gistfile1.c

typedef struct {float x, y;} vec;

vec v(float x, float y){
    vec a = {x, y}; // shorthand for declaration
    return a;
}

float dot(vec a, vec b){
    return a.x*b.x+a.y*b.y;
}

#include <math.h>
vec normalize(vec v){
    float mag = sqrt(v.x*v.x + v.y*v.y);
    vec b = {v.x/mag, v.y/mag}; // vector b is only of distance 1 from the origin
    return b;
}

vec perp(vec v){
    vec b = {v.y, -v.x};
    return b;
}

typedef struct {vec p0, p1, dir;} seg;

seg segment(vec p0, vec p1){
    vec dir = {p1.x-p0.x, p1.y-p0.y};
    seg s = {p0, p1, dir};
    return s;
}

typedef struct {int n; vec *vertices; seg *edges;} polygon; // Assumption: Simply connected => chain vertices together

polygon new_polygon(int nvertices, vec *vertices){
    seg *edges = (seg*)malloc(sizeof(seg)*(nvertices));
    int i;
    for (i = 0; i < nvertices-1; i++){
        vec dir = {vertices[i+1].x-vertices[i].x, vertices[i+1].y-vertices[i].y};seg cur = {vertices[i], vertices[i+1], dir}; // We can also use the segment method here, but this is more explicit
        edges[i] = cur;
    }
    vec dir = {vertices[0].x-vertices[nvertices-1].x, vertices[0].y-vertices[nvertices-1].y};seg cur = {vertices[nvertices-1], vertices[0], dir};
    edges[nvertices-1] = cur; // The last edge is between the first vertex and the last vertex
    polygon shape = {nvertices, vertices, edges};
    return shape;
}

polygon Polygon(int nvertices, ...){
    va_list args;
    va_start(args, nvertices);
    vec *vertices = (vec*)malloc(sizeof(vec)*nvertices);
    int i;
    for (i = 0; i < nvertices; i++){
        vertices[i] = va_arg(args, vec);
    }
    va_end(args);
    return new_polygon(nvertices, vertices);
}