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tessmono.c
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1/*
2 * SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
3 * Copyright (C) 1991-2000 Silicon Graphics, Inc. All Rights Reserved.
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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 */
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 */
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 */
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 ) {
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 */
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}
unsigned char GLboolean
Definition: GL_glu.h:267
#define f(i)
Definition: RSha256.hxx:104
#define e(i)
Definition: RSha256.hxx:103
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void value
#define VertLeq(u, v)
Definition: geom.h:50
#define EdgeGoesRight(e)
Definition: geom.h:66
#define EdgeGoesLeft(e)
Definition: geom.h:65
#define EdgeSign(u, v, w)
Definition: geom.h:55
void __gl_meshZapFace(GLUface *fZap)
Definition: mesh.c:550
GLUhalfEdge * __gl_meshConnect(GLUhalfEdge *eOrg, GLUhalfEdge *eDst)
Definition: mesh.c:503
int __gl_meshDelete(GLUhalfEdge *eDel)
Definition: mesh.c:379
Definition: mesh.h:126
GLUhalfEdge * anEdge
Definition: mesh.h:129
GLUhalfEdge * Lnext
Definition: mesh.h:142
GLUvertex * Org
Definition: mesh.h:143
GLUhalfEdge * Sym
Definition: mesh.h:140
Definition: mesh.h:168
Definition: triangle.c:632
int __gl_meshTessellateMonoRegion(GLUface *face)
Definition: tessmono.c:72
int __gl_meshSetWindingNumber(GLUmesh *mesh, int value, GLboolean keepOnlyBoundary)
Definition: tessmono.c:179
void __gl_meshDiscardExterior(GLUmesh *mesh)
Definition: tessmono.c:155
int __gl_meshTessellateInterior(GLUmesh *mesh)
Definition: tessmono.c:133