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Re: multitexturing question

I did exactly this in my game, using the third texture unit as a colormap and using the alpha channel as a mixmap, then a fourth unit for a detail texture. Obviously, you should check how many texture units are available and have some sort of fallback. I use colored vertices when a card has only two units, and I don't use a detail texture if a card has three. Also, my implementation, apparently, screws a little with the alpha channel in destination. It's not visible, but it should be taken into consideration.

First, read up on texture_env_combine

http://oss.sgi.com/projects/ogl-sample/registry/ARB/ texture_env_combine.txt


/*
	We're on a system with at least two texture units. We'll
	TEXTURE0 : Primary Texture
	TEXTURE1 : Secondary Texture
	TEXTURE2 : ColorMap / Mixmap
	TEXTURE3 : Detail

	The RGB of TEXTURE2 is used for coloration, and the alpha is used
	to select blending amount.
*/

glActiveTextureARB( GL_TEXTURE0_ARB );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, _primaryTextureID );
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 0.0 );

glActiveTextureARB( GL_TEXTURE1_ARB );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, _secondaryTextureID );
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 0.0 );

glActiveTextureARB( GL_TEXTURE2_ARB );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, _colormapTextureID );

glActiveTextureARB( GL_TEXTURE3_ARB );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, _detailTextureID );
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 2.0f);

/*
	Set up blending modes

	unit0: COMBINE:  TEX1 * TEX2_a + TEX0 * (1-TEX2_a)
*/
glActiveTextureARB( GL_TEXTURE0_ARB );
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_TEXTURE1_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND0_RGB_ARB, GL_SRC_COLOR );

glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE0_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_SRC_COLOR );

glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE2_RGB_ARB, GL_TEXTURE2_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND2_RGB_ARB, GL_SRC_ALPHA );


/*
	unit1: COMBINE:  unit0 * TEX2_rgb
*/
glActiveTextureARB( GL_TEXTURE1_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_MODULATE );

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

glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_TEXTURE2_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_SRC_COLOR );

/*
	before unit2: MODULATE: unit1 * PRIMARY_COLOR
	now: unit2: ADD_SIGNED unit1 & Primary
*/
glActiveTextureARB( GL_TEXTURE2_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_ADD_SIGNED );


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

glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_PRIMARY_COLOR_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_SRC_COLOR );		

/*
	unit3
*/	
glActiveTextureARB( GL_TEXTURE3_ARB );
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_ADD_SIGNED);

glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB,  GL_TEXTURE3_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND0_RGB_ARB, GL_SRC_COLOR );
	
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB_ARB, GL_PREVIOUS_ARB );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB_ARB, GL_SRC_COLOR );



Shamyl Zakariya
  "this is, after all, one of those movies where people spend a great
  deal of time looking at things and pointing."
	From a review of _Fantastic Voyage_

On Mar 21, 2005, at 8:18 AM, Kaveh Kardan wrote:

Does anyone have sample code which shows how to blend 2 textures using a third one as a mask? I have tried various combinations, but none have worked.

I'm assuming a TiBook has enough texture units (3) to handle this.

I'm using Carbon/GLUT.

Kaveh Kardan                 Chief Technologist
email@hidden             Academy for Creative Media
(808)956-5302                University of Hawaii

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 >multitexturing question (From: Kaveh Kardan <email@hidden>)



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