[cairo] Redoing SOURCE and CLEAR

Owen Taylor otaylor at redhat.com
Wed Aug 17 13:28:14 PDT 2005


On Wed, 2005-08-17 at 11:11 -0700, Carl Worth wrote:

> Another proposal is to also implement IN, OUT, DEST_IN, and DEST_ATOP
> with:
> 
>     (mask IN clip) ? src OP dest : dest
> 
> which would make this the fundamental equation and leave only SATURATE
> as an exception.
> 
> That's appealing as far as having consistent mathematical grounding
> for the rendering equation.
> 
> It's not obvious to me what impact this change would have on usability
> or learnability of the behavior of these four operators. I think there
> are at least two pieces of evidence that would help in this decision:
> 
>  1) Use cases for these operators. That is, English descriptions of
>     things that would like to be achieved, along with corresponding
>     cairo code using one model or the other.
> 
>  2) Two images much like those that Owen previously attached, but
>     showing these 4 operators with both equations.
> 
> I believe Owen is working on #2 right now.

Here is 2) - the columns are:

 IN  OUT   DEST_IN    DEST_OUT   DEST_ATOP

I've included DEST_OUT because I think it helps elucidate how things
should work, though it isn't affected by these changes.

I'll skip adding commentary here and let the images stand on their
own.

Regards,
						Owen

-------------- next part --------------
A non-text attachment was scrubbed...
Name: in-out-destin-destout-destatop-old.png
Type: image/png
Size: 19331 bytes
Desc: not available
Url : http://lists.freedesktop.org/archives/cairo/attachments/20050817/767de62a/in-out-destin-destout-destatop-old-0001.png
-------------- next part --------------
A non-text attachment was scrubbed...
Name: in-out-destin-destout-destatop-new.png
Type: image/png
Size: 24546 bytes
Desc: not available
Url : http://lists.freedesktop.org/archives/cairo/attachments/20050817/767de62a/in-out-destin-destout-destatop-new-0001.png


More information about the cairo mailing list