Bug 70789 – Optimize canvas fills / drawImage when covering entire canvas

• Status: RESOLVED
• Resolution: FIXED
• Component: Canvas

[Ben Wells]

When compositing fills / drawImage calls in canvas, and the composite mode is Source-In, Source-Out, Destination-In, Destination-Atop or Copy, the canvas is cleared. For all of these modes apart from Copy a temporary buffer is also used. If the fill / drawImage is covering the entire canvas we can optimise away the clear and the use of a temporary buffer.

[Ben Wells]

Created attachment 113422 [details]
Patch

[Ben Wells]

It would be nice to do the same optimization for filling a path, but there doesn't seem to be any easy way to see if a path contains a rectangle.

[Stephen White]

Comment on attachment 113422 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=113422&action=review

Looks good.  Thanks for implementing this!  r=me

> Source/WebCore/html/canvas/CanvasRenderingContext2D.cpp:1566
> +    Path transformedPath;
> +    transformedPath.addRect(rect);
> +    transformedPath.transform(state().m_transform);
> +
> +    IntRect canvasRect(0, 0, canvas()->width(), canvas()->height());
> +    return transformedPath.contains(canvasRect.minXMinYCorner()) && transformedPath.contains(canvasRect.minXMaxYCorner())
> +        && transformedPath.contains(canvasRect.maxXMinYCorner()) && transformedPath.contains(canvasRect.maxXMaxYCorner());

This looks fine, but I'm wondering if it would be easier to use FloatQuad:

FloatQuad quad(rect);
FloatQuad canvasQuad(FloatRect(0, 0, canvas->width(), canvas->height()));
return state().m_transform.mapQuad(quad).containsQuad(canvasQuad);

OTOH, I've never actually tried it, so feel free to go with what you've already got.

[Ben Wells]

Created attachment 113571 [details]
Patch using FloatQuad

[Ben Wells]

Comment on attachment 113571 [details]
Patch using FloatQuad

Using FloatQuad is much nicer. Thanks for the tip!

[Stephen White]

Comment on attachment 113571 [details]
Patch using FloatQuad

Looks great.  r=me

[WebKit Review Bot]

Comment on attachment 113571 [details]
Patch using FloatQuad

Clearing flags on attachment: 113571

Committed r99257: <http://trac.webkit.org/changeset/99257>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.