title: Animating a texture across a surface in OpenGL
body: <p>I'm working with the iPhone OpenGLES implementation and I wish to endlessly scroll a texture across a simple surface (two triangles making up a rectangle).  This should be straightforward, but it's not something I've done before and I must be missing something.  I can rotate the texture fine, but translate does not work at all.  Do I have a minor implementation issue or am I doing something fundamentally wrong?</p>
  
  <pre>
   // move texture
   glMatrixMode(GL_TEXTURE);
   glPushMatrix();
   glLoadIdentity();
  
      // increment offset - no reset for demo purposes
   wallOffset += 1.0;
  
      // move the texture - this does not work
   glTranslatef(wallOffset,wallOffset,0.0);
  
      // rotate the texture - this does work
   //glRotatef(wallOffset, 1.0, 0.0, 0.0);
  
   glMatrixMode(GL_MODELVIEW);
  
   glBindTexture(GL_TEXTURE_2D, WallTexture.name);
   glTexCoordPointer(2, GL_FLOAT, 0, coordinates);
  
   // simple drawing code
   glNormalPointer(GL_FLOAT, 0, normals);
   glVertexPointer(3, GL_FLOAT, 0, vertices);
   glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
  
      // push matrix back
   glMatrixMode(GL_TEXTURE);
   glPopMatrix();
   glMatrixMode(GL_MODELVIEW);
  </pre>