Nonlinear perspective transform / warp using heightmap

[oswinso]

Now that we have a heightmap from #672, I think it would be interesting to play with using the height information when doing our projection. Unlike #665, which assumes that the plane is flat, it would be cool to explore using the heights from the heightmap to define some sort of nonlinear transform from the camera's pov and the top down bird's eye view.

Ex. If there's a barrel in front, because we know that the top of the barrel is tall, instead of the bird's eye view containing the sides of the barrel, it will only contain the top of the barrel (since we know that the barrel is tall), resulting in some of the space behind the barrel being blocked and unknown.

I'm not sure about the performance of such a transform, but I think it would be cool to try out.

AC: Image projection using height information to account for nonlinear projections.