Allow ImageBitmaps derived from HTMLImageElements to be evicted from RAM.

Source/core/page/ImageBitmap.cpp

 // Copyright 2013 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 "config.h"
 #include "core/page/ImageBitmap.h"
 
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLVideoElement.h"
@@ skipping 20 matching lines @@
     image->nativeImageForCurrentFrame()->bitmap().extractSubset(&cropped, cropRect);
     return BitmapImage::create(NativeImageSkia::create(cropped));
 }
 
 ImageBitmap::ImageBitmap(HTMLImageElement* image, const IntRect& cropRect)
     : m_cropRect(cropRect)
     , m_imageElement(image)
 {
     m_imageElement->addClient(this);
 
-    IntSize bitmapSize = intersection(cropRect, IntRect(0, 0, image->width(), image->height())).size();
-    m_bitmapRect = IntRect(IntPoint(max(0, -cropRect.x()), max(0, -cropRect.y())), bitmapSize);
+    IntRect srcRect = intersection(cropRect, IntRect(0, 0, image->width(), image->height()));
+    m_bitmapRect = IntRect(IntPoint(max(0, -cropRect.x()), max(0, -cropRect.y())), srcRect.size());
+    m_bitmapOffset = srcRect.location();
 
     ScriptWrappable::init(this);
 }
 
 ImageBitmap::ImageBitmap(HTMLVideoElement* video, const IntRect& cropRect)
     : m_cropRect(cropRect)
     , m_imageElement(0)
+    , m_bitmapOffset(IntPoint())

[Stephen White, 2013/08/08 15:32:11]

Out of curiosity, why don't we set a bitmap offset in the video and
canvas-to-canvas cases?

 {
     IntRect videoRect = IntRect(IntPoint(), video->player()->naturalSize());
     IntRect srcRect = intersection(cropRect, videoRect);
     IntRect dstRect(IntPoint(), srcRect.size());
 
     m_buffer = ImageBuffer::create(videoRect.size());
     GraphicsContext* c = m_buffer->context();
     c->clip(dstRect);
     c->translate(-srcRect.x(), -srcRect.y());
     video->paintCurrentFrameInContext(c, videoRect);
     m_bitmap = m_buffer->copyImage(DontCopyBackingStore);
     m_bitmapRect = IntRect(IntPoint(max(0, -cropRect.x()), max(0, -cropRect.y())), srcRect.size());
 
     ScriptWrappable::init(this);
 }
 
 ImageBitmap::ImageBitmap(HTMLCanvasElement* canvas, const IntRect& cropRect)
     : m_cropRect(cropRect)
     , m_imageElement(0)
+    , m_bitmapOffset(IntPoint())
 {
     IntSize canvasSize = canvas->size();
     IntRect srcRect = intersection(cropRect, IntRect(IntPoint(), canvasSize));
     IntRect dstRect(IntPoint(), srcRect.size());
 
     m_buffer = ImageBuffer::create(canvasSize);
     m_buffer->context()->drawImageBuffer(canvas->buffer(), dstRect, srcRect);
     m_bitmap = m_buffer->copyImage(DontCopyBackingStore);
     m_bitmapRect = IntRect(IntPoint(max(0, -cropRect.x()), max(0, -cropRect.y())), srcRect.size());
 
     ScriptWrappable::init(this);
 }
 
 ImageBitmap::ImageBitmap(ImageData* data, const IntRect& cropRect)
     : m_cropRect(cropRect)
     , m_imageElement(0)
+    , m_bitmapOffset(IntPoint())
 {
     IntRect srcRect = intersection(cropRect, IntRect(IntPoint(), data->size()));
 
     m_buffer = ImageBuffer::create(data->size());
     if (srcRect.width() > 0 && srcRect.height() > 0)
         m_buffer->putByteArray(Unmultiplied, data->data(), data->size(), srcRect, IntPoint(min(0, -cropRect.x()), min(0, -cropRect.y())));
 
     m_bitmap = m_buffer->copyImage(DontCopyBackingStore);
     m_bitmapRect = IntRect(IntPoint(max(0, -cropRect.x()), max(0, -cropRect.y())),  srcRect.size());
 
     ScriptWrappable::init(this);
 }
 
 ImageBitmap::ImageBitmap(ImageBitmap* bitmap, const IntRect& cropRect)
     : m_cropRect(cropRect)
     , m_imageElement(bitmap->imageElement())

[Stephen White, 2013/08/08 15:32:11]

Nit: might be clearer to initialize m_bitmapOffset to IntPoint(), then only
assign it in the first case below.

 {
     IntRect oldBitmapRect = bitmap->bitmapRect();
-    IntSize bitmapSize = intersection(cropRect, oldBitmapRect).size();
-    IntPoint bitmapOffset(max(0, oldBitmapRect.x() - cropRect.x()), max(0, oldBitmapRect.y() - cropRect.y()));
-    m_bitmapRect = IntRect(bitmapOffset, bitmapSize);
+    IntRect srcRect = intersection(cropRect, oldBitmapRect);
+    m_bitmapRect = IntRect(IntPoint(max(0, oldBitmapRect.x() - cropRect.x()), max(0, oldBitmapRect.y() - cropRect.y())), srcRect.size());
+
     if (m_imageElement) {
         m_imageElement->addClient(this);
         m_bitmap = 0;
+        m_bitmapOffset = srcRect.location();
     } else {
         IntRect adjustedCropRect(IntPoint(cropRect.x() -oldBitmapRect.x(), cropRect.y() - oldBitmapRect.y()), cropRect.size());
         m_bitmap = cropImage(bitmap->bitmapImage().get(), adjustedCropRect);
+        m_bitmapOffset = IntPoint();
     }
     ScriptWrappable::init(this);
 }
 
 ImageBitmap::~ImageBitmap()
 {
     if (m_imageElement)
         m_imageElement->removeClient(this);
 }
 
@@ skipping 28 matching lines @@
 PassRefPtr<ImageBitmap> ImageBitmap::create(ImageBitmap* bitmap, const IntRect& cropRect)
 {
     IntRect normalizedCropRect = normalizeRect(cropRect);
     RefPtr<ImageBitmap> imageBitmap(adoptRef(new ImageBitmap(bitmap, normalizedCropRect)));
     return imageBitmap.release();
 }
 
 void ImageBitmap::notifyImageSourceChanged()
 {
     m_bitmap = cropImage(m_imageElement->cachedImage()->image(), m_cropRect);
+    m_bitmapOffset = IntPoint();
     m_imageElement = 0;
 }
 
 PassRefPtr<Image> ImageBitmap::bitmapImage() const
 {
     ASSERT((m_imageElement || m_bitmap) && (!m_imageElement || !m_bitmap));
     if (m_imageElement)
-        return cropImage(m_imageElement->cachedImage()->image(), m_cropRect);
+        return m_imageElement->cachedImage()->image();
     return m_bitmap;
 }
 
 }