Re: Several suggestions for image support

[Jason Rumney]

Kim F. Storm wrote:

> You are right.  Shifting 8 bits here as well on X fixes transparent bg.
> I will commit a fix for X shortly.
>
> However, on W32, it seems that it explicitly scales things to 16 bits
> in both cases.  I cannot test this on W32, so I cannot say what's
> the right thing to do.

The W32 port scales to 16 bits in places because the native Windows 
COLORREF is 8 bits, while Emacs XColor is 16 bits. So in this case, 8 
bits is right, but alpha is currently coming out wrong. I suspect the 
use of COLOREF instead of XColor that you considered a bug when merging 
the image code (see comment around that location) was in fact not a bug.

> Here is an easy way to test it -- after downloading the image you
> mentioned:
>
> (insert-image (create-image "alphatest.png"))
>
> this should result in a light blue image with nice rounded
> edges; a darker blue with rough edges indicates a problem.

On Windows the image comes out with a black background and the image has 
rainbow colored stripes. Non-alpha PNGs look OK.