space_game/vect.c

#include "vect.h"

double vect_dot(Vect V, Vect B) {
    return V.x * B.x + V.y * B.y;
}

double vect_mag(Vect v) {
    double mag = sqrt((v.x * v.x) + (v.y * v.y));
    return mag;
}

Vect vect_scalar(Vect V, double s) {
    Vect ret;
    ret.x = V.x * s;
    ret.y = V.y * s;
    return ret;
}


Vect vect_add(Vect v1, Vect v2) {
    Vect res;
    res.x = v1.x + v2.x;
    res.y = v1.y + v2.y;
    return res;
}

// project one onto two
Vect project_vect(Vect one, Vect two) {
    // $$ a \cdot \frac {|b|} {b} $$
    Vect unittwo;
    unittwo.x = two.x / vect_mag(two);
    unittwo.y = two.y / vect_mag(two);

    Vect proj;
    proj.x = unittwo.x * one.x;
    proj.y = unittwo.y * one.y;

    return proj;
}

// project V onto P
double vect_scalar_projection(Vect V, Vect P) {
    double angle = vect_dir(V) - vect_dir(P);
    return cos(angle) * vect_mag(V);
}

double vect_dir(Vect V) {
    return atan2(V.y, V.x);
}