1/*
2 * SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
3 * Copyright (C) 1991-2000 Silicon Graphics, Inc. All Rights Reserved.
4 *
5 * Permission is hereby granted, free of charge, to any person obtaining a
6 * copy of this software and associated documentation files (the "Software"),
7 * to deal in the Software without restriction, including without limitation
8 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9 * and/or sell copies of the Software, and to permit persons to whom the
10 * Software is furnished to do so, subject to the following conditions:
11 *
12 * The above copyright notice including the dates of first publication and
13 * either this permission notice or a reference to
14 * http://oss.sgi.com/projects/FreeB/
15 * shall be included in all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
18 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
20 * SILICON GRAPHICS, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
21 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
22 * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
23 * SOFTWARE.
24 *
25 * Except as contained in this notice, the name of Silicon Graphics, Inc.
26 * shall not be used in advertising or otherwise to promote the sale, use or
27 * other dealings in this Software without prior written authorization from
28 * Silicon Graphics, Inc.
29 */
30/*
31** Author: Eric Veach, July 1994.
32**
33*/
34
35#include "gluos.h"
36#include <stdlib.h>
37#include "geom.h"
38#include "mesh.h"
39#include "tessmono.h"
40#include <assert.h>
41
42#define AddWinding(eDst,eSrc)	(eDst->winding += eSrc->winding, \
43				 eDst->Sym->winding += eSrc->Sym->winding)
44
45/* __gl_meshTessellateMonoRegion( face ) tessellates a monotone region
46 * (what else would it do??)  The region must consist of a single
47 * loop of half-edges (see mesh.h) oriented CCW.  "Monotone" in this
48 * case means that any vertical line intersects the interior of the
49 * region in a single interval.
50 *
51 * Tessellation consists of adding interior edges (actually pairs of
52 * half-edges), to split the region into non-overlapping triangles.
53 *
54 * The basic idea is explained in Preparata and Shamos (which I don''t
55 * have handy right now), although their implementation is more
56 * complicated than this one.  The are two edge chains, an upper chain
57 * and a lower chain.  We process all vertices from both chains in order,
58 * from right to left.
59 *
60 * The algorithm ensures that the following invariant holds after each
61 * vertex is processed: the untessellated region consists of two
62 * chains, where one chain (say the upper) is a single edge, and
63 * the other chain is concave.  The left vertex of the single edge
64 * is always to the left of all vertices in the concave chain.
65 *
66 * Each step consists of adding the rightmost unprocessed vertex to one
67 * of the two chains, and forming a fan of triangles from the rightmost
68 * of two chain endpoints.  Determining whether we can add each triangle
69 * to the fan is a simple orientation test.  By making the fan as large
70 * as possible, we restore the invariant (check it yourself).
71 */
72int __gl_meshTessellateMonoRegion( GLUface *face )
73{
74  GLUhalfEdge *up, *lo;
75
76  /* All edges are oriented CCW around the boundary of the region.
77   * First, find the half-edge whose origin vertex is rightmost.
78   * Since the sweep goes from left to right, face->anEdge should
79   * be close to the edge we want.
80   */
81  up = face->anEdge;
82  assert( up->Lnext != up && up->Lnext->Lnext != up );
83
84  for( ; VertLeq( up->Dst, up->Org ); up = up->Lprev )
85    ;
86  for( ; VertLeq( up->Org, up->Dst ); up = up->Lnext )
87    ;
88  lo = up->Lprev;
89
90  while( up->Lnext != lo ) {
91    if( VertLeq( up->Dst, lo->Org )) {
92      /* up->Dst is on the left.  It is safe to form triangles from lo->Org.
93       * The EdgeGoesLeft test guarantees progress even when some triangles
94       * are CW, given that the upper and lower chains are truly monotone.
95       */
96      while( lo->Lnext != up && (EdgeGoesLeft( lo->Lnext )
97	     || EdgeSign( lo->Org, lo->Dst, lo->Lnext->Dst ) <= 0 )) {
98	GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
99	if (tempHalfEdge == NULL) return 0;
100	lo = tempHalfEdge->Sym;
101      }
102      lo = lo->Lprev;
103    } else {
104      /* lo->Org is on the left.  We can make CCW triangles from up->Dst. */
105      while( lo->Lnext != up && (EdgeGoesRight( up->Lprev )
106	     || EdgeSign( up->Dst, up->Org, up->Lprev->Org ) >= 0 )) {
107	GLUhalfEdge *tempHalfEdge= __gl_meshConnect( up, up->Lprev );
108	if (tempHalfEdge == NULL) return 0;
109	up = tempHalfEdge->Sym;
110      }
111      up = up->Lnext;
112    }
113  }
114
115  /* Now lo->Org == up->Dst == the leftmost vertex.  The remaining region
116   * can be tessellated in a fan from this leftmost vertex.
117   */
118  assert( lo->Lnext != up );
119  while( lo->Lnext->Lnext != up ) {
120    GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
121    if (tempHalfEdge == NULL) return 0;
122    lo = tempHalfEdge->Sym;
123  }
124
125  return 1;
126}
127
128
129/* __gl_meshTessellateInterior( mesh ) tessellates each region of
130 * the mesh which is marked "inside" the polygon.  Each such region
131 * must be monotone.
132 */
133int __gl_meshTessellateInterior( GLUmesh *mesh )
134{
135  GLUface *f, *next;
136
137  /*LINTED*/
138  for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
139    /* Make sure we don''t try to tessellate the new triangles. */
140    next = f->next;
141    if( f->inside ) {
142      if ( !__gl_meshTessellateMonoRegion( f ) ) return 0;
143    }
144  }
145
146  return 1;
147}
148
149
150/* __gl_meshDiscardExterior( mesh ) zaps (ie. sets to NULL) all faces
151 * which are not marked "inside" the polygon.  Since further mesh operations
152 * on NULL faces are not allowed, the main purpose is to clean up the
153 * mesh so that exterior loops are not represented in the data structure.
154 */
155void __gl_meshDiscardExterior( GLUmesh *mesh )
156{
157  GLUface *f, *next;
158
159  /*LINTED*/
160  for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
161    /* Since f will be destroyed, save its next pointer. */
162    next = f->next;
163    if( ! f->inside ) {
164      __gl_meshZapFace( f );
165    }
166  }
167}
168
169#define MARKED_FOR_DELETION	0x7fffffff
170
171/* __gl_meshSetWindingNumber( mesh, value, keepOnlyBoundary ) resets the
172 * winding numbers on all edges so that regions marked "inside" the
173 * polygon have a winding number of "value", and regions outside
174 * have a winding number of 0.
175 *
176 * If keepOnlyBoundary is TRUE, it also deletes all edges which do not
177 * separate an interior region from an exterior one.
178 */
179int __gl_meshSetWindingNumber( GLUmesh *mesh, int value,
180			        GLboolean keepOnlyBoundary )
181{
182  GLUhalfEdge *e, *eNext;
183
184  for( e = mesh->eHead.next; e != &mesh->eHead; e = eNext ) {
185    eNext = e->next;
186    if( e->Rface->inside != e->Lface->inside ) {
187
188      /* This is a boundary edge (one side is interior, one is exterior). */
189      e->winding = (e->Lface->inside) ? value : -value;
190    } else {
191
192      /* Both regions are interior, or both are exterior. */
193      if( ! keepOnlyBoundary ) {
194	e->winding = 0;
195      } else {
196	if ( !__gl_meshDelete( e ) ) return 0;
197      }
198    }
199  }
200  return 1;
201}
202