[cairo][SVG] If clipPath has multiple elements, clip-path coordinate system is wrongly scaled in high DPI

[Fujii Hironori]

Created attachment 371919 [details]
test case

[cairo][SVG] If clipPath has multiple elements, clip-path coordinate system is wrongly scaled in high DPI

This test case is created by doubling a rect element in clipPath element of svg/foreignObject/clip.html.

[Fujii Hironori]

Created attachment 371920 [details]
[Screenshot] WinCairo port in 150% DPI display

[Fujii Hironori]

Created attachment 371925 [details]
WIP patch

[Carlos Garcia Campos]

Comment on attachment 371925 [details]
WIP patch

View in context: https://bugs.webkit.org/attachment.cgi?id=371925&action=review

> Source/WebCore/platform/graphics/cairo/PlatformContextCairo.cpp:88
> +        // Reset the current matrix because the mask surface doesn't have a matrix.
> +        cairo_matrix_t matrix;
> +        cairo_get_matrix(m_cr.get(), &matrix);
> +        cairo_identity_matrix(m_cr.get());
>          cairo_mask_surface(m_cr.get(), maskInformation.maskSurface(), maskRect.x(), maskRect.y());
> +        cairo_set_matrix(m_cr.get(), &matrix);

This works for svg, but not for other users of GraphicsContext::clipToImageBuffer() like shadow blur, for example. It seems that svg is the only one using absolute coordinates. Removing:

AffineTransform absoluteTransform = SVGRenderingContext::calculateTransformationToOutermostCoordinateSystem(renderer);

from RenderSVGResourceClipper::applyClippingToContext and using the identity fixes the test case too. Or keeping the absolute transform but setting the device scale factor in the image buffer cairo surface.

[Carlos Garcia Campos]

You can try with fast/box-shadow/box-shadow-transformed.html for example

[Carlos Garcia Campos]

*** This bug has been marked as a duplicate of bug 198746 ***