rectangular texture in OpenGL with both width and height POT

Question

I'm trying to use rectangular texture with OpenGL. When the height is equal to the width of the texture, everything looks fine, however, when the height is different than the width the texture looks distorted.

My display function is (h and w are globals storing the height and the width of the image):

Please note that the size of the drawn image doesn't matter. It is distorted regardless of the actual polygon size.

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   glEnable(GL_TEXTURE_2D);
   glEnable(GL_BLEND);
   glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
   glBindTexture(GL_TEXTURE_2D, texName);
   glTranslatef(-2.0f,-2.0f,0.0f);
   glScalef(1.0f/128.0f,1.0f/128.0f,1.0f);
   glBegin(GL_QUADS);
   glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
   glTexCoord2f(0.0, 1.0); glVertex3f(0.0, w, 0.0);
   glTexCoord2f(1.0, 1.0); glVertex3f(h, w, 0.0);
   glTexCoord2f(1.0, 0.0); glVertex3f(h, 0.0, 0.0);

   // Will be distorted also with the following:
   /*glScalef(1.0f/128.0f,1.0f/128.0f,1.0f);
   glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
   glTexCoord2f(0.0, 1.0); glVertex3f(0.0, h, 0.0);
   glTexCoord2f(1.0, 1.0); glVertex3f(w, h, 0.0);
   glTexCoord2f(1.0, 0.0); glVertex3f(w, 0.0, 0.0);*/

   glEnd();
   glFlush();
   glDisable(GL_TEXTURE_2D);
}

I'm loading the texture with:

void *data = LoadBMP("c:\\dev\\64x128_face.bmp");
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
               GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
               GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w,
            h, 0, GL_RGBA, GL_UNSIGNED_BYTE,
            data);

When I'm loading a 64x64 square texture image, it looks fine. However when I'm loading a rectangular texture image, the image looks distorted.

How does OpenGL support rectangular POT texture? What's wrong with my code?

Rock Rock · Accepted Answer · 2010-08-09T10:21:42

Your rect image is 64x128 but you render it with these commands:

   glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
   glTexCoord2f(0.0, 1.0); glVertex3f(0.0, w, 0.0);
   glTexCoord2f(1.0, 1.0); glVertex3f(h, w, 0.0);
   glTexCoord2f(1.0, 0.0); glVertex3f(h, 0.0, 0.0);

where h is height (=128) and w (=64) is width. But you placed height on x (which is width) and width on y (which is height). Maybe try this instead:

   glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
   glTexCoord2f(0.0, 1.0); glVertex3f(0.0, h, 0.0);
   glTexCoord2f(1.0, 1.0); glVertex3f(w, h, 0.0);
   glTexCoord2f(1.0, 0.0); glVertex3f(w, 0.0, 0.0);

rectangular texture in OpenGL with both width and height POT

2 Answers