Hey; I have a project which does this so far: 1) draws a height mapped terrain 2) disables depth testing, draws a "road" (a single quad), and re-enables depth testing 3) draws some quads to test depth testing Everything works as expected here: the road appears above the terrain, and the quads intersect the terrain as if there were no road overlapping it; however, I'd like the road to change the depth buffer as if depth testing wasn't ever disabled, but still always appear above the terrain. How might I go about this?

solution:

rather than disable the depth test, I changed the depth function to GL_ALWAYS

works perfectly :)