Question

I am creating a program which draws an object, which needs to “point” toward the mouse. To do so I want to draw the image rotated.

I have this code for drawing the object:

glBindTexture(GL_TEXTURE_2D,img.getTextureID());
glBegin(GL_QUADS);
glTexCoord2f(0,0);
glVertex2f(x-r,y-r);
glTexCoord2f(1,0);
glVertex2f(x+r,y-r);
glTexCoord2f(1,1);
glVertex2f(x+r,y+r);
glTexCoord2f(0,1);
glVertex2f(x-r,y+r);
glEnd();

Pretty basic. But I was having a hard time finding out how to rotate the texture, or draw the texture rotated.

Answer 1

To elaborate on @genpfault’s answer:

If you want your texture to rotate around its center, you need to draw it so its center is at (0,0). Try something like this:

glPushMatrix();
glTranslatef(x,y); // move to the proper position
glRotatef( angle, 0, 0, 1 ); // now rotate

glBindTexture(GL_TEXTURE_2D,img.getTextureID());
glBegin(GL_QUADS);
glTexCoord2f(0,0);
glVertex2f(-r,-r);
glTexCoord2f(1,0);
glVertex2f(+r,-r);
glTexCoord2f(1,1);
glVertex2f(+r,+r);
glTexCoord2f(0,1);
glVertex2f(-r,+r);
glEnd();

glPopMatrix(); // pop off the rotation and transformation

Note that glRotatef‘s angle is in degrees, not radians.