Multitexturing is darkening the entire scene!

Question

I've implemented a scene using 3 quads, A, B, and C. Quad C is behind quad B. Quad B sits on top of Quad A.

All quads are using the same texture with the exception of Quad B. Quad B makes use of an alpha map and the base texture all the other Quads are using.

The code sample below is how I'm drawing Quad B with fixed function multi-texturing.

GLuint alphaGLTexture; 
SDL_SurfaceToGLTexture(aTexture, &alphaGLTexture);

GLuint baseGLTexture;
SDL_SurfaceToGLTexture(baseTexture, &baseGLTexture);

glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);
glBindTexture (GL_TEXTURE_2D, alphaGLTexture);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_REPLACE);

glActiveTexture(GL_TEXTURE1);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, baseGLTexture); 

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_PREVIOUS);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE2_RGB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_ALPHA);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);

glTranslatef(0.0f, 0.0f, 0.0f);

double u_coord = 0.0f, v_coord = 0.0f;

// Renders Quad B
glActiveTexture(GL_TEXTURE0)
glBegin(GL_QUADS);

// remainder of code modifies u_coord, v_coord and draws the other glVertex3f's.
glMultiTexCoord2f(GL_TEXTURE0, u_coord, v_coord);
glMultiTexCoord2f(GL_TEXTURE1, u_coord, v_coord);
glVertex3f(posax, posay, posaz);

When I apply a multitextured alpha map to Quad B, the textured Quads A and C change color and end up darker than Quad B.

When I remove any mention to GL_TEXTURE1 everything renders nicely, no dimming, though I lose my alpha mapping on Quad B.

Any recommendations or tips? Is there something wrong with my glTexEnvi calls?

score 1 · Accepted Answer · answered Jun 29 '11 at 21:04

1

You need to disable all of the texture units so that none of the textures influences the rest of the scene. By the looks of your code you probably just forgot to keep track of your states.

Add

glActiveTexture(GL_TEXTURE0);
glDisable(GL_TEXTURE_2D); // or whatever texture target used

glActiveTexture(GL_TEXTURE1);
glDisable(GL_TEXTURE_2D); // or whatever texture target used

glActiveTexture(GL_TEXTURE…);
glDisable(GL_TEXTURE_2D); // or whatever texture target used

answered Jun 29 '11 at 21:04

datenwolf

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is calling glActiveTexture(GL_TEXTUREN); synonymous with calling glEnable(GL_TEXTURE_2D); ? – ct_ Jun 30 '11 at 02:46
@ct: No, it switches the currently active texturing unit, glEnable/glDisable(GL_TEXTURE_…) enables/disables the active texturing unit. This quite like glMatrixMode. – datenwolf Jun 30 '11 at 07:18

score 0 · Answer 2 · answered Jun 29 '11 at 20:59

0

Try disabling texture unit 1 if you aren't using it for your other quads:

// draw Quad B
....

glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);

glActiveTexture(GL_TEXTURE1);
glDisable(GL_TEXTURE_2D);

// draw Quad A
.....

// draw Quad C
.....

answered Jun 29 '11 at 20:59

genpfault

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score 0 · Answer 3 · answered Jul 01 '11 at 19:24

You could enable and disable GL_TEXTURE_2D each frame depending on whether each texture unit requires it (like other answers have suggested). Alternatively, you could just unbind the textures that you don't need, which should be much faster:

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D,0);

glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D,0);

glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D,0);

glActiveTexture(GL_TEXTURE0); //make sure to set the active texture unit back to 0

Multitexturing is darkening the entire scene!

3 Answers3