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Interpolating Between Textures...

Started by HellRaiZer Oct 18, 2003 at 2:00 PM 5 replies 400+ views

Original Post

Oct 18, 2003 at 2:00 PM

[This is the second time posting this, because while i was submitting some changes the thread was screwed up, so i had to repost. I say this because 6 people had saw the previous post, and maybe someone was answering when i destroyed it.] Hi! I have a little question. Is it possible to interpolate between 2 textures with the equation: Result = Tex0 * time + Tex1 * (1.0 - time); using OpenGL (not manually). I''m currently working on a GeForce 256 (2 texture units), so i tried to find something relevant in nVidia''s site. I found a presentation on Register Combiners for GeForce 256, and they mention that the above equation is possible with two texture units. Their equation is: Result = A * B + C * D; My problem is, that i can''t figure out how to map A, B, C, D to Tex0, Tex1, time, 1.0 - time. More simple: How can i setup regcoms to get the result i want. Note that this is my first time playing with register combiners, so if you can explain things a little, i''d be glad! Thanks in advance. HellRaiZer PS. They mention an extension named GL_EXT_texenv_op, but it doesn''t appear in my extension list. Has it been merged to an other extension?

Ilici

Oct 18, 2003 at 2:07 PM

i do it in 2 passes:

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glColor(..., time);

//render pass 1

glColor(..., 1 - time);

//render pass 2

This works fine but it does not interpolate the alpha channel.

I think you can use GL_ARB_texture_env_combine but i've tried it and after many attempts i couldn't get it working.

this is probably the way to use texture_env_combine:
(smth similar to this - i dont know how to setup each texture)

float color[4] = {time, time, time, time};
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, color);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_INTERPOLATE_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB_ARB, GL_SRC_COLOR);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_ONE_MINUS_SRC_COLOR);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_CONSTANT);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB_ARB, GL_SRC_COLOR);

and the same for alpha

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[edited by - Ilici on October 18, 2003 3:13:08 PM]

[edited by - Ilici on October 18, 2003 3:15:10 PM]

HellRaiZer

Oct 18, 2003 at 2:27 PM

Ilici thanks for the code.

I had thought of something similar.
My problem is that i don't know where the second texture comes in! This sounds stupid, isn't it?

Also if someone can explain how we get here from the equations, just to clear things a little, i'd like to hear it.

Thanks again for repling. I'll to see what i can get.

HellRaiZer

[edited by - HellRaiZer on October 18, 2003 3:29:02 PM]

_DarkWIng_

Oct 18, 2003 at 3:08 PM

bind Tex0 to texture unit 0 and Tex1 to texture unit 1. Then use following env_combine on unit 1.


float color[4] = {time, time, time, time};
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, color);

//Arg0 * (Arg2) + Arg1 * (1-Arg2)
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_INTERPOLATE_ARB);

// tex0
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_PREVIOUS_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB_ARB, GL_SRC_COLOR);

// tex1
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_SRC_COLOR);

// interpolation factor
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_CONSTANT); 
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB_ARB, GL_SRC_COLOR);

You should never let your fears become the boundaries of your dreams.

Ilici

Oct 18, 2003 at 3:47 PM

quote:

My problem is that i don't know where the second texture comes in! This sounds stupid, isn't it?

That's exactly my problem

I'll try _DarkWing_'s code now...

The equasion is: Tex0.Color * (1 - c.Color) + Tex1.Color * c.Color
so load c in the texture env color and use the color of the fragments of the 2 textures. and the extnesion does the rest.

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'I wish life was not so short,' he thought. 'Languages take such a time, and so do all the things one wants to know about.' - J.R.R Tolkien
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[edited by - Ilici on October 18, 2003 4:51:14 PM]

[edited by - Ilici on October 18, 2003 4:52:34 PM]

HellRaiZer

Oct 19, 2003 at 1:52 AM

_DarkWing_ thanks for the explanation! I haven't tried it, but it seems reasonable, and i'll do so. Thanks.

What must the enviroment for tex0 be? By default, i set it to modulate. Is this correct?

HellRaiZer

[edited by - HellRaiZer on October 19, 2003 2:54:02 AM]

_DarkWIng_

Oct 19, 2003 at 4:09 AM

quote:
Original post by HellRaiZer
What must the enviroment for tex0 be? By default, i set it to modulate. Is this correct?

I think it should be GL_REPLACE (or GL_DECAL).

You should never let your fears become the boundaries of your dreams.

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