Add ImageBitmapRenderingContext (experimental)

third_party/WebKit/Source/modules/imagebitmap/ImageBitmapRenderingContext.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "modules/imagebitmap/ImageBitmapRenderingContext.h"
+
+#include "core/frame/ImageBitmap.h"
+#include "platform/graphics/GraphicsContext.h"
+#include "platform/graphics/StaticBitmapImage.h"
+#include "third_party/skia/include/core/SkImage.h"
+#include "third_party/skia/include/core/SkSurface.h"
+
+namespace blink {
+
+ImageBitmapRenderingContext::ImageBitmapRenderingContext(HTMLCanvasElement* canvas, CanvasContextCreationAttributes attrs, Document& document)
+    : CanvasRenderingContext(canvas)
+    , m_hasAlpha(attrs.alpha())
+{ }
+
+ImageBitmapRenderingContext::~ImageBitmapRenderingContext() { }
+
+void ImageBitmapRenderingContext::transferImageBitmap(ImageBitmap* imageBitmap)
+{
+    m_image = imageBitmap->bitmapImage();

[Stephen White, 2016/02/10 15:34:55]

colorPicker->pickColorColorPickPick().  :)

[Justin Novosad, 2016/02/10 15:50:21]

LOL!!!  The old days...

+    if (!m_image)
+        return;
+
+    RefPtr<SkImage> skImage = m_image->imageForCurrentFrame();
+    if (skImage->isTextureBacked()) {
+        // TODO(junov): crbug.com/585607 Eliminate this readback and use an ExternalTextureLayer

[Stephen White, 2016/02/10 15:34:55]

Should we do this check only for display-list canvas, if possible?

[Justin Novosad, 2016/02/10 15:50:21]

It is not display list canvas that is the problem, It's blink display lists
(impl-side rasterization).

[Stephen White, 2016/02/10 15:56:08]

Right, but isn't impl-side rasterization only utilized in display list mode?
Otherwise we do raster in the renderer
process, no? I was thinking that if there was a way to detect it, we could do
GPU raster without a readback (and 
without an external texture layer) when in non-display-list mode. Then again,
I'm not certain I understand if/how 
this new context interacts with the different canvas rendering modes.

Doesn't have to be in this patch, just some food for thought.

[Justin Novosad, 2016/02/10 16:09:29]

There is no "display list mode". The concept of display list mode only exist in
2D canvases. This is an imagebitmap canvas. All this context does is dump a
bitmap into the containing layer's GraphicsContext. The GraphicsContext records
into a blink DisplayListItem that gets rasterized by the compositor. This flow
does not support GPU-backed bitmaps, ever. The only way to prevent the readback
is to set up an "ImageBitmapLayerBridge", which is what crbug.com/585607 is
about.

[Stephen White, 2016/02/10 16:11:34]

Acknowledged. These are not the nits you're looking for. You may go about your
business.

+        RefPtr<SkSurface> surface = SkSurface::NewRasterN32Premul(skImage->width(), skImage->height());
+        if (!surface) {
+            // silent failure

[Stephen White, 2016/02/10 15:34:55]

Is a silent failure spec-compliant? If not, please file a bug.

[Justin Novosad, 2016/02/10 15:50:21]

The handling of general OOM failures is not specified AFAIK
It is either this or crash (or draw a sad canvas?).  The pre-existing policy in
2D canvas is to let the canvas be blank if we fail to allocate it's backing
store. This is the ImageBitmap equivalent of the same behavior.

[Stephen White, 2016/02/10 15:56:08]

Acknowledged.

+            m_image.clear();
+            return;
+        }
+        surface->getCanvas()->drawImage(skImage.get(), 0, 0);
+        m_image = StaticBitmapImage::create(surface->newImageSnapshot());
+    }
+    canvas()->didDraw(FloatRect(FloatPoint(), FloatSize(m_image->width(), m_image->height())));
+}
+
+bool ImageBitmapRenderingContext::paint(GraphicsContext& gc, const IntRect& r)
+{
+    if (!m_image)
+        return true;
+
+    // With impl-side painting, it is unsafe to use a gpu-backed SkImage
+    ASSERT(!m_image->imageForCurrentFrame()->isTextureBacked());
+    gc.drawImage(m_image.get(), r, m_hasAlpha ? SkXfermode::kSrcOver_Mode : SkXfermode::kSrc_Mode);
+
+    return true;
+}
+
+PassOwnPtrWillBeRawPtr<CanvasRenderingContext> ImageBitmapRenderingContext::Factory::create(HTMLCanvasElement* canvas, const CanvasContextCreationAttributes& attrs, Document& document)
+{
+    if (!RuntimeEnabledFeatures::experimentalCanvasFeaturesEnabled())
+        return nullptr;
+    return adoptPtrWillBeNoop(new ImageBitmapRenderingContext(canvas, attrs, document));
+}
+
+void ImageBitmapRenderingContext::stop()
+{
+    m_image.clear();
+}
+
+} // blink