After doing some more digging I happened upon this post http://xboxforums.create.msdn.com/forums/t/83491.aspx wherein the user ‘Wipeless XNA’ runs into what appears to be the same issue as myself. He later points out his findings, “However, say your box has no rotation or only rotates about the x-axis [the separation plane check] automatically becomes 0 and returns Disjoint”. In his followup post, he suggests an additional condition before the set of tests on each axis, which skips over those checks if the second box does not contain any nonzero values on the axis in question. I implemented his suggestion, and it appears to have solved the problem for myself as well! More rigorous testing will need to be done, but in the mean time I am marking this thread as solved. In case the aforementioned link expires, I will post the solution code below, which begins on line 576 of BoundingOrientedBox.cs:
if (bX.X != 0 && bY.X != 0 && bZ.X != 0)
{
// a.X ^ b.X = (1,0,0) ^ bX
axis = new Vector3(0, -bX.Z, bX.Y);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Y * axis.Y) + Math.Abs(hA.Z * axis.Z) + Math.Abs(Vector3.Dot(axis, hy_B)) + Math.Abs(Vector3.Dot(axis, hz_B)))
return ContainmentType.Disjoint;
// a.X ^ b.Y = (1,0,0) ^ bY
axis = new Vector3(0, -bY.Z, bY.Y);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Y * axis.Y) + Math.Abs(hA.Z * axis.Z) + Math.Abs(Vector3.Dot(axis, hz_B)) + Math.Abs(Vector3.Dot(axis, hx_B)))
return ContainmentType.Disjoint;
// a.X ^ b.Z = (1,0,0) ^ bZ
axis = new Vector3(0, -bZ.Z, bZ.Y);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Y * axis.Y) + Math.Abs(hA.Z * axis.Z) + Math.Abs(Vector3.Dot(axis, hx_B)) + Math.Abs(Vector3.Dot(axis, hy_B)))
return ContainmentType.Disjoint;
}
if (bX.Y != 0 && bY.Y != 0 && bZ.Y != 0)
{
// a.Y ^ b.X = (0,1,0) ^ bX
axis = new Vector3(bX.Z, 0, -bX.X);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Z * axis.Z) + Math.Abs(hA.X * axis.X) + Math.Abs(Vector3.Dot(axis, hy_B)) + Math.Abs(Vector3.Dot(axis, hz_B)))
return ContainmentType.Disjoint;
// a.Y ^ b.Y = (0,1,0) ^ bY
axis = new Vector3(bY.Z, 0, -bY.X);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Z * axis.Z) + Math.Abs(hA.X * axis.X) + Math.Abs(Vector3.Dot(axis, hz_B)) + Math.Abs(Vector3.Dot(axis, hx_B)))
return ContainmentType.Disjoint;
// a.Y ^ b.Z = (0,1,0) ^ bZ
axis = new Vector3(bZ.Z, 0, -bZ.X);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.Z * axis.Z) + Math.Abs(hA.X * axis.X) + Math.Abs(Vector3.Dot(axis, hx_B)) + Math.Abs(Vector3.Dot(axis, hy_B)))
return ContainmentType.Disjoint;
}
if (bX.Z != 0 && bY.Z != 0 && bZ.Z != 0)
{
// a.Z ^ b.X = (0,0,1) ^ bX
axis = new Vector3(-bX.Y, bX.X, 0);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.X * axis.X) + Math.Abs(hA.Y * axis.Y) + Math.Abs(Vector3.Dot(axis, hy_B)) + Math.Abs(Vector3.Dot(axis, hz_B)))
return ContainmentType.Disjoint;
// a.Z ^ b.Y = (0,0,1) ^ bY
axis = new Vector3(-bY.Y, bY.X, 0);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.X * axis.X) + Math.Abs(hA.Y * axis.Y) + Math.Abs(Vector3.Dot(axis, hz_B)) + Math.Abs(Vector3.Dot(axis, hx_B)))
return ContainmentType.Disjoint;
// a.Z ^ b.Z = (0,0,1) ^ bZ
axis = new Vector3(-bZ.Y, bZ.X, 0);
if (Math.Abs(Vector3.Dot(mB_T, axis)) >= Math.Abs(hA.X * axis.X) + Math.Abs(hA.Y * axis.Y) + Math.Abs(Vector3.Dot(axis, hx_B)) + Math.Abs(Vector3.Dot(axis, hy_B)))
return ContainmentType.Disjoint;
}