computational-geometry-in-c/src/vertex.c

#include "vertex.h"
#include "math.h"

struct Vertex *new_vertex(int number, int x, int y)
{
    struct Vertex *newv = (struct Vertex *)malloc(sizeof(struct Vertex));

    if (newv == NULL) {
        printf("Out of memory");
        exit(EXIT_FAILURE);
    }

    newv->number         = number;
    newv->coordinates[0] = x;
    newv->coordinates[1] = y;
    newv->ear            = false;

    return newv;
}

void add_vertex(struct Vertex **head, struct Vertex **parent,
                struct Vertex **child)
{
    (*parent)->next = *child;
    (*child)->prev  = *parent;
    (*child)->next  = *head;
    (*head)->prev   = *child;
};

void free_vertex(struct Vertex *vertex)
{
    if (vertex != NULL) {
        free(vertex);
    }
}

void free_polygon(struct Vertex **head)
{
    if(head == NULL) {
        return;
    }

    while(*head != NULL) {
        struct Vertex **temp = head;
        (*head) = (*head)->next;
        free(*temp);
        *temp = NULL;
    }
}

void print_vertex(const struct Vertex *vertex)
{
    printf("VERTEX {number: %d x: %d y: %d ear: %d}\n", vertex->number,
           vertex->coordinates[X], vertex->coordinates[Y], vertex->ear);
}

void print_polygon(const struct Vertex *head) {
    const struct Vertex *v = head->next;

    printf("-------");
    while(v != head) {
        print_vertex(v);
        v = v->next;
    }
}

void init_ear(struct Vertex *head)
{
    // 3 consecutive vertices
    struct Vertex *v0;
    struct Vertex *v1;
    struct Vertex *v2;

    // Initialize v1->ear for all vertices
    v1 = head;

    do {
        v2 = v1->next;
        v0 = v1->prev;

        // If v0v2 is a diagonal, v1 is an ear by definition.
        v1->ear = diagonal(head, v0, v2);

        // Move one point over and run it again.
        v1 = v1->next;
    } while (v1 != head);
}


int vertex_count(const struct Vertex *head)
{
    int sum = 1;
    const struct Vertex *v = head->next;

    while(v != head) {
        sum++;
        v = v->next;
    }

    return sum;
}