   "Rotated" sampling
  I have 4 vertices making a quad, and the mapping coords of such quad are [(0,0),(1,0),(1,1),(0,1)]I can't touch those mapping coords, yet I need to render the quad with texture "rotated" of 0,90,180 or 270 degrees according to a certain switch.Could it feasible by somehow fiddling with coords in the vertex shader without having to use a switch/case?I can't think of a way actually.   
  Supply a matrix to the shader to transform your texture coordinates, similar to the texture matrix in the fixed function set.glMatrixMode(GL_TEXTURE);glLoadIdentity();glRotate(0, 0, 1, angle);You can rotate by any arbitrary angle, not just multiples of 90 degrees.   ;  That's a simple and elegant solution I didn't think of!But I fear it won't easily apply to my case, which I have simplified a bit too much in my explanation. It's not really just a quad, it's going to be a huge batch of quads actually, hundreds of quads infact, and each one could be rotated in a different way. Instancing perhaps?   