Re: [pygame] Unexpect blit behavior when using BLEND_ADD

[Lenard Lindstrom <len-l@xxxxxxxxx>]

Marcus von Appen wrote:
> On, Wed Apr 16, 2008, Lenard Lindstrom wrote:
>
>   
> > I was trying out BLEND_ADD with blit to see if an alpha plane could be 
> > added to a surface with alpha's zero. Here is the trial session:
> >     
> [...]
>
> Both surfaces contain alpha, so only alpha blending will be applied. The
> BLEND_* args only work for cases where alpha blending cannot be
> applied.
> Should we change this to take alpha into account for the BLEND_* args as
> well and only apply the default alpha blending, if no BLEND_* args are
> passed?
>
>   
The documentation is vague on this. It just says that BLEND_ flags are 
optional. Nothing is mentioned about them being ignored. For alpha 
surfaces a blend may be useful for doing shadow effects. Such effects 
require extracting and altering the alpha plane. Want to make a shadow 
for antialiased text. Extract the alpha and apply to an all black 
surface. Right now surfarray must be used to do this in a practical way. 
Otherwise it would have to be done per-pixel with get_at/set_at.

--
Lenard Lindstrom
<len-l@xxxxxxxxx>