What do I have to pass to glBlendFunc to get "source-additive
compositing"?

On Fri, 18 Nov 2011 05:29:31 -0800 (PST)
bob <bob@coolgroups.com> wrote:

> What do I have to pass to glBlendFunc to get "source-additive
> compositing"?

glBlendFunc(GL_ONE, GL_ONE);

On Nov 18, 7:11=A0am, "Wolfgang.Draxinger"
<Wolfgang.Draxin...@physik.uni-muenchen.de> wrote:
> On Fri, 18 Nov 2011 05:29:31 -0800 (PST)
>
> bob <b...@coolgroups.com> wrote:
> > What do I have to pass to glBlendFunc to get "source-additive
> > compositing"?
>
> glBlendFunc(GL_ONE, GL_ONE);

Are you sure it's not:

glBlendFunc(GL_SRC_ALPHA, GL_ONE);

This looks far more correct when I try to recreate the effect.

"bob" <bob@coolgroups.com> wrote in message 
news:a700d640-d201-4874-843f-2ce9db7a9d17@r9g2000vbw.googlegroups.com...
On Nov 18, 7:11 am, "Wolfgang.Draxinger"
<Wolfgang.Draxin...@physik.uni-muenchen.de> wrote:
> On Fri, 18 Nov 2011 05:29:31 -0800 (PST)
>
> bob <b...@coolgroups.com> wrote:
> > What do I have to pass to glBlendFunc to get "source-additive
> > compositing"?
>
> glBlendFunc(GL_ONE, GL_ONE);

|Are you sure it's not:

|glBlendFunc(GL_SRC_ALPHA, GL_ONE);

|This looks far more correct when I try to recreate the effect.



My vote is the latter. I have never ever used GL_ONE, GL_ONE.

jbw 

On Wed, 23 Nov 2011 09:26:43 -0800 (PST)
bob <bob@coolgroups.com> wrote:

> Are you sure it's not:
> 
> glBlendFunc(GL_SRC_ALPHA, GL_ONE);

That would be rather unusual, and I'd call it destination additive.
 
> This looks far more correct when I try to recreate the effect.

You asked for source additive, which I understood as adding the source
as it is. Maybe you meant "pre multiplied alpha", which would be
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);


Wolfgang

On Nov 24, 4:43=A0am, "Wolfgang.Draxinger"
<Wolfgang.Draxin...@physik.uni-muenchen.de> wrote:
> On Wed, 23 Nov 2011 09:26:43 -0800 (PST)
>
> bob <b...@coolgroups.com> wrote:
> > Are you sure it's not:
>
> > glBlendFunc(GL_SRC_ALPHA, GL_ONE);
>
> That would be rather unusual, and I'd call it destination additive.
>
> > This looks far more correct when I try to recreate the effect.
>
> You asked for source additive, which I understood as adding the source
> as it is. Maybe you meant "pre multiplied alpha", which would be
> glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
>
> Wolfgang

I'm trying to figure out what the constant kCAEmitterLayerAdditive
does on Apple.

On Wed, 23 Nov 2011 14:59:09 -0800
"jbwest" <jbwest@acm.org> wrote:

> My vote is the latter. I have never ever used GL_ONE, GL_ONE.

I've used it a number of times. For example when I implemented a
multipass deferred lighting system, where each pass added another
illumination layer.


Wolfgang