2 * SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
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31 ** Author: Eric Veach, July 1994.
49 /* This structure remembers the information we need about a primitive
50 * to be able to render it later, once we have determined which
51 * primitive is able to use the most triangles.
54 long size; /* number of triangles used */
55 GLUhalfEdge *eStart; /* edge where this primitive starts */
56 void (*render)(GLUtesselator *, GLUhalfEdge *, long);
57 /* routine to render this primitive */
60 static struct FaceCount MaximumFan( GLUhalfEdge *eOrig );
61 static struct FaceCount MaximumStrip( GLUhalfEdge *eOrig );
63 static void RenderFan( GLUtesselator *tess, GLUhalfEdge *eStart, long size );
64 static void RenderStrip( GLUtesselator *tess, GLUhalfEdge *eStart, long size );
65 static void RenderTriangle( GLUtesselator *tess, GLUhalfEdge *eStart,
68 static void RenderMaximumFaceGroup( GLUtesselator *tess, GLUface *fOrig );
69 static void RenderLonelyTriangles( GLUtesselator *tess, GLUface *head );
73 /************************ Strips and Fans decomposition ******************/
75 /* __gl_renderMesh( tess, mesh ) takes a mesh and breaks it into triangle
76 * fans, strips, and separate triangles. A substantial effort is made
77 * to use as few rendering primitives as possible (ie. to make the fans
78 * and strips as large as possible).
80 * The rendering output is provided as callbacks (see the api).
82 void __gl_renderMesh( GLUtesselator *tess, GLUmesh *mesh )
86 /* Make a list of separate triangles so we can render them all at once */
87 tess->lonelyTriList = NULL;
89 for( f = mesh->fHead.next; f != &mesh->fHead; f = f->next ) {
92 for( f = mesh->fHead.next; f != &mesh->fHead; f = f->next ) {
94 /* We examine all faces in an arbitrary order. Whenever we find
95 * an unprocessed face F, we output a group of faces including F
96 * whose size is maximum.
98 if( f->inside && ! f->marked ) {
99 RenderMaximumFaceGroup( tess, f );
103 if( tess->lonelyTriList != NULL ) {
104 RenderLonelyTriangles( tess, tess->lonelyTriList );
105 tess->lonelyTriList = NULL;
110 static void RenderMaximumFaceGroup( GLUtesselator *tess, GLUface *fOrig )
112 /* We want to find the largest triangle fan or strip of unmarked faces
113 * which includes the given face fOrig. There are 3 possible fans
114 * passing through fOrig (one centered at each vertex), and 3 possible
115 * strips (one for each CCW permutation of the vertices). Our strategy
116 * is to try all of these, and take the primitive which uses the most
117 * triangles (a greedy approach).
119 GLUhalfEdge *e = fOrig->anEdge;
120 struct FaceCount max, newFace;
124 max.render = &RenderTriangle;
126 if( ! tess->flagBoundary ) {
127 newFace = MaximumFan( e ); if( newFace.size > max.size ) { max = newFace; }
128 newFace = MaximumFan( e->Lnext ); if( newFace.size > max.size ) { max = newFace; }
129 newFace = MaximumFan( e->Lprev ); if( newFace.size > max.size ) { max = newFace; }
131 newFace = MaximumStrip( e ); if( newFace.size > max.size ) { max = newFace; }
132 newFace = MaximumStrip( e->Lnext ); if( newFace.size > max.size ) { max = newFace; }
133 newFace = MaximumStrip( e->Lprev ); if( newFace.size > max.size ) { max = newFace; }
135 (*(max.render))( tess, max.eStart, max.size );
139 /* Macros which keep track of faces we have marked temporarily, and allow
140 * us to backtrack when necessary. With triangle fans, this is not
141 * really necessary, since the only awkward case is a loop of triangles
142 * around a single origin vertex. However with strips the situation is
143 * more complicated, and we need a general tracking method like the
146 #define Marked(f) (! (f)->inside || (f)->marked)
148 #define AddToTrail(f,t) ((f)->trail = (t), (t) = (f), (f)->marked = TRUE)
150 #define FreeTrail(t) do { \
151 while( (t) != NULL ) { \
152 (t)->marked = FALSE; t = (t)->trail; \
154 } while(0) /* absorb trailing semicolon */
158 static struct FaceCount MaximumFan( GLUhalfEdge *eOrig )
160 /* eOrig->Lface is the face we want to render. We want to find the size
161 * of a maximal fan around eOrig->Org. To do this we just walk around
162 * the origin vertex as far as possible in both directions.
164 struct FaceCount newFace = { 0, NULL, &RenderFan };
165 GLUface *trail = NULL;
168 for( e = eOrig; ! Marked( e->Lface ); e = e->Onext ) {
169 AddToTrail( e->Lface, trail );
172 for( e = eOrig; ! Marked( e->Rface ); e = e->Oprev ) {
173 AddToTrail( e->Rface, trail );
183 #define IsEven(n) (((n) & 1) == 0)
185 static struct FaceCount MaximumStrip( GLUhalfEdge *eOrig )
187 /* Here we are looking for a maximal strip that contains the vertices
188 * eOrig->Org, eOrig->Dst, eOrig->Lnext->Dst (in that order or the
189 * reverse, such that all triangles are oriented CCW).
191 * Again we walk forward and backward as far as possible. However for
192 * strips there is a twist: to get CCW orientations, there must be
193 * an *even* number of triangles in the strip on one side of eOrig.
194 * We walk the strip starting on a side with an even number of triangles;
195 * if both side have an odd number, we are forced to shorten one side.
197 struct FaceCount newFace = { 0, NULL, &RenderStrip };
198 long headSize = 0, tailSize = 0;
199 GLUface *trail = NULL;
200 GLUhalfEdge *e, *eTail, *eHead;
202 for( e = eOrig; ! Marked( e->Lface ); ++tailSize, e = e->Onext ) {
203 AddToTrail( e->Lface, trail );
206 if( Marked( e->Lface )) break;
207 AddToTrail( e->Lface, trail );
211 for( e = eOrig; ! Marked( e->Rface ); ++headSize, e = e->Dnext ) {
212 AddToTrail( e->Rface, trail );
215 if( Marked( e->Rface )) break;
216 AddToTrail( e->Rface, trail );
220 newFace.size = tailSize + headSize;
221 if( IsEven( tailSize )) {
222 newFace.eStart = eTail->Sym;
223 } else if( IsEven( headSize )) {
224 newFace.eStart = eHead;
226 /* Both sides have odd length, we must shorten one of them. In fact,
227 * we must start from eHead to guarantee inclusion of eOrig->Lface.
230 newFace.eStart = eHead->Onext;
238 static void RenderTriangle( GLUtesselator *tess, GLUhalfEdge *e, long size )
240 /* Just add the triangle to a triangle list, so we can render all
241 * the separate triangles at once.
244 AddToTrail( e->Lface, tess->lonelyTriList );
248 static void RenderLonelyTriangles( GLUtesselator *tess, GLUface *f )
250 /* Now we render all the separate triangles which could not be
251 * grouped into a triangle fan or strip.
255 int edgeState = -1; /* force edge state output for first vertex */
257 CALL_BEGIN_OR_BEGIN_DATA( GL_TRIANGLES );
259 for( ; f != NULL; f = f->trail ) {
260 /* Loop once for each edge (there will always be 3 edges) */
264 if( tess->flagBoundary ) {
265 /* Set the "edge state" to TRUE just before we output the
266 * first vertex of each edge on the polygon boundary.
268 newState = ! e->Rface->inside;
269 if( edgeState != newState ) {
270 edgeState = newState;
271 CALL_EDGE_FLAG_OR_EDGE_FLAG_DATA( edgeState );
274 CALL_VERTEX_OR_VERTEX_DATA( e->Org->data );
277 } while( e != f->anEdge );
279 CALL_END_OR_END_DATA();
283 static void RenderFan( GLUtesselator *tess, GLUhalfEdge *e, long size )
285 /* Render as many CCW triangles as possible in a fan starting from
286 * edge "e". The fan *should* contain exactly "size" triangles
287 * (otherwise we've goofed up somewhere).
289 CALL_BEGIN_OR_BEGIN_DATA( GL_TRIANGLE_FAN );
290 CALL_VERTEX_OR_VERTEX_DATA( e->Org->data );
291 CALL_VERTEX_OR_VERTEX_DATA( e->Dst->data );
293 while( ! Marked( e->Lface )) {
294 e->Lface->marked = TRUE;
297 CALL_VERTEX_OR_VERTEX_DATA( e->Dst->data );
301 CALL_END_OR_END_DATA();
305 static void RenderStrip( GLUtesselator *tess, GLUhalfEdge *e, long size )
307 /* Render as many CCW triangles as possible in a strip starting from
308 * edge "e". The strip *should* contain exactly "size" triangles
309 * (otherwise we've goofed up somewhere).
311 CALL_BEGIN_OR_BEGIN_DATA( GL_TRIANGLE_STRIP );
312 CALL_VERTEX_OR_VERTEX_DATA( e->Org->data );
313 CALL_VERTEX_OR_VERTEX_DATA( e->Dst->data );
315 while( ! Marked( e->Lface )) {
316 e->Lface->marked = TRUE;
319 CALL_VERTEX_OR_VERTEX_DATA( e->Org->data );
320 if( Marked( e->Lface )) break;
322 e->Lface->marked = TRUE;
325 CALL_VERTEX_OR_VERTEX_DATA( e->Dst->data );
329 CALL_END_OR_END_DATA();
333 /************************ Boundary contour decomposition ******************/
335 /* __gl_renderBoundary( tess, mesh ) takes a mesh, and outputs one
336 * contour for each face marked "inside". The rendering output is
337 * provided as callbacks (see the api).
339 void __gl_renderBoundary( GLUtesselator *tess, GLUmesh *mesh )
344 for( f = mesh->fHead.next; f != &mesh->fHead; f = f->next ) {
346 CALL_BEGIN_OR_BEGIN_DATA( GL_LINE_LOOP );
349 CALL_VERTEX_OR_VERTEX_DATA( e->Org->data );
351 } while( e != f->anEdge );
352 CALL_END_OR_END_DATA();
358 /************************ Quick-and-dirty decomposition ******************/
360 #define SIGN_INCONSISTENT 2
362 static int ComputeNormal( GLUtesselator *tess, GLdouble norm[3], int check )
364 * If check==FALSE, we compute the polygon normal and place it in norm[].
365 * If check==TRUE, we check that each triangle in the fan from v0 has a
366 * consistent orientation with respect to norm[]. If triangles are
367 * consistently oriented CCW, return 1; if CW, return -1; if all triangles
368 * are degenerate return 0; otherwise (no consistent orientation) return
372 CachedVertex *v0 = tess->cache;
373 CachedVertex *vn = v0 + tess->cacheCount;
375 GLdouble dot, xc, yc, zc, xp, yp, zp, n[3];
378 /* Find the polygon normal. It is important to get a reasonable
379 * normal even when the polygon is self-intersecting (eg. a bowtie).
380 * Otherwise, the computed normal could be very tiny, but perpendicular
381 * to the true plane of the polygon due to numerical noise. Then all
382 * the triangles would appear to be degenerate and we would incorrectly
383 * decompose the polygon as a fan (or simply not render it at all).
385 * We use a sum-of-triangles normal algorithm rather than the more
386 * efficient sum-of-trapezoids method (used in CheckOrientation()
387 * in normal.c). This lets us explicitly reverse the signed area
388 * of some triangles to get a reasonable normal in the self-intersecting
392 norm[0] = norm[1] = norm[2] = 0.0;
396 xc = vc->coords[0] - v0->coords[0];
397 yc = vc->coords[1] - v0->coords[1];
398 zc = vc->coords[2] - v0->coords[2];
400 xp = xc; yp = yc; zp = zc;
401 xc = vc->coords[0] - v0->coords[0];
402 yc = vc->coords[1] - v0->coords[1];
403 zc = vc->coords[2] - v0->coords[2];
405 /* Compute (vp - v0) cross (vc - v0) */
406 n[0] = yp*zc - zp*yc;
407 n[1] = zp*xc - xp*zc;
408 n[2] = xp*yc - yp*xc;
410 dot = n[0]*norm[0] + n[1]*norm[1] + n[2]*norm[2];
412 /* Reverse the contribution of back-facing triangles to get
413 * a reasonable normal for self-intersecting polygons (see above)
416 norm[0] += n[0]; norm[1] += n[1]; norm[2] += n[2];
418 norm[0] -= n[0]; norm[1] -= n[1]; norm[2] -= n[2];
420 } else if( dot != 0 ) {
421 /* Check the new orientation for consistency with previous triangles */
423 if( sign < 0 ) return SIGN_INCONSISTENT;
426 if( sign > 0 ) return SIGN_INCONSISTENT;
434 /* __gl_renderCache( tess ) takes a single contour and tries to render it
435 * as a triangle fan. This handles convex polygons, as well as some
436 * non-convex polygons if we get lucky.
438 * Returns TRUE if the polygon was successfully rendered. The rendering
439 * output is provided as callbacks (see the api).
441 GLboolean __gl_renderCache( GLUtesselator *tess )
443 CachedVertex *v0 = tess->cache;
444 CachedVertex *vn = v0 + tess->cacheCount;
449 if( tess->cacheCount < 3 ) {
450 /* Degenerate contour -- no output */
454 norm[0] = tess->normal[0];
455 norm[1] = tess->normal[1];
456 norm[2] = tess->normal[2];
457 if( norm[0] == 0 && norm[1] == 0 && norm[2] == 0 ) {
458 ComputeNormal( tess, norm, FALSE );
461 sign = ComputeNormal( tess, norm, TRUE );
462 if( sign == SIGN_INCONSISTENT ) {
463 /* Fan triangles did not have a consistent orientation */
467 /* All triangles were degenerate */
471 /* Make sure we do the right thing for each winding rule */
472 switch( tess->windingRule ) {
473 case GLU_TESS_WINDING_ODD:
474 case GLU_TESS_WINDING_NONZERO:
476 case GLU_TESS_WINDING_POSITIVE:
477 if( sign < 0 ) return TRUE;
479 case GLU_TESS_WINDING_NEGATIVE:
480 if( sign > 0 ) return TRUE;
482 case GLU_TESS_WINDING_ABS_GEQ_TWO:
486 CALL_BEGIN_OR_BEGIN_DATA( tess->boundaryOnly ? GL_LINE_LOOP
487 : (tess->cacheCount > 3) ? GL_TRIANGLE_FAN
490 CALL_VERTEX_OR_VERTEX_DATA( v0->data );
492 for( vc = v0+1; vc < vn; ++vc ) {
493 CALL_VERTEX_OR_VERTEX_DATA( vc->data );
496 for( vc = vn-1; vc > v0; --vc ) {
497 CALL_VERTEX_OR_VERTEX_DATA( vc->data );
500 CALL_END_OR_END_DATA();