In August of last year I posted a blog entry about terrain cracks. Despite having a theory back then about how to fix this problem I never got around to fixing the issue. A new feature was always more exciting and overtook this development.
Long overdue I have fixed the problem. I will briefly try and recap the issue. Segments of the terrain which are further away from the camera are rendered at a lower level of detail than those which are closer. When a patch gets a distance from the camera the level of details halves. Since every second vertex in the lower level of detail is missing this can result in cracks in the terrain. The image below shows this up close. This situation is not realistic because the patch joins will be a distance away from the camera however even at distance it is possible that artifacts would be visible.
In order to overcome this problem I have removed every second vertex along the edge of a patch which has a higher level of detail. This is all calculated during load time. At run time each neighbour of a patch being rendered is examined and a bitmask is calculated accurately describing the surrounding area. This bitmask is then used to offset into an IndexBuffer array, using the correct buffer with no run time calculation required. A more complete description of this can be found in the previous blog entry.
As can be seen above, there are now no visible joints between patches of differing detail, resulting in a more natural terrain.