P-152: Virtual World Concept Update 128: Planet-sized Terrain: Part 7

I have looked at the spherical terrain using the wireframe viewer tool in the T3D editor, and, when scaled to realistic planetary sizes, it seems that the remaining issues that I am seeing are due to Z-fighting.

I think that given the huge distances involved, some of the vertices from behind the terrain (the other side of the planet) are being rendered in front of it. What I have been doing over the last few days is experimenting with various scaling factors and coordinate systems in order to come up with a way to reliably cull nodes that are not relatively close to the player. I believe I have succeeded in doing this, and it involves first changing the players scale so that it matches the terrain (the player is in 32-bit space, typical for an object in T3D, the spherical terrains nodes are between -1 and +1). Then, I scale both to by the radius of the planet (6137000 for Earth). I can then get the distance between them.

I am tentatively hoping that by removing all but the nearest nodes, the Z-fighting issues will disappear (since the distance from the nearest node to the furthest is much less, and there are no no nodes in front of each other). This won’t really solve the problem, but it should eliminate any noticeable rendering issues. I can implement a better solution later. Since the player is close to the origin always, there should be no jitter at all.

If this doesn’t work, I will need to find some way of translating the node position from 64-bit into 32-bit space. This is not just a simple case of scaling them down, since a simple scale operation would change the radius of the sphere, which would in effect change the entire terrain’s structure. I will probably have to do something like this eventually anyway, to completely solve the issues causes by the huge view distances.

Even if this idea does work, I will still need to implement the floating origin system which will actually allow the player to travel around the surface of the terrain, and then I will need to implement the distance scaling algorithm that will provide a seamless surface-to-space transition fro the terrain.