Projective Shadows in OpenGL

shadow-matrix.c

void setShadowMatrix(GLfloat *destMat, float *lightPos, double *plane)
{
    GLfloat dot;

    // dot product of plane and light position
    dot = plane[0] * lightPos[0] + plane[1] * lightPos[1] + plane[2] * lightPos[2];

    // first column
    destMat[0]  = dot  - plane[0] * lightPos[0];
    destMat[4]  = 0.0f - lightPos[0] * plane[1];
    destMat[8]  = 0.0f - lightPos[0] * plane[2];
    destMat[12] = 0.0f - lightPos[0] * plane[3];

    // second column
    destMat[1]  = 0.0f - lightPos[1] * plane[0];
    destMat[5]  = dot  - lightPos[1] * plane[1];
    destMat[9]  = 0.0f - lightPos[1] * plane[2];
    destMat[13] = 0.0f - lightPos[1] * plane[3];

    // third column
    destMat[2]  = 0.0f - lightPos[2] * plane[0];
    destMat[6]  = 0.0f - lightPos[2] * plane[1];
    destMat[10] = dot  - lightPos[2] * plane[2];
    destMat[14] = 0.0f - lightPos[2] * plane[3];

    // fourth column
    destMat[3]  = 0.0f - lightPos[3] * plane[0];
    destMat[7]  = 0.0f - lightPos[3] * plane[1];
    destMat[11] = 0.0f - lightPos[3] * plane[2];
    destMat[15] = dot  - lightPos[3] * plane[3];
}