Bug in mult_matrix_4

[telamonian]

It seems that the mult_matrix_4 function is showing some odd behavior. I defined a 4x4 transformation matrix that should move a shape up by 3 units and then rotate that shape by pi/7 radians about the point (0, 3.5, 0) and about the axis (0,0,1):

tmat = [[ 0.90096887 -0.43388374  0.          0.21694187]
        [ 0.43388374  0.90096887  0.          3.04951557]
        [ 0.          0.          1.          0.        ]
        [ 0.          0.          0.          1.        ]]

I then flattened the matrix in row-major format, as mult_matrix_4 seems to require:

formatted_tmat = [0.9009688679024191, -0.4338837391175581, 0.0, 0.21694186955877903, 0.4338837391175581, 0.9009688679024191, 0.0, 3.0495155660487905, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0]

I then made a box in pyPolyCSG and applied the transformation:

a = csg.box(3.0,1.0,1.0)
b = a.mult_matrix_4(formatted_tmat)

In terms of the first 4 vertices (as returned by b.get_vertices()), I get what seems to be a translation + dilation of my shape:

[0.21694187, 3.04951557, 0]
[1.61819726, 3.04951557, 0]
[1.61819726, 4.38436817, 0]
[0.21694187, 4.38436817, 0] 

I was expecting to get a translation + rotation of the box, as I do when I multiply the vertex coordinates by the transformation matrix by hand:

[0.216942, 3.04952, 0.]
[2.91985, 4.35117, 0.]
[2.48596, 5.25214, 0]
[-0.216942, 3.95048, 0]

Do you know what's causing the discrepancy, and do you know how I can fix it?

[telamonian]

There seems to have been an error in polyhedron polyhedron_multmatrix4::operator()( const polyhedron &in ), the function that handled the matrix multiplication for mult_matrix_4. One of the indices in the matrix multiplication routine itself was wrong. I fixed it, and also simplified the function somewhat.