Use srcset's resource pixel density to determine intrinsic size

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 4bc56b201c406dea598180b30114f4f276b1512c..0f08c405b0f65b286602acd1660a22b5e37f440d 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -1207,11 +1207,22 @@ bool CanvasRenderingContext2D::shouldDrawShadows() const
     return alphaChannel(state().m_shadowColor) && (state().m_shadowBlur || !state().m_shadowOffset.isZero());
 }
 
-static LayoutSize sizeFor(HTMLImageElement* image)
+enum ImageSizeType {
+    ScaledSize,
+    UnscaledSize
+};
+
+static LayoutSize sizeFor(HTMLImageElement* image, ImageSizeType sizeType)

[pdr., 2013/10/11 05:17:33]

Can you help me understand why this is needed?

I thought canvas could only access the image size without the scale factor.
For example:
<img srcset="100x100.png 2x">

ctx.drawImage(img, 0, 0) should render at 50x50
and
ctx.drawImage(img, 0, 0, 100, 100) should render the original image (without
upscaling) at 100x100
and
ctx.drawImage(img, 0, 0, 1000, 1000) should render the original image upscaled
to 1000x1000

[Yoav Weiss, 2013/10/11 07:22:32]

For what I've seen, drawImage calls sizeFor 3 times:
* In CanvasRenderingContext2D:1376 it is called to determine the destination
canvas size. That size should be scaled (so 50x50 as you said for
ctx.drawImage(img, 0, 0))
* In CanvasRenderingContext2D:1387 it is called to determine the source image
size. Giving it scaled dimensions here resorts in only a quarter of the image
drawn.
* In CanvasRenderingContext2D:1418 it is called to determine the image
dimensions for clipping purposes. Giving scaled image dimensions here results in
image distortion.

 {
-    if (ImageResource* cachedImage = image->cachedImage())
-        return cachedImage->imageSizeForRenderer(image->renderer(), 1.0f); // FIXME: Not sure about this.
-    return IntSize();
+    LayoutSize size;
+    ImageResource* cachedImage = image->cachedImage();
+    if (cachedImage) {
+        size = cachedImage->imageSizeForRenderer(image->renderer(), 1.0f); // FIXME: Not sure about this.
+
+        if (sizeType == ScaledSize && image->renderer() && cachedImage->image() && !cachedImage->image()->hasRelativeWidth())
+            size.scale(image->renderer()->intrinsicSizeFactor());
+    }
+    return size;
 }
 
 static IntSize sizeFor(HTMLVideoElement* video)
@@ -1362,7 +1373,7 @@ void CanvasRenderingContext2D::drawImage(HTMLImageElement* image, float x, float
         es.throwUninformativeAndGenericDOMException(TypeMismatchError);
         return;
     }
-    LayoutSize size = sizeFor(image);
+    LayoutSize size = sizeFor(image, ScaledSize);
     drawImage(image, x, y, size.width(), size.height(), es);
 }
 
@@ -1373,7 +1384,7 @@ void CanvasRenderingContext2D::drawImage(HTMLImageElement* image,
         es.throwUninformativeAndGenericDOMException(TypeMismatchError);
         return;
     }
-    LayoutSize size = sizeFor(image);
+    LayoutSize size = sizeFor(image, UnscaledSize);
     drawImage(image, FloatRect(0, 0, size.width(), size.height()), FloatRect(x, y, width, height), es);
 }
 
@@ -1404,7 +1415,7 @@ void CanvasRenderingContext2D::drawImage(HTMLImageElement* image, const FloatRec
     if (!cachedImage || !image->complete())
         return;
 
-    LayoutSize size = sizeFor(image);
+    LayoutSize size = sizeFor(image, UnscaledSize);
     if (!size.width() || !size.height()) {
         es.throwUninformativeAndGenericDOMException(InvalidStateError);
         return;