Thursday, December 13, 2012

Tessellation based on distance

As mentioned previously, I got my tessellation working, but it tessellated the entire geometry. So then I went on to implement a distance based tessellation. The goal was to have multiple levels of tessellation based on distance from camera. So I separated out the distance between the near and far planes and did a gradual tessellation based on distance. This speeds up the frame rate of display. It increased quite a bit. I was getting about 6-9 fps which increased to around 40-50 fps.

Then I realized that I was just basing my tessellation on z-distance and the terrain was getting tessellated on the left and the right. I think clipping happens later, so the terrain is tessellated even if it is out of view, though it doesn't get rasterized. So I then went on to calculate which vertices actually lie in the frustum of the camera and made sure that only those vertices get tessellated. Even this gave me a 4-5 fps increase.

The image and video below shows the tessellation of the terrain. This is just a constant tessellation for display, but I have modified it to tessellate to certain distance and then keep on decreasing tessellation as we move further away.

Tessellation based on distance from camera

Video shows tessellation based on distance from camera

Next steps:
  • Ambient Occlusion
  • Screen space normals

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