src/glu/sgi/libtess/tessmono.c

   1 /*
   2 ** License Applicability. Except to the extent portions of this file are
   3 ** made subject to an alternative license as permitted in the SGI Free
   4 ** Software License B, Version 1.1 (the "License"), the contents of this
   5 ** file are subject only to the provisions of the License. You may not use
   6 ** this file except in compliance with the License. You may obtain a copy
   7 ** of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
   8 ** Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:
   9 **
  10 ** http://oss.sgi.com/projects/FreeB
  11 **
  12 ** Note that, as provided in the License, the Software is distributed on an
  13 ** "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
  14 ** DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
  15 ** CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
  16 ** PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
  17 **
  18 ** Original Code. The Original Code is: OpenGL Sample Implementation,
  19 ** Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
  20 ** Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
  21 ** Copyright in any portions created by third parties is as indicated
  22 ** elsewhere herein. All Rights Reserved.
  23 **
  24 ** Additional Notice Provisions: The application programming interfaces
  25 ** established by SGI in conjunction with the Original Code are The
  26 ** OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
  27 ** April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
  28 ** 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
  29 ** Window System(R) (Version 1.3), released October 19, 1998. This software
  30 ** was created using the OpenGL(R) version 1.2.1 Sample Implementation
  31 ** published by SGI, but has not been independently verified as being
  32 ** compliant with the OpenGL(R) version 1.2.1 Specification.
  33 **
  34 */
  35 /*
  36 ** Author: Eric Veach, July 1994.
  37 **
  38 */
  39
  40 #include "gluos.h"
  41 #include <stdlib.h>
  42 #include "geom.h"
  43 #include "mesh.h"
  44 #include "tessmono.h"
  45 #include <assert.h>
  46
  47 #define AddWinding(eDst,eSrc)   (eDst->winding += eSrc->winding, \
  48                                  eDst->Sym->winding += eSrc->Sym->winding)
  49
  50 /* __gl_meshTessellateMonoRegion( face ) tessellates a monotone region
  51  * (what else would it do??)  The region must consist of a single
  52  * loop of half-edges (see mesh.h) oriented CCW.  "Monotone" in this
  53  * case means that any vertical line intersects the interior of the
  54  * region in a single interval.
  55  *
  56  * Tessellation consists of adding interior edges (actually pairs of
  57  * half-edges), to split the region into non-overlapping triangles.
  58  *
  59  * The basic idea is explained in Preparata and Shamos (which I don''t
  60  * have handy right now), although their implementation is more
  61  * complicated than this one.  The are two edge chains, an upper chain
  62  * and a lower chain.  We process all vertices from both chains in order,
  63  * from right to left.
  64  *
  65  * The algorithm ensures that the following invariant holds after each
  66  * vertex is processed: the untessellated region consists of two
  67  * chains, where one chain (say the upper) is a single edge, and
  68  * the other chain is concave.  The left vertex of the single edge
  69  * is always to the left of all vertices in the concave chain.
  70  *
  71  * Each step consists of adding the rightmost unprocessed vertex to one
  72  * of the two chains, and forming a fan of triangles from the rightmost
  73  * of two chain endpoints.  Determining whether we can add each triangle
  74  * to the fan is a simple orientation test.  By making the fan as large
  75  * as possible, we restore the invariant (check it yourself).
  76  */
  77 int __gl_meshTessellateMonoRegion( GLUface *face )
  78 {
  79   GLUhalfEdge *up, *lo;
  80
  81   /* All edges are oriented CCW around the boundary of the region.
  82    * First, find the half-edge whose origin vertex is rightmost.
  83    * Since the sweep goes from left to right, face->anEdge should
  84    * be close to the edge we want.
  85    */
  86   up = face->anEdge;
  87   assert( up->Lnext != up && up->Lnext->Lnext != up );
  88
  89   for( ; VertLeq( up->Dst, up->Org ); up = up->Lprev )
  90     ;
  91   for( ; VertLeq( up->Org, up->Dst ); up = up->Lnext )
  92     ;
  93   lo = up->Lprev;
  94
  95   while( up->Lnext != lo ) {
  96     if( VertLeq( up->Dst, lo->Org )) {
  97       /* up->Dst is on the left.  It is safe to form triangles from lo->Org.
  98        * The EdgeGoesLeft test guarantees progress even when some triangles
  99        * are CW, given that the upper and lower chains are truly monotone.
 100        */
 101       while( lo->Lnext != up && (EdgeGoesLeft( lo->Lnext )
 102              || EdgeSign( lo->Org, lo->Dst, lo->Lnext->Dst ) <= 0 )) {
 103         GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
 104         if (tempHalfEdge == NULL) return 0;
 105         lo = tempHalfEdge->Sym;
 106       }
 107       lo = lo->Lprev;
 108     } else {
 109       /* lo->Org is on the left.  We can make CCW triangles from up->Dst. */
 110       while( lo->Lnext != up && (EdgeGoesRight( up->Lprev )
 111              || EdgeSign( up->Dst, up->Org, up->Lprev->Org ) >= 0 )) {
 112         GLUhalfEdge *tempHalfEdge= __gl_meshConnect( up, up->Lprev );
 113         if (tempHalfEdge == NULL) return 0;
 114         up = tempHalfEdge->Sym;
 115       }
 116       up = up->Lnext;
 117     }
 118   }
 119
 120   /* Now lo->Org == up->Dst == the leftmost vertex.  The remaining region
 121    * can be tessellated in a fan from this leftmost vertex.
 122    */
 123   assert( lo->Lnext != up );
 124   while( lo->Lnext->Lnext != up ) {
 125     GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
 126     if (tempHalfEdge == NULL) return 0;
 127     lo = tempHalfEdge->Sym;
 128   }
 129
 130   return 1;
 131 }
 132
 133
 134 /* __gl_meshTessellateInterior( mesh ) tessellates each region of
 135  * the mesh which is marked "inside" the polygon.  Each such region
 136  * must be monotone.
 137  */
 138 int __gl_meshTessellateInterior( GLUmesh *mesh )
 139 {
 140   GLUface *f, *next;
 141
 142   /*LINTED*/
 143   for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
 144     /* Make sure we don''t try to tessellate the new triangles. */
 145     next = f->next;
 146     if( f->inside ) {
 147       if ( !__gl_meshTessellateMonoRegion( f ) ) return 0;
 148     }
 149   }
 150
 151   return 1;
 152 }
 153
 154
 155 /* __gl_meshDiscardExterior( mesh ) zaps (ie. sets to NULL) all faces
 156  * which are not marked "inside" the polygon.  Since further mesh operations
 157  * on NULL faces are not allowed, the main purpose is to clean up the
 158  * mesh so that exterior loops are not represented in the data structure.
 159  */
 160 void __gl_meshDiscardExterior( GLUmesh *mesh )
 161 {
 162   GLUface *f, *next;
 163
 164   /*LINTED*/
 165   for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
 166     /* Since f will be destroyed, save its next pointer. */
 167     next = f->next;
 168     if( ! f->inside ) {
 169       __gl_meshZapFace( f );
 170     }
 171   }
 172 }
 173
 174 #define MARKED_FOR_DELETION     0x7fffffff
 175
 176 /* __gl_meshSetWindingNumber( mesh, value, keepOnlyBoundary ) resets the
 177  * winding numbers on all edges so that regions marked "inside" the
 178  * polygon have a winding number of "value", and regions outside
 179  * have a winding number of 0.
 180  *
 181  * If keepOnlyBoundary is TRUE, it also deletes all edges which do not
 182  * separate an interior region from an exterior one.
 183  */
 184 int __gl_meshSetWindingNumber( GLUmesh *mesh, int value,
 185                                 GLboolean keepOnlyBoundary )
 186 {
 187   GLUhalfEdge *e, *eNext;
 188
 189   for( e = mesh->eHead.next; e != &mesh->eHead; e = eNext ) {
 190     eNext = e->next;
 191     if( e->Rface->inside != e->Lface->inside ) {
 192
 193       /* This is a boundary edge (one side is interior, one is exterior). */
 194       e->winding = (e->Lface->inside) ? value : -value;
 195     } else {
 196
 197       /* Both regions are interior, or both are exterior. */
 198       if( ! keepOnlyBoundary ) {
 199         e->winding = 0;
 200       } else {
 201         if ( !__gl_meshDelete( e ) ) return 0;
 202       }
 203     }
 204   }
 205   return 1;
 206 }