/*
* SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
* Copyright (C) 1991-2000 Silicon Graphics, Inc. All Rights Reserved.
*
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* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice including the dates of first publication and
* either this permission notice or a reference to
* http://oss.sgi.com/projects/FreeB/
* shall be included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* SILICON GRAPHICS, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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*
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* Silicon Graphics, Inc.
*/
/*
** Author: Eric Veach, July 1994.
**
*/
#include "gluos.h"
#include
#include "geom.h"
#include "mesh.h"
#include "tessmono.h"
#include
#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;
}