find_ints.c

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/*************************************************************************
 * Copyright (c) 2011 AT&T Intellectual Property 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors: Details at https://graphviz.org
 *************************************************************************/
 
#include "config.h"
 
#include "simple.h"
#include <stdio.h>
#include <stdlib.h>
#include <util/alloc.h>
#include <util/exit.h>
#include <util/list.h>
 
static int gt(const void *a, const void *b);
 
void find_ints(struct vertex vertex_list[], size_t nvertices,
               intersections_t *ilist) {
    int k;
    LIST(struct active_edge *) all = {.dtor = LIST_DTOR_FREE};
    struct active_edge *tempa;
    struct vertex *pt1, *pt2, *templ;
 
    struct vertex **pvertex = gv_calloc(nvertices, sizeof(struct vertex*));
 
    for (size_t i = 0; i < nvertices; i++)
        pvertex[i] = vertex_list + i;
 
/* sort vertices by x coordinate        */
    qsort(pvertex, nvertices, sizeof(struct vertex *), gt);
 
/* walk through the vertices in order of increasing x coordinate        */
    for (size_t i = 0; i < nvertices; i++) {
        pt1 = pvertex[i];
        templ = pt2 = prior(pvertex[i]);
        for (k = 0; k < 2; k++) {       /* each vertex has 2 edges */
            switch (gt(&pt1, &pt2)) {
 
            case -1:            /* forward edge, test and insert      */
                for (size_t j = 0; j < LIST_SIZE(&all); ++j) {
                    tempa = LIST_GET(&all, j);
                    find_intersection(tempa->name, templ, ilist); // test
                }
 
                struct active_edge *new = gv_alloc(sizeof(struct active_edge));
                LIST_APPEND(&all, new);
 
                new->name = templ;
                templ->active = new;
                break;
 
            case 1:             /* backward edge, delete        */
 
                if ((tempa = templ->active) == NULL) {
                    fprintf(stderr,
                            "\n***ERROR***\n trying to delete a non line\n");
                    graphviz_exit(1);
                }
                LIST_REMOVE(&all, tempa);
                templ->active = NULL;
                break;
 
            default:
                break;
            }
 
            pt2 = after(pvertex[i]);
            templ = pvertex[i]; /*second neighbor */
        }
    }
    LIST_FREE(&all);
    free(pvertex);
}
 
static int gt(const void *a, const void *b) {
    const struct vertex *const *i = a;
    const struct vertex *const *j = b;
    if ((*i)->pos.x > (*j)->pos.x) {
      return 1;
    }
    if ((*i)->pos.x < (*j)->pos.x) {
      return -1;
    }
    if ((*i)->pos.y > (*j)->pos.y) {
      return 1;
    }
    if ((*i)->pos.y < (*j)->pos.y) {
      return -1;
    }
    return 0;
}