Unwanted Bounding Box Padding.

[reepblue]

I brought this up in the discord and now I'm posting it here. It seems that models that have a collision mesh get additional padding on the 2D grid view. This can make it hard to scale certain models like pipes.

No collision box

After adding a box collision shape.

[Josh]

Strange. I tried it with the glTF fox and saw no problem, but this model does show the issue.

models.zip

[Josh]

It appears that NewtonCollisionCalculateAABB is calculating extra padding around box colliders. Probably around all of them, judging by this code.

void dgCollisionInstance::CalcAABB (const dgMatrix& matrix, dgVector& p0, dgVector& p1) const
{
	switch (m_scaleType)
	{
		case m_unit:
		{
			m_childShape->CalcAABB (matrix, p0, p1);
			p0 -= m_padding;
			p1 += m_padding;
			break;
		}

		case m_uniform:
		case m_nonUniform:
		{
			dgMatrix matrix1 (matrix);
			matrix1[0] = matrix1[0].Scale(m_scale.m_x);
			matrix1[1] = matrix1[1].Scale(m_scale.m_y);
			matrix1[2] = matrix1[2].Scale(m_scale.m_z);
			m_childShape->CalcAABB (matrix1, p0, p1);
			p0 -= m_padding;
			p1 += m_padding;
			break;
		}

		case m_global:
		default:
		{
			dgMatrix matrix1 (matrix);
			matrix1[0] = matrix1[0].Scale(m_scale.m_x);
			matrix1[1] = matrix1[1].Scale(m_scale.m_y);
			matrix1[2] = matrix1[2].Scale(m_scale.m_z);
			m_childShape->CalcAABB (m_aligmentMatrix * matrix1, p0, p1);
			p0 -= m_padding;
			p1 += m_padding;
			break;
		}
	}

	dgAssert (p0.m_w == dgFloat32 (0.0f));
	dgAssert (p1.m_w == dgFloat32 (0.0f));
}

 

[Josh]

Here is the value...

#define DG_MAX_COLLISION_AABB_PADDING		dgFloat32 (1.0f / 16.0f)

 

[Josh]

I just reduced the resulting AABB by the value above, and it seems to work correctly.

NewtonCollisionCalculateAABB(col, &identity.i.x, &bounds.min.x, &bounds.max.x);
const float DG_MAX_COLLISION_AABB_PADDING = dgFloat32(1.0f / 16.0f);
bounds.min += DG_MAX_COLLISION_AABB_PADDING;
bounds.max -= DG_MAX_COLLISION_AABB_PADDING;
bounds.Update();