<meter> doesn't update rendering when its value is changed

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Ian 'Hixie' Hickson]

Click the button in the testcase:
   http://www.hixie.ch/tests/adhoc/html/forms/meter/001.html

It should update the rendering. It doesn't. For some reason, clicking the meter itself does cause it to repaint with the new value.

[Dominic Cooney]

Debugging this is tricky because shifting focus from Safari to the debugger will cause this to repaint. Modify the repro to update the value in a timeout and switch focus away from Safari before the timeout fires.

The relevant part of the tree looks like this:

BODY    0x1085106c0
        …
        P       0x108510e90
                #text   0x108510fe0 "\n "
                METER   0x1085111f0
                        #shadow-root    0x1085113a0
                                DIV     0x1085112a0
*                                       DIV     0x108511320 STYLE=width: 30%;

Style recalc gets down to the DIV, but it opts to not update its style in Element::recalcStyle, despite needing recalc, because hasParentStyle is false. But I am not sure how inline style recalc normally works :)

[Dominic Cooney]

MeterShadowElement probably claims it doesn’t need a renderer in rendererIsNeeded, and this means the parent DIV of the value doesn’t have a renderer and hence doesn’t have a style. I note that adding <style>meter { -webkit-appearance: none; }</style> makes the bar update as expected.

Is the right thing here to use the Node::nonRendererRenderStyle hook that HTMLOptionElement uses?

[Hajime Morrita]

Created attachment 107981 [details]
Patch

[Hajime Morrita]

Thanks for Dominic's investigation, the fix itself is trivial.

[Dimitri Glazkov (Google)]

Comment on attachment 107981 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=107981&action=review

> Source/WebCore/html/HTMLMeterElement.cpp:232
> +    if (RenderObject* render = renderer())
> +        render->updateFromElement();

Aren't we doubling the rate of repaints for shadow DOM-based meter?

[Hajime Morrita]

(In reply to comment #5)
> (From update of attachment 107981 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=107981&action=review
> 
> > Source/WebCore/html/HTMLMeterElement.cpp:232
> > +    if (RenderObject* render = renderer())
> > +        render->updateFromElement();
> 
> Aren't we doubling the rate of repaints for shadow DOM-based meter?
I think the impact is little because actual repaints are deferred and batched into
single paint() call even though repaint() call will increase.

[Hajime Morrita]

Created attachment 108109 [details]
Patch for landing

[Hajime Morrita]

Comment on attachment 108109 [details]
Patch for landing

I should land this manually since bot cannot see this.

[Hajime Morrita]

Committed r95599: <http://trac.webkit.org/changeset/95599>