Re: images / alpha-blending

[David Reitter]

On 19 Feb 2006, at 22:47, Richard M. Stallman wrote:

> What is alpha-blending?  What does the feature do?
>
> We don't want Emacs to support features that are limited to a non-free
> system; that would betray the goal we are working for.

An "alpha layer" is a form of "graded transparency layer". With basic  
transparency, you define a bitmask where one bit corresponds to one  
pixel, indicating whether or not the background should be displayed  
in that pixel (rather than a pixel belonging to the actual image). An  
alpha layer assignes a value of higher resolution to each pixel. When  
the image is displayed, the background color for that pixel blends in  
with the image pixel. This produces smooth edges.

Supporting this is not merely a matter for the application (Emacs),  
but also for the graphics device and layers in between. So of course  
it wouldn't make sense to produce an alternative icon set if the  
images required something that isn't and won't be equally supported  
on the free platforms. Hence my question.