View Full Version : help me with GL_EXT_texture_env_combine?!
02-24-2004, 09:24 AM
i'm trying to use texture_env_combine to combine an alpha map texture with an RGB texture. I'm using it for a landscape, to smoothly blend multiple layers together. I can't figure out how to set up each stage to blend. I'm using a TNT card, so I have to draw in multiple passes. Can anyone help me? I can't get on the internet much, so if someone could maybe write up some pseudo-code and email it to me or email me with your reply, that'd be great. thanks for any help.
You should check out opengl 1.5 specs, there's some hint on how to use the combine environeament.
There's a couple of things you have to do. First you set the COMBINE method for current texture with :
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE );
then you'll have to choose a texture blending equation for current texture with :
glTexEnvf( GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE );
This sets an equation for blending. You can find details for equation on openglspecs.
In this case, GL_INTERPOLATE is something like :
Arg0*Arg2 + Arg1*(1-Arg2)
Where you set your desired Argn with
strings like :
glTexEnvf( GL_TEXTURE_ENV, GL_SOURCEn_RGB, GL_PREVIOUS );
glTexEnvf( GL_TEXTURE_ENV, GL_OPERANDn_RGB, GL_SRC_COLOR );
Again, for more details check the specs.
Hope it was helpful somehow!
02-26-2004, 01:56 PM
thanks for replying
i finally figured it out. i didn't even need the combine extension! the interpolate wouldn't work when using alpha maps since a TNT can only sample 2 texels per pass. i tried just about every combo with the combine_ext. but turns out that i didn't even need that... silly me...
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