/* vector2.c: Package for manipulating 2-dimensional vectors */

#include "vector2.h" /* For the vector structure declaration */
#include <math.h>    /* For sqrt, sin, cos & atan2 functions */

vector2 v2Add(vector2 a, vector2 b) {    /* Sum of 2 vectors */
    vector2 c;
    c.x = a.x + b.x;    /* Adds the x components */
    c.y = a.y + b.y;    /* Adds the y components */
    return c;
}

vector2 v2Sub(vector2 a, vector2 b) {    /* Difference */
    vector2 c;
    c.x = a.x - b.x;    /* Subtracts the x components */
    c.y = a.y - b.y;    /* Subtracts the y components */
    return c;
}

vector2 v2Neg(vector2 a) {               /* Negative of vector */
    a.x = -a.x;  /* Negate x; this does not alter the actual parameter a */
    a.y = -a.y;  /* Negate y; this does not alter the actual parameter a */
    return a;
}

vector2 sv2Mul(float f, vector2 v) {     /* Multiply by a scalar */
    v.x *= f;   /* Multiply x by scalar; does not alter actual parameter */
    v.y *= f;   /* Multiply y by scalar; does not alter actual parameter */
    return v;
}

float v2Len(vector2 v) {                 /* Length of vector */
    return sqrt(v.x * v.x  +  v.y * v.y);  /* Pythagoras' rule */
}
/* (A better version of the function v2Len is given in chapter 16.) */

float v2Arg(vector2 v) {                 /* Angle of vector with x axis */
    return atan2(v.y, v.x);  /* Note: meaningless if v.y & v.x both zero */
}

vector2 v2Polar(float len, float angle) {
    /* Compute vector from its length and direction */
    vector2 v;
    v.x = len * cos(angle);
    v.y = len * sin(angle);
    return v;
}