[webkit-dev] Issue Analysis:48290 [HTML Canvas globalCompositeOperation]

Darin Adler darin at apple.com
Wed Jun 1 09:21:09 PDT 2011

On May 31, 2011, at 11:49 PM, Karthik wrote:

> However, the following comment was mentioned in GraphicsType.h ("    // Note: These constants exactly match the NSCompositeOperator constants of // AppKit on Mac OS X Tiger. If these ever change, we'll need to change the // Mac OS X Tiger platform code to map one to the other. "). So I am little unclear what is the purpose of this CompositeHighLight.

We can remove that comment. It’s obsolete.

I believe the “highlight” compositing mode used to be supported in canvas by WebKit on Mac, but hasn’t been for some time. There’s probably no harm in removing it now.

The fact that the string is “not valid” in the specification isn’t what makes it OK to remove. Please remember that the canvas implementation in WebKit was the first and predates the specification by at least a year. But it’s almost certainly OK to remove this compositing mode because it hasn’t been implemented for quite a while.

There’s still a slim chance that there is some content out there relying on “highlight” being a synonym for “source-over”, but it’s not likely.

One side comment: I think the mapping from strings to the various graphics enums really belongs in the canvas code, not in the platform directory.

    -- Darin

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