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Re: GL_COMBINE 2 Textures

Subject: Re: GL_COMBINE 2 Textures
From: bsupnik <email@hidden>
Date: Wed, 03 Nov 2004 13:50:35 -0500
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Hi Lorenzo,

I'm not sure that these are your problems, but here are a few issues to look at:

- The combine extension doesn't guarantee that you can use any texture as any source to a combine op.[ You do

>     glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE0);

I don't know about the crossbar extension but without it this is illegal - use GL_PREVIOUS as your source to get the last texture.

- It's been my experience that you need to specify every aspect of the combine op...this may just be me being paranoid, but I would consider putting _something_ in the alpha channel for this.

- I don't think 'combine' will mix 100% of A + 30% of B - it will give you 70% of A and 30% of B. To get that, bind your constant (0.3) to input 2 and your two textures (GL_PREVIOUS and GL_TEXTURE) to input 0 and 1.

- A way to get 30% + 100% with two tex units (which you might as well do anyway since you have to use two tex units to do do two textures) is to put the 30% texture in the first unit and modulate it with a constant of 0.3. Then put the second tex in unit one and use add.

- You can accomplish the above without using GL_COMBINE at all, as long as it's all you want, just use 0.3 for your color, GL_MODULATE and GL_ADD as the tex modes.

This all gets a lot trickier if you want (100% of A + 30% of B) * local_lighting...

*Cheers*
Ben

Lorenzo wrote:

Hi,
I am trying to mix 2 textures. 100% of the first texture + 30% of the second
texture. I wrote the following code, but I get bad results. Do you know
where is my mistake?
    glActiveTexture(GL_TEXTURE0);
    glEnable(GL_TEXTURE_RECTANGLE_EXT);
    glBindTexture(GL_TEXTURE_RECTANGLE_EXT, textures_rect[0]);
    glActiveTexture(GL_TEXTURE1);
    glDisable(GL_TEXTURE_RECTANGLE_EXT);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, textures_2D[0]);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE); glTexEnvf(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE); glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE0); glTexEnvf(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR); // Point A GLfloat blendColor[4] = {1.0, 1.0, 1.0, 0.3}; glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, blendColor); glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_CONSTANT); glTexEnvf(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_ALPHA); // Point B glTexEnvf(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE1); glTexEnvf(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_SRC_COLOR);
I even inverted the point A with the point B but I get bad results again.
Best Regards

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