[PD] Gem questions

chris clepper cgc at humboldtblvd.com
Mon Apr 4 08:13:48 CEST 2005

On Apr 3, 2005, at 11:43 PM, vade wrote:

> Hello list.
> 2 quick questions.
> 1) Is there a way to enable an alpha channel for the [color ( message 
> to gemwin? I ask because jitters [erase_color] attribute with an alpha 
> between 0 and 1 allows for interesting trailing effects when geometry 
> is moved, and leaves a gradated trail behind it. Quite nice.

Looks like the alpha is set to 0.0 after the message is received, which 
is an oversight.  You can use GEMglClearColor to set an new color and 
it does handle alpha.

> 2) Is there a way to change blend mode attributes for gemhead objects? 
> Ie force a renderchain to render with one of the 7 source and 7 alpha 
> blending modes that should be available?

The [alpha] object has the basic transparency function.  Rolling your 
own around GEMglBlendFunc might work although the messages for src and 
dst are floats, which might require looking at the GL headers to get 
those values.

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