Bug 52509 – Shadow is not shown when using strokeRect with a gradient strokeStyle

• Component: Canvas
• Status: RESOLVED FIXED

[Helder Correia]

This happens in CG and is related to bug 51869, this time to be fixed in GraphicsContext::strokeRect(const FloatRect& r, float lineWidth). We need to draw the gradient clipped to the stroke on a CGLayer first, and then draw the layer on the GraphicsContext.

[Helder Correia]

Created attachment 79059 [details]
Patch

[Simon Fraser (smfr)]

Comment on attachment 79059 [details]
Patch

Why does this code do anything with m_state.fillGradient->gradientSpaceTransform() ?

[Helder Correia]

Created attachment 79887 [details]
Concat CTM with strokeGradient->gradientSpaceTransform()

[Helder Correia]

Created attachment 80979 [details]
Added svg/css/text-gradient-stroke-shadow.svg

[Build Bot]

Attachment 80979 [details] did not build on win:
Build output: http://queues.webkit.org/results/7690217

[Simon Fraser (smfr)]

Comment on attachment 80979 [details]
Added svg/css/text-gradient-stroke-shadow.svg

View in context: https://bugs.webkit.org/attachment.cgi?id=80979&action=review

> LayoutTests/svg/css/text-gradient-stroke-shadow.svg:8
> +<text x="100" y="300" style="font-size: 300px; text-shadow: #000 20px 20px 20px;" stroke-width="10" stroke="url(#gradient)">SVG</text>

Maybe just use a rect in these tests to avoid font differences between platforms.

Why does Mac render hollow characters, but the other platforms render solid black ones?

> Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp:972
> +            const float halfLineWidth = lineWidth / 2;

Can you add a comment explaining the lineWidth/2 offset? Why do it here, and not in the non-shadow path?

> Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp:1000
>  
> +

New blank line here.

[Helder Correia]

Created attachment 81121 [details]
New rect-gradient-stroke-shadow.svg. Add comment for line width. Fix build.

[Simon Fraser (smfr)]

Comment on attachment 81121 [details]
New rect-gradient-stroke-shadow.svg. Add comment for line width. Fix build.

View in context: https://bugs.webkit.org/attachment.cgi?id=81121&action=review

> Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp:988
> +            // Compensate for half of the line width, otherwise the layer's top-left corner would
> +            // be aligned with the rect's top-left corner, not considering the line width. This
> +            // would result in leaving half of the line out of the layer on the left and top sides.
> +            const float translationX = halfLineWidth - rect.x();
> +            const float translationY = halfLineWidth - rect.y();
> +            CGContextTranslateCTM(layerContext, translationX, translationY);
> +
> +            CGContextAddRect(layerContext, rect);
> +            CGContextReplacePathWithStrokedPath(layerContext);
> +            CGContextClip(layerContext);
> +            CGContextConcatCTM(layerContext, m_state.strokeGradient->gradientSpaceTransform());
> +            m_state.strokeGradient->paint(layerContext);
> +
> +            const float destinationX = rect.x() - halfLineWidth;
> +            const float destinationY = rect.y() - halfLineWidth;
> +            CGContextDrawLayerAtPoint(context, CGPointMake(destinationX, destinationY), layer);

I think you want to avoid drawing the layer at half-pixel offsets. Why not just round out the layer size to a whole pixel?

[Helder Correia]

Created attachment 81165 [details]
Ceil layer size and round blit destination.

[Tor Arne Vestbø]

Comment on attachment 81165 [details]
Ceil layer size and round blit destination.

View in context: https://bugs.webkit.org/attachment.cgi?id=81165&action=review

> Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp:193
> -    
> +

Please leave out these formatting hunks

[Helder Correia]

Created attachment 83698 [details]
Performance test

[Helder Correia]

Created attachment 83703 [details]
Remove formatting hunks

[Helder Correia]

Created attachment 83912 [details]
Otherwise the layer size will not be suficient to contain all pixels because of smoothing when we're scaling.

[Helder Correia]

Manually committed r80515: http://trac.webkit.org/changeset/80515

[Stephen Chenney]

Committed r114023: <http://trac.webkit.org/changeset/114023>