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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.
**
** $Date: 2001/03/17 00:25:41 $ $Revision: 1.1 $
*/
/*
*monoPolyPart.C
*
*To partition a v-monotone polygon into some uv-monotone polygons.
*The algorithm is different from the general monotone partition algorithm.
*while the general monotone partition algorithm works for this special case,
*but it is more expensive (O(nlogn)). The algorithm implemented here takes
*advantage of the fact that the input is a v-monotone polygon and it is
*conceptually simpler and computationally cheaper (a linear time algorithm).
*The algorithm is described in Zicheng Liu's paper
* "Quality-Oriented Linear Time Tessellation".
*/
#include <stdlib.h>
#include <stdio.h>
#include "directedLine.h"
#include "monoPolyPart.h"
/*a vertex is u_maximal if both of its two neightbors are to the left of this
*vertex
*/
static Int is_u_maximal(directedLine* v)
{
if (compV2InX(v->getPrev()->head(), v->head()) == -1 &&
compV2InX(v->getNext()->head(), v->head()) == -1)
return 1;
else
return 0;
}
/*a vertex is u_minimal if both of its two neightbors are to the right of this
*vertex
*/
static Int is_u_minimal(directedLine* v)
{
if (compV2InX(v->getPrev()->head(), v->head()) == 1 &&
compV2InX(v->getNext()->head(), v->head()) == 1)
return 1;
else
return 0;
}
/*poly: a v-monotone polygon
*return: a linked list of uv-monotone polygons.
*/
directedLine* monoPolyPart(directedLine* polygon)
{
//handle special cases:
if(polygon == NULL)
return NULL;
if(polygon->getPrev() == polygon)
return polygon;
if(polygon->getPrev() == polygon->getNext())
return polygon;
if(polygon->getPrev()->getPrev() == polygon->getNext())
return polygon;
//find the top and bottom vertexes
directedLine *tempV, *topV, *botV;
topV = botV = polygon;
for(tempV = polygon->getNext(); tempV != polygon; tempV = tempV->getNext())
{
if(compV2InY(topV->head(), tempV->head())<0) {
topV = tempV;
}
if(compV2InY(botV->head(), tempV->head())>0) {
botV = tempV;
}
}
//initilization
directedLine *A, *B, *C, *D, *G, *H;
//find A:the first u_maximal vertex on the left chain
//and C: the left most vertex between top and A
A = NULL;
C = topV;
for(tempV=topV->getNext(); tempV != botV; tempV = tempV->getNext())
{
if(tempV->head()[0] < C->head()[0])
C = tempV;
if(is_u_maximal(tempV))
{
A = tempV;
break;
}
}
if(A == NULL)
{
A = botV;
if(A->head()[0] < C->head()[0])
C = A;
}
//find B: the first u_minimal vertex on the right chain
//and D: the right most vertex between top and B
B = NULL;
D = topV;
for(tempV=topV->getPrev(); tempV != botV; tempV = tempV->getPrev())
{
if(tempV->head()[0] > D->head()[0])
D = tempV;
if(is_u_minimal(tempV))
{
B = tempV;
break;
}
}
if(B == NULL)
{
B = botV;
if(B->head()[0] > D->head()[0])
D = B;
}
//error checking XXX
if(C->head()[0] >= D->head()[0])
return polygon;
//find G on the left chain that is right above B
for(tempV=topV; compV2InY(tempV->head(), B->head()) == 1; tempV=tempV->getNext());
G = tempV->getPrev();
//find H on the right chain that is right above A
for(tempV=topV; compV2InY(tempV->head(), A->head()) == 1; tempV = tempV->getPrev());
H = tempV->getNext();
//Main Loop
directedLine* ret = NULL;
directedLine* currentPolygon = polygon;
while(1)
{
//if both B and D are equal to botV, then this polygon is already
//u-monotone
if(A == botV && B == botV)
{
ret = currentPolygon->insertPolygon(ret);
return ret;
}
else //not u-monotone
{
directedLine *ret_p1, *ret_p2;
if(compV2InY(A->head(),B->head()) == 1) //A is above B
{
directedLine* E = NULL;
for(tempV = C; tempV != D; tempV = tempV->getPrev())
{
if(tempV->head()[0] >= A->head()[0])
{
E = tempV;
break;
}
}
if(E == NULL)
E = D;
if(E->head()[0]> H->head()[0])
E = H;
//connect AE and output polygon ECA
polygon->connectDiagonal_2slines(A, E,
&ret_p1,
&ret_p2,
NULL);
ret = ret_p2->insertPolygon(ret);
currentPolygon = ret_p1;
if(E == D)
D = ret_p1;
if(E == H)
H = ret_p1;
if(G->head()[1] >= A->head()[1])
G = A;
//update A to be the next u-maxiaml vertex on left chain
//and C the leftmost vertex between the old A and the new A
C = A;
for(tempV = A->getNext(); tempV != botV; tempV = tempV->getNext())
{
if(tempV->head()[0] < C->head()[0])
C = tempV;
if(is_u_maximal(tempV))
{
A = tempV;
break;
}
}
if(tempV == botV)
{
A = botV;
if(botV->head()[0] < C->head()[0])
C = botV;
}
//update H
if(A == botV)
H = botV;
else
{
for(tempV = H; compV2InY(tempV->head(), A->head()) == 1; tempV = tempV->getPrev());
H = tempV->getNext();
}
}
else //A is below B
{
directedLine* F = NULL;
for(tempV = D; tempV != C; tempV = tempV->getNext())
{
if(tempV->head()[0] <= B->head()[0])
{
F = tempV;
break;
}
}
if(F == NULL)
F = C;
if(F->head()[0] < G->head()[0])
F = G;
//connect FB
polygon->connectDiagonal_2slines(F, B,
&ret_p1,
&ret_p2,
NULL);
ret = ret_p2->insertPolygon(ret);
currentPolygon = ret_p1;
B = ret_p1;
if(H ->head()[1] >= B->head()[1])
H = ret_p1;
//update B to be the next u-minimal vertex on right chain
//and D the rightmost vertex between the old B and the new B
D = B;
for(tempV = B->getPrev(); tempV != botV; tempV = tempV->getPrev())
{
if(tempV->head()[0] > D->head()[0])
D = tempV;
if(is_u_minimal(tempV))
{
B = tempV;
break;
}
}
if(tempV == botV)
{
B = botV;
if(botV->head()[0] > D->head()[0])
D = botV;
}
//update G
if(B == botV)
G = botV;
else
{
for(tempV = G; compV2InY(tempV->head(), B->head()) == 1; tempV = tempV->getNext());
G = tempV->getPrev();
}
} //end of A is below B
} //end not u-monotone
} //end of main loop
}
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