Bug 1746750 - Part 3. Implement partial OffscreenCanvasRenderingContext2D. r=lsalzman,webidl,smaug

This patch adds a partial OffscreenCanvasRenderingContext2D
implementation. It is missing anything text and UI related, including
CanvasFilters, CanvasUserInterface, CanvasText, CanvasTextDrawingStyles,
and CanvasHitRegions.

Differential Revision: https://phabricator.services.mozilla.com/D135354

dom/bindings/Bindings.conf

@@ -609,6 +609,12 @@ DOMInterfaces = {
     'nativeType': 'nsDOMOfflineResourceList',
 },
 
+'OffscreenCanvasRenderingContext2D': {
+    'implicitJSContext': [
+        'createImageData', 'getImageData', 'isPointInPath', 'isPointInStroke'
+    ],
+},
+
 'PaintRequestList': {
     'headerFile': 'mozilla/dom/PaintRequest.h',
 },

dom/canvas/CanvasRenderingContext2D.cpp

@@ -1140,15 +1140,15 @@ nsresult CanvasRenderingContext2D::Redraw() {
 
   mIsEntireFrameInvalid = true;
 
-  if (!mCanvasElement) {
+  if (mCanvasElement) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
+    mCanvasElement->InvalidateCanvasContent(nullptr);
+  } else if (mOffscreenCanvas) {
+    mOffscreenCanvas->QueueCommitToCompositor();
+  } else {
     NS_ASSERTION(mDocShell, "Redraw with no canvas element or docshell!");
-    return NS_OK;
   }
 
-  SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
-
-  mCanvasElement->InvalidateCanvasContent(nullptr);
-
   return NS_OK;
 }
 
@@ -1166,14 +1166,14 @@ void CanvasRenderingContext2D::Redraw(const gfx::Rect& aR) {
     return;
   }
 
-  if (!mCanvasElement) {
+  if (mCanvasElement) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
+    mCanvasElement->InvalidateCanvasContent(&aR);
+  } else if (mOffscreenCanvas) {
+    mOffscreenCanvas->QueueCommitToCompositor();
+  } else {
     NS_ASSERTION(mDocShell, "Redraw with no canvas element or docshell!");
-    return;
   }
-
-  SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
-
-  mCanvasElement->InvalidateCanvasContent(&aR);
 }
 
 void CanvasRenderingContext2D::DidRefresh() {}
@@ -1563,6 +1563,14 @@ void CanvasRenderingContext2D::ClearTarget(int32_t aWidth, int32_t aHeight) {
     }
   }
 
+  if (mOffscreenCanvas) {
+    OffscreenCanvasDisplayData data;
+    data.mSize = {mWidth, mHeight};
+    data.mIsOpaque = mOpaque;
+    data.mIsAlphaPremult = true;
+    mOffscreenCanvas->UpdateDisplayData(data);
+  }
+
   if (!mCanvasElement || !mCanvasElement->IsInComposedDoc()) {
     return;
   }

dom/canvas/CanvasRenderingContextHelper.cpp

@@ -9,6 +9,7 @@
 #include "ImageEncoder.h"
 #include "mozilla/dom/BlobImpl.h"
 #include "mozilla/dom/CanvasRenderingContext2D.h"
+#include "mozilla/dom/OffscreenCanvasRenderingContext2D.h"
 #include "mozilla/GfxMessageUtils.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/UniquePtr.h"
@@ -137,6 +138,11 @@ CanvasRenderingContextHelper::CreateContextHelper(
       ret = new CanvasRenderingContext2D(aCompositorBackend);
       break;
 
+    case CanvasContextType::OffscreenCanvas2D:
+      Telemetry::Accumulate(Telemetry::CANVAS_2D_USED, 1);
+      ret = new OffscreenCanvasRenderingContext2D(aCompositorBackend);
+      break;
+
     case CanvasContextType::WebGL1:
       Telemetry::Accumulate(Telemetry::CANVAS_WEBGL_USED, 1);
 

dom/canvas/CanvasRenderingContextHelper.h

@@ -25,6 +25,7 @@ class EncodeCompleteCallback;
 enum class CanvasContextType : uint8_t {
   NoContext,
   Canvas2D,
+  OffscreenCanvas2D,
   WebGL1,
   WebGL2,
   WebGPU,

dom/canvas/OffscreenCanvas.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/dom/BlobImpl.h"
 #include "mozilla/dom/OffscreenCanvasBinding.h"
 #include "mozilla/dom/OffscreenCanvasDisplayHelper.h"
+#include "mozilla/dom/OffscreenCanvasRenderingContext2D.h"
 #include "mozilla/dom/Promise.h"
 #include "mozilla/dom/WorkerPrivate.h"
 #include "mozilla/dom/WorkerScope.h"
@@ -118,6 +119,9 @@ void OffscreenCanvas::GetContext(
 
   CanvasContextType contextType;
   switch (aContextId) {
+    case OffscreenRenderingContextId::_2d:
+      contextType = CanvasContextType::OffscreenCanvas2D;
+      break;
     case OffscreenRenderingContextId::Bitmaprenderer:
       contextType = CanvasContextType::ImageBitmap;
       break;
@@ -148,6 +152,11 @@ void OffscreenCanvas::GetContext(
 
   MOZ_ASSERT(mCurrentContext);
   switch (mCurrentContextType) {
+    case CanvasContextType::OffscreenCanvas2D:
+      aResult.SetValue().SetAsOffscreenCanvasRenderingContext2D() =
+          *static_cast<OffscreenCanvasRenderingContext2D*>(
+              mCurrentContext.get());
+      break;
     case CanvasContextType::ImageBitmap:
       aResult.SetValue().SetAsImageBitmapRenderingContext() =
           *static_cast<ImageBitmapRenderingContext*>(mCurrentContext.get());
@@ -305,6 +314,12 @@ already_AddRefed<Promise> OffscreenCanvas::ConvertToBlob(
     return nullptr;
   }
 
+  if (mNeutered) {
+    aRv.ThrowInvalidStateError(
+        "Cannot get blob from placeholder canvas transferred to worker.");
+    return nullptr;
+  }
+
   nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
 
   RefPtr<Promise> promise = Promise::Create(global, aRv);
@@ -327,6 +342,9 @@ already_AddRefed<Promise> OffscreenCanvas::ConvertToBlob(
   CanvasRenderingContextHelper::ToBlob(callback, type, encodeOptions,
                                        /* aUsingCustomOptions */ false,
                                        usePlaceholder, aRv);
+  if (aRv.Failed()) {
+    promise->MaybeReject(std::move(aRv));
+  }
 
   return promise.forget();
 }
@@ -341,6 +359,12 @@ already_AddRefed<Promise> OffscreenCanvas::ToBlob(JSContext* aCx,
     return nullptr;
   }
 
+  if (mNeutered) {
+    aRv.ThrowInvalidStateError(
+        "Cannot get blob from placeholder canvas transferred to worker.");
+    return nullptr;
+  }
+
   nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
 
   RefPtr<Promise> promise = Promise::Create(global, aRv);

dom/canvas/OffscreenCanvas.h

@@ -36,7 +36,7 @@ class ImageBitmap;
 struct ImageEncodeOptions;
 
 using OwningOffscreenRenderingContext = class
-    OwningImageBitmapRenderingContextOrWebGLRenderingContextOrWebGL2RenderingContextOrGPUCanvasContext;
+    OwningOffscreenCanvasRenderingContext2DOrImageBitmapRenderingContextOrWebGLRenderingContextOrWebGL2RenderingContextOrGPUCanvasContext;
 
 // This is helper class for transferring OffscreenCanvas to worker thread.
 // Because OffscreenCanvas is not thread-safe. So we cannot pass Offscreen-
@@ -151,6 +151,8 @@ class OffscreenCanvas final : public DOMEventTargetHelper,
 
   bool ShouldResistFingerprinting() const;
 
+  bool IsTransferredFromElement() const { return !!mDisplay; }
+
  private:
   ~OffscreenCanvas();
 

dom/canvas/OffscreenCanvasRenderingContext2D.cpp

@@ -0,0 +1,117 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "OffscreenCanvasRenderingContext2D.h"
+#include "mozilla/dom/OffscreenCanvasRenderingContext2DBinding.h"
+#include "mozilla/dom/OffscreenCanvas.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerRef.h"
+
+namespace mozilla::dom {
+
+class OffscreenCanvasShutdownObserver final {
+  NS_INLINE_DECL_REFCOUNTING(OffscreenCanvasShutdownObserver)
+
+ public:
+  explicit OffscreenCanvasShutdownObserver(
+      OffscreenCanvasRenderingContext2D* aOwner)
+      : mOwner(aOwner) {}
+
+  void OnShutdown() {
+    if (mOwner) {
+      mOwner->OnShutdown();
+      mOwner = nullptr;
+    }
+  }
+
+  void ClearOwner() { mOwner = nullptr; }
+
+ private:
+  ~OffscreenCanvasShutdownObserver() = default;
+
+  OffscreenCanvasRenderingContext2D* mOwner;
+};
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_INHERITED(
+    OffscreenCanvasRenderingContext2D, CanvasRenderingContext2D)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(OffscreenCanvasRenderingContext2D)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+NS_INTERFACE_MAP_END_INHERITING(CanvasRenderingContext2D)
+
+NS_IMPL_ADDREF_INHERITED(OffscreenCanvasRenderingContext2D,
+                         CanvasRenderingContext2D)
+NS_IMPL_RELEASE_INHERITED(OffscreenCanvasRenderingContext2D,
+                          CanvasRenderingContext2D)
+
+OffscreenCanvasRenderingContext2D::OffscreenCanvasRenderingContext2D(
+    layers::LayersBackend aCompositorBackend)
+    : CanvasRenderingContext2D(aCompositorBackend) {}
+
+OffscreenCanvasRenderingContext2D::~OffscreenCanvasRenderingContext2D() =
+    default;
+
+JSObject* OffscreenCanvasRenderingContext2D::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return OffscreenCanvasRenderingContext2D_Binding::Wrap(aCx, this,
+                                                         aGivenProto);
+}
+
+nsIGlobalObject* OffscreenCanvasRenderingContext2D::GetParentObject() const {
+  return mOffscreenCanvas->GetOwnerGlobal();
+}
+
+void OffscreenCanvasRenderingContext2D::AddShutdownObserver() {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  if (!workerPrivate) {
+    // We may be using OffscreenCanvas on the main thread.
+    CanvasRenderingContext2D::AddShutdownObserver();
+    return;
+  }
+
+  mOffscreenShutdownObserver =
+      MakeAndAddRef<OffscreenCanvasShutdownObserver>(this);
+  mWorkerRef = WeakWorkerRef::Create(
+      workerPrivate,
+      [observer = mOffscreenShutdownObserver] { observer->OnShutdown(); });
+}
+
+void OffscreenCanvasRenderingContext2D::RemoveShutdownObserver() {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  if (!workerPrivate) {
+    // We may be using OffscreenCanvas on the main thread.
+    CanvasRenderingContext2D::RemoveShutdownObserver();
+    return;
+  }
+
+  if (mOffscreenShutdownObserver) {
+    mOffscreenShutdownObserver->ClearOwner();
+  }
+  mOffscreenShutdownObserver = nullptr;
+  mWorkerRef = nullptr;
+}
+
+void OffscreenCanvasRenderingContext2D::OnShutdown() {
+  if (mOffscreenShutdownObserver) {
+    mOffscreenShutdownObserver->ClearOwner();
+    mOffscreenShutdownObserver = nullptr;
+  }
+
+  CanvasRenderingContext2D::OnShutdown();
+}
+
+void OffscreenCanvasRenderingContext2D::Commit(ErrorResult& aRv) {
+  if (!mOffscreenCanvas->IsTransferredFromElement()) {
+    aRv.ThrowInvalidStateError(
+        "Cannot commit on an OffscreenCanvas that is not transferred from an "
+        "HTMLCanvasElement.");
+    return;
+  }
+
+  mOffscreenCanvas->CommitFrameToCompositor();
+}
+
+}  // namespace mozilla::dom

dom/canvas/OffscreenCanvasRenderingContext2D.h

@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_DOM_OFFSCREENCANVASRENDERINGCONTEXT2D_H_
+#define MOZILLA_DOM_OFFSCREENCANVASRENDERINGCONTEXT2D_H_
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/CanvasRenderingContext2D.h"
+
+struct JSContext;
+class nsIGlobalObject;
+
+namespace mozilla::dom {
+class OffscreenCanvas;
+class OffscreenCanvasShutdownObserver;
+class WeakWorkerRef;
+
+class OffscreenCanvasRenderingContext2D final
+    : public CanvasRenderingContext2D {
+ public:
+  // nsISupports interface + CC
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(
+      OffscreenCanvasRenderingContext2D, CanvasRenderingContext2D)
+
+  explicit OffscreenCanvasRenderingContext2D(
+      layers::LayersBackend aCompositorBackend);
+
+  nsIGlobalObject* GetParentObject() const;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  OffscreenCanvas* Canvas() { return mOffscreenCanvas; }
+  const OffscreenCanvas* Canvas() const { return mOffscreenCanvas; }
+
+  void Commit(ErrorResult& aRv);
+
+  void OnShutdown() override;
+
+ private:
+  void AddShutdownObserver() override;
+  void RemoveShutdownObserver() override;
+  bool AlreadyShutDown() const override {
+    return !mOffscreenShutdownObserver &&
+           CanvasRenderingContext2D::AlreadyShutDown();
+  }
+
+  ~OffscreenCanvasRenderingContext2D() override;
+
+  RefPtr<OffscreenCanvasShutdownObserver> mOffscreenShutdownObserver;
+  RefPtr<WeakWorkerRef> mWorkerRef;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // MOZILLA_DOM_OFFSCREENCANVASRENDERINGCONTEXT2D_H_

dom/canvas/moz.build

@@ -61,6 +61,7 @@ EXPORTS.mozilla.dom += [
     "ImageUtils.h",
     "OffscreenCanvas.h",
     "OffscreenCanvasDisplayHelper.h",
+    "OffscreenCanvasRenderingContext2D.h",
     "QueueParamTraits.h",
     "TextMetrics.h",
     "WebGLChild.h",
@@ -101,6 +102,7 @@ SOURCES += [
     "DrawTargetWebgl.cpp",  # Isolate Skia
     "ImageUtils.cpp",
     "OffscreenCanvasDisplayHelper.cpp",  # See bug 1745384
+    "OffscreenCanvasRenderingContext2D.cpp",  # See bug 1745384
 ]
 
 # WebGL Sources

dom/webidl/CanvasRenderingContext2D.webidl

@@ -338,7 +338,8 @@ interface mixin CanvasHitRegions {
   [Pref="canvas.hitregions.enabled"] void clearHitRegions();
 };
 
-[Exposed=Window]
+[Exposed=(Window,Worker),
+ Func="mozilla::dom::OffscreenCanvas::PrefEnabledOnWorkerThread"]
 interface CanvasGradient {
   // opaque object
   [Throws]
@@ -346,7 +347,8 @@ interface CanvasGradient {
   void addColorStop(float offset, UTF8String color);
 };
 
-[Exposed=Window]
+[Exposed=(Window,Worker),
+ Func="mozilla::dom::OffscreenCanvas::PrefEnabledOnWorkerThread"]
 interface CanvasPattern {
   // opaque object
   // [Throws, LenientFloat] - could not do this overload because of bug 1020975
@@ -397,7 +399,8 @@ interface TextMetrics {
 };
 
 [Pref="canvas.path.enabled",
- Exposed=Window]
+ Func="mozilla::dom::OffscreenCanvas::PrefEnabledOnWorkerThread",
+ Exposed=(Window,Worker)]
 interface Path2D
 {
   constructor();

dom/webidl/OffscreenCanvas.webidl

@@ -7,14 +7,14 @@
  * https://html.spec.whatwg.org/#the-offscreencanvas-interface
  */
 
-typedef (ImageBitmapRenderingContext or WebGLRenderingContext or WebGL2RenderingContext or GPUCanvasContext) OffscreenRenderingContext;
+typedef (OffscreenCanvasRenderingContext2D or ImageBitmapRenderingContext or WebGLRenderingContext or WebGL2RenderingContext or GPUCanvasContext) OffscreenRenderingContext;
 
 dictionary ImageEncodeOptions {
   DOMString type = "image/png";
   unrestricted double quality;
 };
 
-enum OffscreenRenderingContextId { /* "2d", */ "bitmaprenderer", "webgl", "webgl2", "webgpu" };
+enum OffscreenRenderingContextId { "2d", "bitmaprenderer", "webgl", "webgl2", "webgpu" };
 
 [Exposed=(Window,Worker),
  Func="CanvasUtils::IsOffscreenCanvasEnabled"]

dom/webidl/OffscreenCanvasRenderingContext2D.webidl

@@ -0,0 +1,30 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * For more information on this interface, please see
+ * https://html.spec.whatwg.org/#the-offscreen-2d-rendering-context
+ */
+
+[Exposed=(Window,Worker),
+ Func="CanvasUtils::IsOffscreenCanvasEnabled"]
+interface OffscreenCanvasRenderingContext2D {
+  [Throws]
+  void commit();
+
+  readonly attribute OffscreenCanvas canvas;
+};
+
+OffscreenCanvasRenderingContext2D includes CanvasState;
+OffscreenCanvasRenderingContext2D includes CanvasTransform;
+OffscreenCanvasRenderingContext2D includes CanvasCompositing;
+OffscreenCanvasRenderingContext2D includes CanvasImageSmoothing;
+OffscreenCanvasRenderingContext2D includes CanvasFillStrokeStyles;
+OffscreenCanvasRenderingContext2D includes CanvasShadowStyles;
+OffscreenCanvasRenderingContext2D includes CanvasRect;
+OffscreenCanvasRenderingContext2D includes CanvasDrawPath;
+OffscreenCanvasRenderingContext2D includes CanvasDrawImage;
+OffscreenCanvasRenderingContext2D includes CanvasImageData;
+OffscreenCanvasRenderingContext2D includes CanvasPathDrawingStyles;
+OffscreenCanvasRenderingContext2D includes CanvasPathMethods;

dom/webidl/moz.build

@@ -241,6 +241,9 @@ with Files("OfflineAudio*"):
 with Files("OffscreenCanvas.webidl"):
     BUG_COMPONENT = ("Core", "Canvas: 2D")
 
+with Files("OffscreenCanvasRenderingContext2D.webidl"):
+    BUG_COMPONENT = ("Core", "Canvas: 2D")
+
 with Files("OscillatorNode.webidl"):
     BUG_COMPONENT = ("Core", "Web Audio")
 
@@ -752,6 +755,7 @@ WEBIDL_FILES = [
     "OfflineAudioContext.webidl",
     "OfflineResourceList.webidl",
     "OffscreenCanvas.webidl",
+    "OffscreenCanvasRenderingContext2D.webidl",
     "OscillatorNode.webidl",
     "PaintRequest.webidl",
     "PaintRequestList.webidl",

modules/libpref/init/StaticPrefList.yaml

@@ -1525,7 +1525,7 @@
 
 # Add support for canvas path objects
 - name: canvas.path.enabled
-  type: bool
+  type: RelaxedAtomicBool
   value: true
   mirror: always