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

Mustafizur Rahaman mustaf.here at gmail.com
Wed Jun 1 10:14:20 PDT 2011

Hi Darin,

Thanks for your detailed explanation. Initially we decided to remove the
string as well the enum to fix this issue. But Karthik's patch (we have
already submitted the patch in
https://bugs.webkit.org/show_bug.cgi?id=48290) caused a Chromium build
issue & then we found that this enum is used in
lot of other places. So, we were a little apprehensive about the side effect
of this fix.

Therefore, we submitted another patch where we are returning from the canvas
code itself if the compositing mode is "highlight". We are still waiting for
the review comments.

Similar issue (https://bugs.webkit.org/show_bug.cgi?id=48289 ) we have also
seen for "darker"/CompositePlusDarker (not a valid compositing mode any
more). Can we also remove this as well?


On Wed, Jun 1, 2011 at 9:51 PM, Darin Adler <darin at apple.com> wrote:

> 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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