  htmlCanvas.height = 64;
+  document.body.appendChild(htmlCanvas);
+  return htmlCanvas.transferControlToOffscreen();
+}
+
+function runTest() {
+
+  var worker = new Worker("offscreencanvas.js");
+
+  worker.onmessage = function(evt) {
+    var msg = evt.data || {};
+    if (msg.type == "test") {
+      ok(msg.result, msg.name);
+    }
+    if (msg.type == "finish") {
+      worker.terminate();
+      SimpleTest.finish();
+    }
+  }
+
+  var findTransferables = function(t) {
+    if (t.test == "subworker") {
+      var result = [];
+      t.subtests.forEach(function(test) {
+        result = result.concat(findTransferables(test));
+      });
+
+      return result;
+    } else {
+      return [t.canvas];
+    }
+  };
+
+  var testData =
+    {test: 'subworker', subtests: [
+      {test: 'webgl', canvas: createCanvas()},
+      {test: 'subworker', subtests: [
+        {test: 'webgl', canvas: createCanvas()},
+        {test: 'webgl_changesize', canvas: createCanvas()},
+        {test: 'webgl', canvas: createCanvas()}
+      ]},
+      {test: 'subworker', subtests: [
+        {test: 'webgl', canvas: createCanvas()},
+        {test: 'webgl_changesize', canvas: createCanvas()},
+        {test: 'subworker', subtests: [
+          {test: 'webgl_changesize', canvas: createCanvas()},
+          {test: 'webgl', canvas: createCanvas()}
+        ]},
+        {test: 'subworker', subtests: [
+          {test: 'webgl_changesize', canvas: createCanvas()},
+          {test: 'subworker', subtests: [
+            {test: 'subworker', subtests: [
+              {test: 'webgl_changesize', canvas: createCanvas()}
+            ]}
+          ]}
+        ]},
+      ]}
+    ]};
+
+  worker.postMessage(testData, findTransferables(testData));
+}
+
+SpecialPowers.pushPrefEnv({'set': [
+  ['gfx.offscreencanvas.enabled', true],
+  ['webgl.force-enabled', true],
+]}, runTest);
+
+</script>
+</body>
+</html>