Re: transparent textures
Angus Dorbie (dorbie++at++multipass.asd.sgi.com)
Thu, 17 Jul 1997 02:20:00 -0700
On Jul 16, 5:26pm, Anita Kishore wrote:
> Subject: transparent textures
> Hello:
>
> I am trying to map an image of a neon sign (created in Photoshop)
> with alpha onto a geometry. The image has the sign in the middle with neon
> like light emanating from it which slowly merges with the blackness around
> the sign. This image with its geometry is in an Inventor file which gets
> loaded into my application through pfiv (BTW : the version of pfiv that I
have
> didn't have transparency enabled, so I added the lines :
>
> if ( numComponents == 4 )
> {
> cbd->dummyGState->setMode(PFSTATE_TRANSPARENCY, PFTR_ON);
> }
>
> in the routine 'getTexture').
>
> Anyway, the problem is that when this texture gets loaded, the neon light
> around the sign appears completely banded with each band having a single
> level of colour. The change in colour from the neon light colour to black
> (completely transparent) is not smooth at all. What else should I set to make
> it smooth?
>
The problem is multisample transparency.
You need transparency of PFTR_BLEND_ALPHA in the neon geostate.
There is a better way for neon lights though.
You actually want to specify a blendfunction of one, one
so get rid of all the alpha in the image and force this
glBlendFunc in a callback again with blended transparency.
Cheers,Angus.
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on Mon Aug 10 1998 - 17:55:37 PDT