Bug 94400 – [chromium] Random noise around text in FPS HUD

• Component: WebCore Misc.
• Status: RESOLVED FIXED

[Vangelis Kokkevis]

This is the result of an missing clear operation in the canvas used to store the text atlas.

[Vangelis Kokkevis]

Created attachment 159240 [details]
Patch

[James Robinson]

Comment on attachment 159240 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=159240&action=review

> Source/WebCore/platform/graphics/chromium/CompositorHUDFontAtlas.cpp:68
>      atlasContext.setFillColor(Color(0, 0, 0, 0), ColorSpaceDeviceRGB);
> -    atlasContext.fillRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE));
> +    atlasContext.clearRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE));

how is clearRect() different from fillRect() with color(0, 0, 0, 0) ?

do you still want to set the fill color when calling clearRect()?

[Vangelis Kokkevis]

(In reply to comment #2)
> (From update of attachment 159240 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=159240&action=review
> 
> > Source/WebCore/platform/graphics/chromium/CompositorHUDFontAtlas.cpp:68
> >      atlasContext.setFillColor(Color(0, 0, 0, 0), ColorSpaceDeviceRGB);
> > -    atlasContext.fillRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE));
> > +    atlasContext.clearRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE));
> 
> how is clearRect() different from fillRect() with color(0, 0, 0, 0) ?

The default transfer mode for GC is "source-over" (essentially a blend with whatever was in the background) which means with fillRect we're drawing a transparent rect over whatever was already there, which has no effect. 

clearRect sets the transfer mode to clear which does the job.

> 
> do you still want to set the fill color when calling clearRect()?

It's used by the Skia code when setting the paint, so I assume that yes, it's needed. Presumably you could clear to any color.

[WebKit Review Bot]

Comment on attachment 159240 [details]
Patch

Clearing flags on attachment: 159240

Committed r125961: <http://trac.webkit.org/changeset/125961>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.