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202 lines
7.1 KiB
C
202 lines
7.1 KiB
C
/*
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* SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
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* Copyright (C) 1991-2000 Silicon Graphics, Inc. All Rights Reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice including the dates of first publication and
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* either this permission notice or a reference to
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* http://oss.sgi.com/projects/FreeB/
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* shall be included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* SILICON GRAPHICS, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
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* OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Except as contained in this notice, the name of Silicon Graphics, Inc.
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* shall not be used in advertising or otherwise to promote the sale, use or
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* other dealings in this Software without prior written authorization from
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* Silicon Graphics, Inc.
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*/
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/*
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** Author: Eric Veach, July 1994.
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**
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*/
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#include "../prboom/SDL_opengl.h" // JDC
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//#include "gluos.h"
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#include <stdlib.h>
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#include "geom.h"
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#include "mesh.h"
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#include "tessmono.h"
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#include <assert.h>
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#define AddWinding(eDst,eSrc) (eDst->winding += eSrc->winding, \
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eDst->Sym->winding += eSrc->Sym->winding)
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/* __gl_meshTessellateMonoRegion( face ) tessellates a monotone region
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* (what else would it do??) The region must consist of a single
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* loop of half-edges (see mesh.h) oriented CCW. "Monotone" in this
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* case means that any vertical line intersects the interior of the
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* region in a single interval.
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*
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* Tessellation consists of adding interior edges (actually pairs of
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* half-edges), to split the region into non-overlapping triangles.
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*
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* The basic idea is explained in Preparata and Shamos (which I don''t
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* have handy right now), although their implementation is more
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* complicated than this one. The are two edge chains, an upper chain
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* and a lower chain. We process all vertices from both chains in order,
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* from right to left.
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*
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* The algorithm ensures that the following invariant holds after each
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* vertex is processed: the untessellated region consists of two
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* chains, where one chain (say the upper) is a single edge, and
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* the other chain is concave. The left vertex of the single edge
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* is always to the left of all vertices in the concave chain.
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*
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* Each step consists of adding the rightmost unprocessed vertex to one
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* of the two chains, and forming a fan of triangles from the rightmost
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* of two chain endpoints. Determining whether we can add each triangle
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* to the fan is a simple orientation test. By making the fan as large
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* as possible, we restore the invariant (check it yourself).
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*/
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int __gl_meshTessellateMonoRegion( GLUface *face )
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{
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GLUhalfEdge *up, *lo;
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/* All edges are oriented CCW around the boundary of the region.
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* First, find the half-edge whose origin vertex is rightmost.
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* Since the sweep goes from left to right, face->anEdge should
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* be close to the edge we want.
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*/
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up = face->anEdge;
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assert( up->Lnext != up && up->Lnext->Lnext != up );
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for( ; VertLeq( up->Dst, up->Org ); up = up->Lprev )
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;
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for( ; VertLeq( up->Org, up->Dst ); up = up->Lnext )
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;
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lo = up->Lprev;
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while( up->Lnext != lo ) {
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if( VertLeq( up->Dst, lo->Org )) {
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/* up->Dst is on the left. It is safe to form triangles from lo->Org.
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* The EdgeGoesLeft test guarantees progress even when some triangles
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* are CW, given that the upper and lower chains are truly monotone.
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*/
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while( lo->Lnext != up && (EdgeGoesLeft( lo->Lnext )
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|| EdgeSign( lo->Org, lo->Dst, lo->Lnext->Dst ) <= 0 )) {
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GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
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if (tempHalfEdge == NULL) return 0;
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lo = tempHalfEdge->Sym;
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}
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lo = lo->Lprev;
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} else {
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/* lo->Org is on the left. We can make CCW triangles from up->Dst. */
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while( lo->Lnext != up && (EdgeGoesRight( up->Lprev )
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|| EdgeSign( up->Dst, up->Org, up->Lprev->Org ) >= 0 )) {
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GLUhalfEdge *tempHalfEdge= __gl_meshConnect( up, up->Lprev );
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if (tempHalfEdge == NULL) return 0;
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up = tempHalfEdge->Sym;
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}
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up = up->Lnext;
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}
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}
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/* Now lo->Org == up->Dst == the leftmost vertex. The remaining region
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* can be tessellated in a fan from this leftmost vertex.
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*/
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assert( lo->Lnext != up );
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while( lo->Lnext->Lnext != up ) {
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GLUhalfEdge *tempHalfEdge= __gl_meshConnect( lo->Lnext, lo );
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if (tempHalfEdge == NULL) return 0;
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lo = tempHalfEdge->Sym;
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}
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return 1;
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}
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/* __gl_meshTessellateInterior( mesh ) tessellates each region of
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* the mesh which is marked "inside" the polygon. Each such region
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* must be monotone.
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*/
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int __gl_meshTessellateInterior( GLUmesh *mesh )
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{
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GLUface *f, *next;
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/*LINTED*/
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for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
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/* Make sure we don''t try to tessellate the new triangles. */
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next = f->next;
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if( f->inside ) {
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if ( !__gl_meshTessellateMonoRegion( f ) ) return 0;
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}
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}
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return 1;
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}
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/* __gl_meshDiscardExterior( mesh ) zaps (ie. sets to NULL) all faces
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* which are not marked "inside" the polygon. Since further mesh operations
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* on NULL faces are not allowed, the main purpose is to clean up the
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* mesh so that exterior loops are not represented in the data structure.
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*/
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void __gl_meshDiscardExterior( GLUmesh *mesh )
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{
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GLUface *f, *next;
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/*LINTED*/
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for( f = mesh->fHead.next; f != &mesh->fHead; f = next ) {
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/* Since f will be destroyed, save its next pointer. */
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next = f->next;
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if( ! f->inside ) {
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__gl_meshZapFace( f );
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}
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}
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}
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#define MARKED_FOR_DELETION 0x7fffffff
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/* __gl_meshSetWindingNumber( mesh, value, keepOnlyBoundary ) resets the
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* winding numbers on all edges so that regions marked "inside" the
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* polygon have a winding number of "value", and regions outside
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* have a winding number of 0.
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*
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* If keepOnlyBoundary is TRUE, it also deletes all edges which do not
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* separate an interior region from an exterior one.
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*/
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int __gl_meshSetWindingNumber( GLUmesh *mesh, int value,
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GLboolean keepOnlyBoundary )
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{
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GLUhalfEdge *e, *eNext;
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for( e = mesh->eHead.next; e != &mesh->eHead; e = eNext ) {
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eNext = e->next;
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if( e->Rface->inside != e->Lface->inside ) {
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/* This is a boundary edge (one side is interior, one is exterior). */
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e->winding = (e->Lface->inside) ? value : -value;
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} else {
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/* Both regions are interior, or both are exterior. */
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if( ! keepOnlyBoundary ) {
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e->winding = 0;
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} else {
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if ( !__gl_meshDelete( e ) ) return 0;
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}
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}
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}
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return 1;
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}
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