Bug 68899 – [CG] Both ShadowBlur and CG Shadow are applied to the rect in GraphicsContext::fillRect()

• Status: RESOLVED
• Resolution: INVALID
• Component: SVG

[Renata Hodovan]

Original code:

    bool drawOwnShadow = !isAcceleratedContext() && hasBlurredShadow(m_state) && !m_state.shadowsIgnoreTransforms; // Don't use ShadowBlur for canvas yet.
    if (drawOwnShadow) {
        float shadowBlur = m_state.shadowsUseLegacyRadius ? radiusToLegacyRadius(m_state.shadowBlur) : m_state.shadowBlur;
        // Turn off CG shadows.
        CGContextSaveGState(context);
        CGContextSetShadowWithColor(context, CGSizeZero, 0, 0);

        ShadowBlur contextShadow(FloatSize(shadowBlur, shadowBlur), m_state.shadowOffset, m_state.shadowColor, m_state.shadowColorSpace);
        contextShadow.drawRectShadow(this, rect, RoundedRect::Radii());
    }

    CGContextFillRect(context, rect);


After some debugging it seems that the shadow applied twice both with ShadowBlur and CGShadow.
We halved the rectangle to emphasize this effect:

    // Was CGContextFillRect(context, rect);
    FloatRect tmp2 = FloatRect(rect.x() + rect.width() / 4, rect.y() + rect.height() / 4, rect.width() / 2, rect.height() / 2);
    CGContextFillRect(context, tmp2);

We attached two pics. In without_contextShadow.png the drawRectShadow was commented out while it was enabled on with_contextShadow.png.
The strange thing was the shadow is still drawn when the drawRectShadow was commented out.
Any idea?

[Renata Hodovan]

Created attachment 108840 [details]
with_contextShadow.png

[Renata Hodovan]

Created attachment 108841 [details]
without_contextShadow.png

[Tim Horton]

I'm a bit confused. Where's the testcase; how can I reproduce this? Or is this in code you're currently working on?

Anyway, how are you applying the shadow? -webkit-svg-shadow? If it's -webkit-svg-shadow, that gets applied via a transparency layer that gets created (in SVGRenderSupport::prepareToRenderSVGContent) whenever you first hit the -webkit-svg-shadow'd element, so each element has no need to draw its own shadow.

[Renata Hodovan]

(In reply to comment #3)
> I'm a bit confused. Where's the testcase; how can I reproduce this? Or is this in code you're currently working on?

> Anyway, how are you applying the shadow? -webkit-svg-shadow? If it's -webkit-svg-shadow, that gets applied via a transparency layer that gets created (in SVGRenderSupport::prepareToRenderSVGContent) whenever you first hit the -webkit-svg-shadow'd element, so each element has no need to draw its own shadow.

The test case was a reduced version of svg/css/group-with-shadow.svg. It uses -webkit-svg-shadow property. I faced this problem while I was working on a new renderer for SVGElements which painted with the shape's own painter without path's one. So if I tried to fill a rectangle with the platform dependent fillRect() it applied both of the shadows.

[Simon Fraser (smfr)]

Why is SVG different from CSS here? CSS doesn't have this issue.

[Renata Hodovan]

(In reply to comment #5)
> Why is SVG different from CSS here? CSS doesn't have this issue.

I don't know exactly the reason but it seems that doesn't matter if I turn out the shadow drawing it still will be painted. I guess it maybe related to context redirections...

[Dirk Schulze]

rene, could you upload a test case please? Is this still the case?

[Simon Fraser (smfr)]

Still need a testcase.

[Brent Fulgham]

It's difficult to confirm this bug without a test case. We don't believe there is an ongoing issue here. If you do feel there is a problem, please REOPEN this bug and include a test case illustrating the issue.