Smooth collision detection isn''t really so bad when you get a few things working..there are many ways you could optimize terrain collision, but here''s a general all purpose method of smooth collision detection that should work in several implementations..

First of all you have to determine which surface you are near enough to clip against..then clip the model position against that surface in 3d space..(you will have to add some height offset to the model unless the origin is at the bottom)..

Let''s assume that the model position is a single vertex(you can easily use this same code for multiple vertices)..
You would also need to determine minimum_clipping_distance..this is how close you can get to a surface before it ''pushes back''..this distance should be slightly larger than the model''s average movement per frame...

Here''s how you would clip against a surface and make it smooth:

Get the distance from the vertex to the plane of the surface..let''s call this distance_from_plane..
If distance_from_plane is greater than your minimum_clipping_distance, there is no collision necessary..
IF NOT
You need to find out how far into this clipping region you are..let''s call this distance_inside_clipping_zone..

distance_inside_clipping_zone = (minimum_clipping_distance-distance_from_the_plane)

that was easy..
now that we know how far into the clipping region we are, we just need to relocate the model..

model.x += surface.xnormal*distance_inside_clipping_zone;
model.y += surface.ynormal*distance_inside_clipping_zone;
model.z += surface.znormal*distance_inside_clipping_zone;

WARNING!!
(you may have to -= if you are colliding with the back of a surface..front/back test is easy to check, just subtract values instead of adding)..
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WHY THIS IS COOL

No matter how you come at a surface, it will always push you out a consistent distance..add a constant gravity drop and the model will actually slide down ramps on it''s own..when moving forward up a ramp, your forward motion is hampered depending on the angle of the surface..when you walk into a wall you will slide smoothly along..

The math isn''t so bad either..assuming you''ve already got normals for your surfaces, here''s all you have to do:

Calculate the distance from a point to a plane..
Subtract that from the minimum_clipping_distance..
To the model vertex, add the surface normal multiplied by the distance inside the clipping region..

If you need help with any of the math feel free to email me
Enjoy,
-MM


"Like all good things, it starts with a monkey.."