Why does my parallel projection appear inverted?-CodePudding

I have the following parallel projection (Row major):

Before I apply the projection I use the following matrix to apply a transformation on the original points:

EDIT correct MATRIX:

When in reality it should be giving me this (image not centered):

n is 0.1 and f is 100 The origin is in the middle of the wireframe and the 42 wireframe height is in the z direction.

My matrix multiplication:

typedef struct s_point
{
    float   x;
    float   y;
    float   z;
    int     c; //color
}   t_point;


void    multiply_matrix_vector(t_point *i, t_point *o, t_pmatrix *m)
{
    float   w;

    o->x = i->x * m->m[0][0]   i->y * m->m[1][0]   i->z * m->m[2][0]   m->m[3][0];
    o->y = i->x * m->m[0][1]   i->y * m->m[1][1]   i->z * m->m[2][1]   m->m[3][1];
    o->z = i->x * m->m[0][2]   i->y * m->m[1][2]   i->z * m->m[2][2]   m->m[3][2];
    w = i->x * m->m[0][3]   i->y * m->m[1][3]   i->z * m->m[2][3]   m->m[3][3];
    if (w != 0.0f)
    {
        o->x /= w;
        o->y /= w;
        o->z /= w;
    }
    o->c = i->c;
}

What am I doing wrong?

CodePudding user response：

I remembered that I was having a hard time with matrix multiplication before and that probably I might had screwed a sign or a trigonometric function. I double checked everything and but all was ok. Still the result was flipped on the y axis so what I did was this:

Matrix

On the first matrix at [1][1] I just changed the 1 for -1

Matrices are tricky because the multiplication order matters more than one would think