RE: [Algorithms] Environment map texture blending question.

[Evan H. <eh...@at...>]

I assume that you are looking to do this with the texture blending stages
and not the alpha blender. The primary difficulty appears to be getting the
routing to work. On a Radeon with OpenGL and only the Texture_Env_Combine
extension, you can do the following:

Texture Stage 0:
Bind Base Texture
TexEnvMode = REPLACE

Texture Stage 1:
Bind Env Map Texture
TexEnvMode = COMBINE
COMBINE_RGB = INTERPOLATE
Source0_RGB = Previous
Source1_RGB = Texture
Source2_RGB = Previous

Texture Stage 2:
Bind Dummy Texture ( 1x1 white square)
TexEnvMode = COMBINE
COMBINE_RGB = MODULATE
Source0_RGB = Previous
Source1_RGB = Primary_color

 A similar setup should apply under D3D or other cards.

	-Evan

-----Original Message-----
From: Ratcliff, John [mailto:jra...@ve...]
Sent: Friday, January 05, 2001 3:53 PM
To: 'gda...@li...'
Subject: [Algorithms] Environment map texture blending question.


For those of you familiar with the various blending modes on 3d cards I have
a question to ask.  Perhaps this should be obvious, but I'm certainly
missing it.

What I want to do is combine an environment map with a base texture on a
model.  That's fairly straightforward.  However, I want the environment map
to be blended relative to the alpha channel found in the texture built for
the base model.  In this way to control per-pixel reflectivity.  After these
have been combined I then want to attenuate the result by the diffuse color
component from lighting solution.  That way the shiny bits are still dark if
the base model is dark.   If the envinronment map doesn't also absorb the
same diffuse lighting as the base texture it no longer looks like a
refelction and instead looks like a plastic coating oversaturating the
object.

Either of these two is fairly easy to do.  To combine the environment map
with the base texture, with a modulated blend based on the base textures
alpha channel is easy to do, but it doesn't attenuate by the diffuse.
Likewise you can combine the environment map and the base texture and apply
a diffuse to both, but *not* have the selective alpha blend.  At least I've
been able to get each case to work seperately but not combined.

This is assuming a two texture stage pipeline is available and we want to do
this in one pass.

Ideal equation:  ( (BaseTextureColor * (1 - BaseTextureAlpha) ) + (EnvMap *
BaseTextureAlpha ) * Diffuse

Anybody know the sequences of blend modes you set up using OGL or D3D to
make this happen?

Thanks,

John

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