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Mona777

Rotating a Texture on a Quad

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Hi I'd be ever so grateful if you know and give the answer to this: I'm trying to put a texture image on a quad, then constantly rotating it around the z axis (say a smiley face on a square). But somehow it keeps tiling the image or distorting it. I've bound the texture to a square in a function called drawTexRect() using glTexCoord2f and glVertex3f with every corner of the square being a bit inside the texture i.e., going from 0.2 to 0.8 , I've experimented with other mappings too. and then: float angle = 0.1, glBindTexture(GL_TEXTURE_2D, tex); glMatrixMode(GL_TEXTURE); glLoadIdentity(); glRotatef(angle, 0.0, 0.0, 1.0); glMatrixMode(GL_MODEL_VIEW); drawTexRect(); then the angle become angle+= 0.1 in my animateFunction so that the image keeps rotating. I've even tried glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T, GL_CLAMP); but the image kept moving out of the quad. Many thanks

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>>but the image kept moving out of the quad.
most likely since the rotation happens around 0,0 but u want it to happen at 0.5,0.5 the center of the quad

anyways better if do the rotation yourself

float c = cosf(rot);
float s = sinf(rot);

glTexCoord2f( 0.5+c, 0.5+s );
glTexCoord2f( 0.5+s, 0.5-c );
glTexCoord2f( 0.5-c, 0.5-s );
glTexCoord2f( 0.5-s, 0.5+c );

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Quote:
Original post by zedz
>>but the image kept moving out of the quad.
most likely since the rotation happens around 0,0 but u want it to happen at 0.5,0.5 the center of the quad


Probably but it's better to use the matrix to deal with animation.

3. glTranslatef(0.5, 0.5, 0.0);
2. glRotatef(angle, 0.0, 0.0, 1.0);
1. glTranslatef(-0.5, -0.5, 0.0);

1. moves the center {0.5, 0.5) at the {0, 0} point.
2. Does the rotation.
3. Restores the translation to where it was.

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