v0.92.1 On Solid Ground

A patch for v0.92.0's terrain collision. It said the ground matched the picture. It did not yet — and on a scaled-up terrain the gap was over a metre.

What was wrong

v0.92.0 measured collision against the triangles you see, but decided which side of them you were on by asking the underlying field. Those two surfaces disagree by a fraction of a voxel, and the side is what decides where a body comes to rest — so a character still settled on the field, exactly as before, and the triangles only changed how far away it thought the ground was.

A fraction of a voxel is small until the voxel is not. On a terrain built at a 1.5-unit voxel and scaled up five times, one voxel is 7.5 units across, and the measured gap between where you stood and where the ground was drawn reached 1.15 units — a knight hovering a shin's height over flat ground, and up to his ankles in a slope a few steps away. Both directions on the same hill, and worse the bigger the terrain.

What changed

Collision now decides the side from the drawn surface itself, using the same normals the picture is lit with. On the same terrain the gap is 0.005 units.

Raycasts land on the drawn ground too, which is what a character controller's ground check actually uses: a ray cast at a scaled, rotated terrain stops on the triangles you see, not a voxel above or below them. Digging and sculpting are unaffected, and the cost is unchanged from v0.92.0.

Upgrading

Nothing to change. If a character or a prop was tuned to sit right on v0.92.0's ground, it may now sit a little higher or lower — that difference is the correction, and it is the same everywhere rather than varying from place to place.