SGI SI GLU library

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+/*
+** License Applicability. Except to the extent portions of this file are
+** made subject to an alternative license as permitted in the SGI Free
+** Software License B, Version 1.1 (the "License"), the contents of this
+** file are subject only to the provisions of the License. You may not use
+** this file except in compliance with the License. You may obtain a copy
+** of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
+** Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:
+** 
+** http://oss.sgi.com/projects/FreeB
+** 
+** Note that, as provided in the License, the Software is distributed on an
+** "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
+** DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
+** CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
+** PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
+** 
+** Original Code. The Original Code is: OpenGL Sample Implementation,
+** Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
+** Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
+** Copyright in any portions created by third parties is as indicated
+** elsewhere herein. All Rights Reserved.
+** 
+** Additional Notice Provisions: The application programming interfaces
+** established by SGI in conjunction with the Original Code are The
+** OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
+** April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
+** 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
+** Window System(R) (Version 1.3), released October 19, 1998. This software
+** was created using the OpenGL(R) version 1.2.1 Sample Implementation
+** published by SGI, but has not been independently verified as being
+** compliant with the OpenGL(R) version 1.2.1 Specification.
+**
+*/
+/*
+** Author: Eric Veach, July 1994.
+**
+** $Date: 2001/03/17 00:25:41 $ $Revision: 1.1 $
+** $Header: /home/krh/git/sync/mesa-cvs-repo/Mesa/src/glu/sgi/libtess/tessmono.c,v 1.1 2001/03/17 00:25:41 brianp Exp $
+*/
+
+#include "gluos.h"
+#include <stdlib.h>
+#include "geom.h"
+#include "mesh.h"
+#include "tessmono.h"
+#include <assert.h>
+
+#define AddWinding(eDst,eSrc)	(eDst->winding += eSrc->winding, \
+				 eDst->Sym->winding += eSrc->Sym->winding)
+
+/* __gl_meshTessellateMonoRegion( face ) tessellates a monotone region
+ * (what else would it do??)  The region must consist of a single
+ * loop of half-edges (see mesh.h) oriented CCW.  "Monotone" in this
+ * case means that any vertical line intersects the interior of the
+ * region in a single interval.  
+ *
+ * Tessellation consists of adding interior edges (actually pairs of
+ * half-edges), to split the region into non-overlapping triangles.
+ *
+ * The basic idea is explained in Preparata and Shamos (which I don''t
+ * have handy right now), although their implementation is more
+ * complicated than this one.  The are two edge chains, an upper chain
+ * and a lower chain.  We process all vertices from both chains in order,
+ * from right to left.
+ *
+ * The algorithm ensures that the following invariant holds after each
+ * vertex is processed: the untessellated region consists of two
+ * chains, where one chain (say the upper) is a single edge, and
+ * the other chain is concave.  The left vertex of the single edge
+ * is always to the left of all vertices in the concave chain.
+ *
+ * Each step consists of adding the rightmost unprocessed vertex to one
+ * of the two chains, and forming a fan of triangles from the rightmost
+ * of two chain endpoints.  Determining whether we can add each triangle
+ * to the fan is a simple orientation test.  By making the fan as large
+ * as possible, we restore the invariant (check it yourself).
+ */
+int __gl_meshTessellateMonoRegion( GLUface *face )
+{
+  GLUhalfEdge *up, *lo;
+
+  /* All edges are oriented CCW around the boundary of the region.
+   * First, find the half-edge whose origin vertex is rightmost.
+   * Since the sweep goes from left to right, face->anEdge should
+   * be close to the edge we want.
+   */
+  up = face->anEdge;
+  assert( up->Lnext != up && up->Lnext->Lnext != up );
+
+  for( ; VertLeq( up->Dst, up->Org ); up = up->Lprev )
+    ;
+  for( ; VertLeq( up->Org, up->Dst ); up = up->Lnext )
+    ;
+  lo = up->Lprev;
+
+  while( up->Lnext != lo ) {
+    if( VertLeq( up->Dst, lo->Org )) {
+      /* up->Dst is on the left.  It is safe to form triangles from lo->Org.
+       * The EdgeGoesLeft test guarantees progress even when some triangles
+       * are CW, given that the upper and lower chains are truly monotone.
+       */
+      while( lo->Lnext != up && (EdgeGoesLeft( lo->Lnext )
+	     || EdgeSign( lo->Org, lo->Dst, lo->Lnext->Dst ) <= 0 )) {
+	GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
+	if (tempHalfEdge == NULL) return 0;
+	lo = tempHalfEdge->Sym;
+      }
+      lo = lo->Lprev;
+    } else {
+      /* lo->Org is on the left.  We can make CCW triangles from up->Dst. */
+      while( lo->Lnext != up && (EdgeGoesRight( up->Lprev )
+	     || EdgeSign( up->Dst, up->Org, up->Lprev->Org ) >= 0 )) {
+	GLUhalfEdge *tempHalfEdge= __gl_meshConnect( up, up->Lprev );
+	if (tempHalfEdge == NULL) return 0;
+	up = tempHalfEdge->Sym;
+      }
+      up = up->Lnext;
+    }
+  }
+
+  /* Now lo->Org == up->Dst == the leftmost vertex.  The remaining region
+   * can be tessellated in a fan from this leftmost vertex.
+   */
+  assert( lo->Lnext != up );
+  while( lo->Lnext->Lnext != up ) {
+    GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
+    if (tempHalfEdge == NULL) return 0;
+    lo = tempHalfEdge->Sym;
+  }
+
+  return 1;
+}
+
+
+/* __gl_meshTessellateInterior( mesh ) tessellates each region of
+ * the mesh which is marked "inside" the polygon.  Each such region
+ * must be monotone.
+ */
+int __gl_meshTessellateInterior( GLUmesh *mesh )
+{
+  GLUface *f, *next;
+
+  /*LINTED*/
+  for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
+    /* Make sure we don''t try to tessellate the new triangles. */
+    next = f->next;
+    if( f->inside ) {
+      if ( !__gl_meshTessellateMonoRegion( f ) ) return 0;
+    }
+  }
+
+  return 1;
+}
+
+
+/* __gl_meshDiscardExterior( mesh ) zaps (ie. sets to NULL) all faces
+ * which are not marked "inside" the polygon.  Since further mesh operations
+ * on NULL faces are not allowed, the main purpose is to clean up the
+ * mesh so that exterior loops are not represented in the data structure.
+ */
+void __gl_meshDiscardExterior( GLUmesh *mesh )
+{
+  GLUface *f, *next;
+
+  /*LINTED*/
+  for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
+    /* Since f will be destroyed, save its next pointer. */
+    next = f->next;
+    if( ! f->inside ) {
+      __gl_meshZapFace( f );
+    }
+  }
+}
+
+#define MARKED_FOR_DELETION	0x7fffffff
+
+/* __gl_meshSetWindingNumber( mesh, value, keepOnlyBoundary ) resets the
+ * winding numbers on all edges so that regions marked "inside" the
+ * polygon have a winding number of "value", and regions outside
+ * have a winding number of 0.
+ *
+ * If keepOnlyBoundary is TRUE, it also deletes all edges which do not
+ * separate an interior region from an exterior one.
+ */
+int __gl_meshSetWindingNumber( GLUmesh *mesh, int value,
+			        GLboolean keepOnlyBoundary )
+{
+  GLUhalfEdge *e, *eNext;
+
+  for( e = mesh->eHead.next; e != &mesh->eHead; e = eNext ) {
+    eNext = e->next;
+    if( e->Rface->inside != e->Lface->inside ) {
+
+      /* This is a boundary edge (one side is interior, one is exterior). */
+      e->winding = (e->Lface->inside) ? value : -value;
+    } else {
+
+      /* Both regions are interior, or both are exterior. */
+      if( ! keepOnlyBoundary ) {
+	e->winding = 0;
+      } else {
+	if ( !__gl_meshDelete( e ) ) return 0;
+      }
+    }
+  }
+  return 1;
+}