c# - 3D Graphics - Matrix math is not working -

i'm new 3d graphics, expect have done fundamentally wrong. have built 4 matrixes handle objects in 3d space, scaling matrix, translation matrix, perspective matrix , rotation matrix.

the rotation , scaling matrix work fine, perspective , translation matrixes not behave expected, understand translation , perspective matrixes like:

translation      perspective  [1, 0, 0, x]    [1, 0,  0 , 0] [0, 1, 0, y]    [0, 1,  0 , 1] [0, 0, 1, z]    [0, 0,  1 , 0] [0, 0, 0, 1]    [0, 0, 1/d, 1] 

to understand how works behind scenes writing own math lib - create matrixes defined above have following methods:

public static asmatrix4 createperspectivematrix(double focallength) {     // create matrix identity matrix     var m = new asmatrix4();      // set perspective matrix      m.matrix[3].points[2] = 1 / focallength;     m.matrix[1].points[3] = 1;      return m; }  public static asmatrix4 createtranslationmatrix(double x, double y, double z) {     // reset identity matrix     var m = new asmatrix4();      // set translation matrix     m.matrix[0].points[3] = x;     m.matrix[1].points[3] = y;     m.matrix[2].points[3] = z;     return m; } 

nothing complicated, when multiply matrixes together, nothing happens - can rotate axis, cannot translate. note above new asmatrix4() initialises new 4x4 matrix identity matrix.

to multiply matrixes following:

m_scaling = asmatrix4.createscalingmatrix(s, s, s); m_translation = asmatrix4.createtranslationmatrix(tx, ty, tz); m_perspective = asmatrix4.createperspectivematrix(f); m_rotation = asmatrix4.rotatebydegrees(rx, ry, rz);  var transformationmatrix = m_scaling*m_translation*m_perspective*m_rotation; 

i wrote operator overload handle multiplying matrixes together:

public static asmatrix4 operator *(asmatrix4 ma, asmatrix4 mb) {     //  creates new identity matrix     var m = new asmatrix4();      // multiply 2 matrixes , return output matrix     (var = 0; < 4; i++)     {         (var j = 0; j < 4; j++)         {             m.matrix[i].points[j] =                 (mb.matrix[i].points[0]*ma.matrix[0].points[j]) +                 (mb.matrix[i].points[1]*ma.matrix[1].points[j]) +                 (mb.matrix[i].points[2]*ma.matrix[2].points[j]) +                 (mb.matrix[i].points[3]*ma.matrix[3].points[j])         }     }     return m;  } 

finally transform mesh, have array of faces, draw 2d rendering context, method below transforms each face transformation matrix defined above.

private void transformmesh() {     var transformationmatrix = m_scaling*m_translation*m_perspective*m_rotation;     (var = 0; < m_numfaces; i++)     {              m_meshdata[i] = m_meshdata[i].transformface(transformationmatrix);     } } 

the transformface method looks described below:

public asface transformface(asmatrix4 matrix) {     var transformedface = new asface();      (var = 0; < 3; i++)     {         transformedface.m_points[i] = m_points[i].transformvector(matrix);         transformedface.m_points[i] = transformedface.m_points[i].rescale();     }      return transformedface;  } 

this first method in loop transforms homogenous point input matrix, , rescale method called normalise vector.

i'm confused have done wrong? thinking order of operations on multiplying matrixes wrong not sure, suggestions appreciated.

i see 2 problems in posted code. first, createperspectivematrix method not set (1, 3) element 1; either method or initial definition of perspective matrix wrong. (or both!) second, in multiplication code seem multiplying sub-matrix of first 3 rows , columns. since these sub-matrices unit matrices, it's not surprising nothing happens.