Fixing the Snapshot method in HTMLCanvasElement to work with BitmapRenderer

Resorting the code into snapshot method as to make easier to understand.
Now snapshot will effectively ask for a GetImage in case that the context
is ImageBitmapRenderer.

Adding some comments to html_canvas_element.h to explain the types of
contexts that can be into the html_canvas_element and adding future todo.

Adding test to validate that getDataURL works on the bitmaprenderer context.

Bug: 932266, 838108
Change-Id: I96aa25a3db624a2ddf457ae7349e345955e9ad50
Reviewed-on: https://chromium-review.googlesource.com/c/1481107Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Juanmi Huertas <juanmihd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635634}

third_party/blink/renderer/core/html/canvas/html_canvas_element.cc

@@ -795,8 +795,12 @@ scoped_refptr<StaticBitmapImage> HTMLCanvasElement::Snapshot(
     AccelerationHint hint) const {
   if (size_.IsEmpty())
     return nullptr;
+
   scoped_refptr<StaticBitmapImage> image_bitmap = nullptr;
-  if (Is3d()) {
+  if (PlaceholderFrame()) {  // Offscreen Canvas
+    DCHECK(PlaceholderFrame()->OriginClean());
+    image_bitmap = PlaceholderFrame()->Bitmap();
+  } else if (Is3d()) {  // WebGL or WebGL2 canvas
     if (context_->CreationAttributes().premultiplied_alpha) {
       context_->PaintRenderingResultsToCanvas(source_buffer);
       if (ResourceProvider())
@@ -818,15 +822,13 @@ scoped_refptr<StaticBitmapImage> HTMLCanvasElement::Snapshot(
         image_bitmap = StaticBitmapImage::Create(std::move(data_array), info);
       }
     }
-  } else if (context_ || PlaceholderFrame()) {
-    DCHECK(Is2d() || PlaceholderFrame());
-    if (canvas2d_bridge_) {
-      image_bitmap = canvas2d_bridge_->NewImageSnapshot(hint);
-    } else if (PlaceholderFrame()) {
-      DCHECK(PlaceholderFrame()->OriginClean());
-      image_bitmap = PlaceholderFrame()->Bitmap();
-    }
+  } else if (canvas2d_bridge_) {  // 2D Canvas
+    DCHECK(Is2d());
+    image_bitmap = canvas2d_bridge_->NewImageSnapshot(hint);
+  } else if (context_) {  // Bitmap renderer canvas
+    image_bitmap = context_->GetImage(hint);
   }
+
   if (!image_bitmap)
     image_bitmap = CreateTransparentImage(size_);
   return image_bitmap;

third_party/blink/renderer/core/html/canvas/html_canvas_element.h

@@ -86,6 +86,16 @@ typedef CanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContextO
     RenderingContext;
 #endif
 
+// This contains the information of HTML Canvas Element,
+// There are four different types of context this HTML Canvas can contain.
+// It can be a 3D Context (WebGL or WebGL2), 2D Context,
+// BitmapRenderingContext or it can have no context (Offscreencanvas).
+// To check the no context case is good to check if there is a placeholder.
+// For 3D and 2D contexts there are Is3D or Is2D functions.
+// The remaining case is BitmaprenderingContext.
+//
+// TODO (juanmihd): Study if a refactor of context could help in simplifying
+// this class and without overcomplicating context.
 class CORE_EXPORT HTMLCanvasElement final
     : public HTMLElement,
       public ContextLifecycleObserver,

third_party/blink/web_tests/fast/canvas/canvas-toDataURL-bitmaprenderer.html

+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+
+<script>
+
+function testGetURL(image) {
+	var can = document.createElement('canvas');
+	var ctx = can.getContext('bitmaprenderer');
+	ctx.transferFromImageBitmap(image);
+	var dataURL = can.toDataURL();
+
+	assert_equals(dataURL, image.src);
+}
+
+test(function(t) {
+	var magentaPixelImg = document.createElement('img');
+	// This is a base64 encoded string representing a single magenta pixel
+	magentaPixelImg.src = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z/D/PwAHAwL/qGeMxAAAAABJRU5ErkJggg==";
+	createImageBitmap(magentaPixelImg,0,0,magentaPixelImg.naturalWidth,magentaPixelImg.naturalHeight).then(testGetURL);
+}, "Test that canvas toDataURL returns the same URL that was expected when the canvas is of bitmaprenderer type.")
+
+</script>
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