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 "simple.h"
#include <stdio.h>
#include <stdlib.h>
#include <cgraph/alloc.h>
#include <cgraph/exit.h>
 
static int gt(const void *a, const void *b);
 
void find_ints(struct vertex vertex_list[],
        struct data *input,
        struct intersection ilist[])
{
    int j, k;
    struct active_edge_list all;
    struct active_edge *tempa;
    struct vertex *pt1, *pt2, *templ;
 
    input->ninters = 0;
    all.first = all.final = NULL;
    all.number = 0;
 
    struct vertex **pvertex = gv_calloc(input->nvertices, sizeof(struct vertex*));
 
    for (size_t i = 0; i < input->nvertices; i++)
        pvertex[i] = vertex_list + i;
 
/* sort vertices by x coordinate        */
    qsort(pvertex, input->nvertices, sizeof(struct vertex *), gt);
 
/* walk through the vertices in order of increasing x coordinate        */
    for (size_t i = 0; i < input->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 (tempa = all.first, j = 0; j < all.number;
                     j++, tempa = tempa->next)
                    find_intersection(tempa->name, templ, ilist, input);        /* test */
 
                struct active_edge *new = gv_alloc(sizeof(struct active_edge));
                if (all.number == 0) {
                    all.first = new;
                    new->last = NULL;
                } /* insert */
                else {
                    all.final->next = new;
                    new->last = all.final;
                }
 
                new->name = templ;
                new->next = NULL;
                templ->active = new;
                all.final = new;
                all.number++;
 
                break;          /* end of case -1       */
 
            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);
                }
                if (all.number == 1)
                    all.final = all.first = NULL;       /* delete the line */
                else if (tempa == all.first) {
                    all.first = all.first->next;
                    all.first->last = NULL;
                } else if (tempa == all.final) {
                    all.final = all.final->last;
                    all.final->next = NULL;
                } else {
                    tempa->last->next = tempa->next;
                    tempa->next->last = tempa->last;
                }
                free(tempa);
                all.number--;
                templ->active = NULL;
                break;          /* end of case 1        */
 
            default:
                break;
            }                   /* end switch   */
 
            pt2 = after(pvertex[i]);
            templ = pvertex[i]; /*second neighbor */
        }                       /* end k for loop       */
    }                           /* end i for loop       */
    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;
}