OpenGL:3D坐標(biāo)到屏幕坐標(biāo)的轉(zhuǎn)換邏輯

遇到需要將3D坐標(biāo)轉(zhuǎn)換到屏幕坐標(biāo)的問(wèn)題，在網(wǎng)上很多朋友也在尋找答案，下面是glu中g(shù)luProject函數(shù)的實(shí)現(xiàn)。
    矩陣按行優(yōu)先存儲(chǔ)
    GLint gluProject(GLdouble objx, GLdouble objy, GLdouble objz,
    const GLdouble model[16], const GLdouble proj[16],
    const GLint viewport[4],
    GLdouble * winx, GLdouble * winy, GLdouble * winz)
    {
    /* matrice de transformation */
    GLdouble in[4], out[4];
    /* initilise la matrice et le vecteur a transformer */
    in[0] = objx;
    in[1] = objy;
    in[2] = objz;
    in[3] = 1.0;
    transform_point(out, model, in);
    transform_point(in, proj, out);
    /* d’ou le resultat normalise entre -1 et 1 */
    if (in[3] == 0.0)
    return GL_FALSE;
    in[0] /= in[3];
    in[1] /= in[3];
    in[2] /= in[3];
    /* en coordonnees ecran */
    *winx = viewport[0] + (1 + in[0]) * viewport[2] / 2;
    *winy = viewport[1] + (1 + in[1]) * viewport[3] / 2;
    /* entre 0 et 1 suivant z */
    *winz = (1 + in[2]) / 2;
    return GL_TRUE;
    }
    /*
    * Transform a point (column vector) by a 4x4 matrix. I.e. out = m * in
    * Input: m - the 4x4 matrix
    * in - the 4x1 vector
    * Output: out - the resulting 4x1 vector.
    */
    static void
    transform_point(GLdouble out[4], const GLdouble m[16], const GLdouble in[4])
    {
    #define M(row,col) m[col*4+row]
    out[0] =
    M(0, 0) * in[0] + M(0, 1) * in[1] + M(0, 2) * in[2] + M(0, 3) * in[3];
    out[1] =
    M(1, 0) * in[0] + M(1, 1) * in[1] + M(1, 2) * in[2] + M(1, 3) * in[3];
    out[2] =
    M(2, 0) * in[0] + M(2, 1) * in[1] + M(2, 2) * in[2] + M(2, 3) * in[3];
    out[3] =
    M(3, 0) * in[0] + M(3, 1) * in[1] + M(3, 2) * in[2] + M(3, 3) * in[3];
    #undef M
    }