Fix setMass; correct terrain sampling

[jmiskovic]

For terrain sampling fix, this is the before and after.

world = lovr.physics.newWorld()
collider = world:newTerrainCollider(4, function(x, z) return 1 end, 128)

function lovr.draw(pass)
  pass:setProjection(1, mat4():orthographic(-3, 3, 3, -3, 0.01, 100))
  pass:plane(0, 0, 0,  4, 4, -math.pi/2, 1,0,0, 'line')
  for x = -5, 5, 0.2 do
    for z = -5, 5, 0.2 do
      o = vec3(x,  100, z)
      t = vec3(x, -100, z)
      world:raycast(o, t,
        function(shape, x, y, z, nx, ny, nz)
         pass:sphere(x, y, z, 0.05)
         pass:line(x, y, z, x+nx, y+ny, z+nz)
        end)
    end
  end
end

[bjornbytes]

Couldn't this also be / (n - 1) instead of / (n + 1)? That way the callback gives you this when samples = 2

-2.00, -2.00,
2.00, -2.00,
-2.00, 2.00
2.00, 2.00

instead of this

-2.00, -2.00
-.667, -2.00
-2.00, -.667
-.667, -.667

Also for some reason Jolt crashes when samples == 2, but that's a separate thing.

[jmiskovic]

Yup, fixed. The screenshot was with n-1 but I submitted wrong version.

[bjornbytes]

Cool, looks good!