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Posted: **Mon Feb 04, 2013 8:49 pm**

Hello.

I'd like to make textures combination using 2 textures (double-texturing) but I never get a good result.
I've found a tutorial explaining some of the requirements :
http://www.informit.com/articles/articl ... 9&seqNum=6

It seem well explained so, I did this :

Code: Select all

      glActiveTexture(GL_TEXTURE0);
      glEnable( GL_TEXTURE_2D );
      TrueIndex = MyImagePTR->TrueImageIndex;
      glBindTexture( GL_TEXTURE_2D, ImageTexture[ TrueIndex ] );
      glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE );

      UpdateMyImagePTR( mRaster[ RasterID ].iRaster );
      glActiveTexture(GL_TEXTURE1);
      glEnable( GL_TEXTURE_2D );
      TrueIndex = MyImagePTR->TrueImageIndex;
      glBindTexture( GL_TEXTURE_2D, ImageTexture[ TrueIndex ] );
        switch( Transparency ){
          case 0:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );
           break;
          case 1:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE );
           break;
          case 2:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_ADD );
           break;
          case 3:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_ADD_SIGNED );
           break;
          case 4:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_INTERPOLATE );
           break;
          case 5:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_SUBTRACT );
           break;
          case 6:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DOT3_RGB );
           break;
          case 7:
            glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DOT3_RGBA );
           break;
         }
      glActiveTexture( GL_TEXTURE0 );

In all case I get the same result. the combination of the 2 textures but really dark.
Excepted case 4 for transparency where I only get the 2nd texture really dark.
Do you know exactly what can cause this ?

The wanted result is absolut adding of RED, GREEN & BLUE.
For example:
Texture 1 : RGB : 64, 80, 100
Texture 2 : RGB : 64, 10, 10
Result : RGB : 128, 90, 110
Do you understand ?
Is there someone that know how I can do this ?

EDIT : I've made changes to setup textures like opengl samples do. (source code edited)
in all case the texture remain dark excepted one where it appear bright but the result is not the one wanted.

Thank you.

Regards,
AmiDARK

Posted: **Mon Feb 04, 2013 10:55 pm**

You need to set the TEXTURE_ENV_MODE to GL_COMBINE, and then set the GL_COMBINE_RGB and GL_COMBINE_ALPHA to the combiner functions you want.

GL_TEXTURE_ENV_COMBINE can only take the values MODULATE, DECAL, BLEND, REPLACE or COMBINE. If you set it to COMBINE, it will be able to use the GL_COMBINE_RGB and GL_COMBINE_ALPHA functions for multitexturing. If you want to add two textures, you would set

glActiveTexture( GL_TEXTURE0 );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE );
glActiveTexture( GL_TEXTURE1 );
glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE );
glTexEnvi( GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_ADD );
EDIT: to be sure, you should also add
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PREVIOUS );
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE );

Posted: **Mon Feb 04, 2013 11:18 pm**

Thank you Hans for your answer.

I will test this now

Regards,
AmiDARK

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