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/**
* @file
* @brief trapezoid elements and utilities for partition.c
*
* See [Fast polygon triangulation based on Seidel's algorithm](http://gamma.cs.unc.edu/SEIDEL/)
*
*/
/*************************************************************************
* 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
*************************************************************************/
#pragma once
#include <math.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <util/list.h>
/* Segment attributes */
typedef struct {
pointf v0, v1; /* two endpoints */
bool is_inserted; /* inserted in trapezoidation yet ? */
size_t root0, root1; ///< root nodes in Q
int next; /* Next logical segment */
int prev; /* Previous segment */
} segment_t;
/* Trapezoid attributes */
typedef struct {
int lseg, rseg; /* two adjoining segments */
pointf hi, lo; /* max/min y-values */
size_t u0, u1;
size_t d0, d1;
size_t sink; ///< pointer to corresponding in Q
size_t usave; ///< I forgot what this means
int uside; ///< I forgot what this means
bool is_valid;
} trap_t;
/// is the given index a reference to an existing trapezoid?
///
/// The indices stored in `trap_t.{u0|u1|d0|d1|usave}` can contain sentinel
/// values that represent an unset or invalid trapezoid. This function can be
/// used to determine the validity of these fields.
static inline bool is_valid_trap(size_t index) {
return index != 0 && index != SIZE_MAX;
}
/// an array of trapezoids
typedef LIST(trap_t) traps_t;
#define C_EPS 1.0e-7 /* tolerance value: Used for making */
/* all decisions about collinearity or */
/* left/right of segment. Decrease */
/* this value if the input points are */
/* spaced very close together */
static inline bool fp_equal(double s, double t) { return fabs(s - t) <= C_EPS; }
/**
* @brief double floating point three-way comparison
*
* Returns -1, 0, or 1 if f1 respectively, less than,
* almost equal with tolerance C_EPS, or greater than f2.
* The purpose of the function is workaround precision issues.
*/
static inline int dfp_cmp(double f1, double f2) {
double d = f1 - f2;
if (d < -C_EPS)
return -1;
if (d > C_EPS)
return 1;
return 0;
}
static inline bool equal_to(pointf v0, pointf v1) {
return fp_equal(v0.y, v1.y) && fp_equal(v0.x, v1.x);
}
static inline bool greater_than(pointf v0, pointf v1) {
return v0.y > v1.y + C_EPS ? true
: (v0.y < v1.y - C_EPS ? false : v0.x > v1.x);
}
extern traps_t construct_trapezoids(int, segment_t*, int*);
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