Collision?

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Original post by treeway in 3d action adventures/platformers like Mario 64 or Prince of Persia : T2T, how is the collision detection achieved. for example how does the prince know to grab a ledge when you jump. Does it use invisible geometry or a grid system like Tombraider 1 ?

Most 3D games these days use some flavour of 'invisible' collision geometry these days. It's usually much less detailed than the geometry used for rendering (since it is 'invisible', the detail level doesn't matter as long as the collidable surface is described adequately enough). Usually the collision geometry has additional properties attached such as "is walkable", "is climbable", "surface roughness/friction value", etc. The same 'simpler' collision geometry can be used for other purposes too, such as AI pathfinding and 3D audio occlusion.

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not sure if this is specifically a directx question.

Yeah, even though you could use some D3DX maths helper data types and functions to implement it - it's really more of a game programming question.