Wednesday, October 24, 2007

Procedural Sphere

While implementing my Sky Dome for atmospheric Scattering a number of issue quickly became noticeable. A sphere generated using the OpenGL function gluSphere or loaded from a mesh file had vertex compression at the poles. This usually causes texture compression/distortion which is naturally very undesirable.

To maintain Decade's procedural capability and to remove the issues with the previous implementation I created my own Sphere function by recursively subdividing a cube until the required resolution was achieved.

Below the two solutions can be seen side by side. On the left is the Sphere created with gluSphere or loaded from a file. The vertex compression is immediately obvious. The size of the face depends on which segment it exists, with faces getting smaller closer to the poles. On the right is my procedurally generated sphere. As you can see there is no vertex compression at the pole. In fact no pole is visually obvious. Due to the subdividing nature of the algorithm each face in the sphere is the exact same size.

I believe I may have achieved allot more than just creating a sky dome with this implementation. Creating a universe with procedural planets has always been on the wish list for Decade but I never knew where to begin. The recursive subdivision appears to be an ideal solution for this. It has level of detail and efficient culling properties automatically built in.

The level of the quad tree rendered defines the level of detail of the planet. Since the root of the planet is 6 quads, it is easy to bounds check these against the frustum and quickly remove unseen areas of the planet and the same process can be repeated for each of the child levels of the quad tree.

By using the above algorithm along with some height maps I believe rendering a full planet should be possible. I look forward to the day when I can roam a planet in Decade then jump in a space ship, fly away and land on another planet.

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