Search code examples
cmathmatrixprojection

Why does my parallel projection appear inverted?

I have the following parallel projection (Row major):

enter image description here

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

EDIT correct MATRIX:Matrix

Where a is z rotation,b is y rotation and g is x rotation and s scales my wireframe height.

And it is giving me the following output:

enter image description here

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

enter image description here

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?

Solution

  • 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