364 lines
10 KiB
C++
Executable File
364 lines
10 KiB
C++
Executable File
//-----------------------------------------------------------------------------
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// Decimator
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// based on "A Simple, Fast, and Effective Polygon Reduction Algorithm"
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// by Stan Melax from Game Developer Magazine, November 1998
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//-----------------------------------------------------------------------------
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#pragma warning ( disable: 4786 4018 )
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#include "DTSUtil.h"
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#include "DTSDecimator.h"
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namespace DTS
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{
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static std::vector<DecimatorVertex *> vertices;
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static std::vector<DecimatorTriangle *> triangles;
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DecimatorTriangle::DecimatorTriangle(DecimatorVertex *v0,DecimatorVertex *v1,DecimatorVertex *v2, S32 _type){
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assert(v0!=v1 && v1!=v2 && v2!=v0);
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vertex[0]=v0;
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vertex[1]=v1;
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vertex[2]=v2;
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ComputeNormal();
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triangles.push_back(this);
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for(S32 i=0;i<3;i++) {
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vertex[i]->face.push_back(this);
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for(S32 j=0;j<3;j++) if(i!=j) {
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addUniqueElement(vertex[i]->neighbor, vertex[j]);
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}
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}
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type = _type;
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}
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DecimatorTriangle::~DecimatorTriangle(){
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S32 i;
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delElement( triangles, this );
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for(i=0;i<3;i++) {
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if(vertex[i]) delElement(vertex[i]->face,this);
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}
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for(i=0;i<3;i++) {
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S32 i2 = (i+1)%3;
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if(!vertex[i] || !vertex[i2]) continue;
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vertex[i ]->RemoveIfNonNeighbor(vertex[i2]);
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vertex[i2]->RemoveIfNonNeighbor(vertex[i ]);
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}
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}
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S32 DecimatorTriangle::HasVertex(DecimatorVertex *v) {
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return (v==vertex[0] ||v==vertex[1] || v==vertex[2]);
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}
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void DecimatorTriangle::ComputeNormal(){
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Point v0=vertex[0]->position;
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Point v1=vertex[1]->position;
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Point v2=vertex[2]->position;
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Point e1 = v1 - v0;
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Point e2 = v2 - v1;
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crossProduct( e1, e2, &normal );
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normal.normalize();
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}
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void DecimatorTriangle::ReplaceVertex(DecimatorVertex *vold,DecimatorVertex *vnew) {
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assert(vold && vnew);
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assert(vold==vertex[0] || vold==vertex[1] || vold==vertex[2]);
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assert(vnew!=vertex[0] && vnew!=vertex[1] && vnew!=vertex[2]);
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if(vold==vertex[0]){
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vertex[0]=vnew;
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}
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else if(vold==vertex[1]){
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vertex[1]=vnew;
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}
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else {
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assert(vold==vertex[2]);
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vertex[2]=vnew;
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}
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S32 i;
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delElement(vold->face,this);
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assert(!containsElement(vnew->face,this));
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vnew->face.push_back(this);
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for(i=0;i<3;i++) {
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vold->RemoveIfNonNeighbor(vertex[i]);
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vertex[i]->RemoveIfNonNeighbor(vold);
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}
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for(i=0;i<3;i++) {
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assert(containsElement(vertex[i]->face,this)==1);
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for(S32 j=0;j<3;j++) if(i!=j) {
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addUniqueElement( vertex[i]->neighbor, vertex[j]);
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}
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}
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ComputeNormal();
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}
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DecimatorVertex::DecimatorVertex(Point v,S32 _id) {
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position =v;
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id=_id;
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vertices.push_back(this);
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}
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DecimatorVertex::~DecimatorVertex(){
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assert(face.size()==0);
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while(neighbor.size()) {
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delElement(neighbor[0]->neighbor,this);
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delElement(neighbor,neighbor[0]);
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}
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delElement(vertices,this);
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}
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void DecimatorVertex::RemoveIfNonNeighbor(DecimatorVertex *n) {
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// removes n from neighbor list if n isn't a neighbor.
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if(!containsElement(neighbor,n)) return;
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for(S32 i=0;i<face.size();i++) {
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if(face[i]->HasVertex(n)) return;
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}
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delElement(neighbor,n);
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}
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S32 DecimatorVertex::IsBorder()
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{
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S32 i,j;
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for(i=0;i<neighbor.size();i++)
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{
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S32 count=0;
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for(j=0;j<face.size();j++)
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{
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if(face[j]->HasVertex(neighbor[i]))
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{
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count++;
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}
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}
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assert(count>0);
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if(count==1)
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{
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return 1;
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}
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}
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return 0;
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}
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F32 Decimator::ComputeEdgeCollapseCost(DecimatorVertex *src,DecimatorVertex *dest) {
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// if we collapse edge src/dest by moving src to dest then how
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// much different will the model change, i.e. how much "error".
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// Texture, vertex normal, and border vertex code was removed
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// to keep this demo as simple as possible.
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// The method of determining cost was designed in order
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// to exploit small and coplanar regions for
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// effective polygon reduction.
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// Is is possible to add some checks here to see if "folds"
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// would be generated. i.e. normal of a remaining face gets
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// flipped. I never seemed to run into this problem and
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// therefore never added code to detect this case.
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S32 i;
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Point p = dest->position - src->position;
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F32 edgelength = p.length();
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F32 curvature = 0;
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// find the "sides" triangles that are on the edge uv
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std::vector<DecimatorTriangle *> sides;
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for( i = 0; i < src->face.size(); i++ )
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{
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if( src->face[i]->HasVertex( dest ) )
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{
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sides.push_back( src->face[i] );
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}
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}
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if(src->IsBorder() )
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{
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if( sides.size() > 1 )
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{
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curvature = 1;
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}
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else
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{
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curvature = 1;
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}
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}
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else
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{
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// use the triangle facing most away from the sides
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// to determine our curvature term
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for( i = 0; i < src->face.size(); i++ )
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{
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F32 mincurv = 1; // curve for face i and closer side to it
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for( S32 j = 0; j < sides.size(); j++ )
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{
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// use dot product of face normals. '^' defined in Point
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F32 dotprod = dotProduct( src->face[i]->normal, sides[j]->normal );
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mincurv = getmin( mincurv, ( 1.0f - dotprod ) * 0.5f );
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}
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curvature = getmax( curvature, mincurv );
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}
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}
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/*
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// check for texture seam ripping
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S32 nomatch=0;
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for(i=0;i<src->face.num;i++) {
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for(S32 j=0;j<sides.num;j++) {
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// perhaps we should actually compare the positions in uv space
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if(src->face[i]->texat(src) == sides[j]->texat(src)) break;
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}
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if(j==sides.num)
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{
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// we didn't find a triangle with edge uv that shares texture coordinates
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// with face i at vertex src
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nomatch++;
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}
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}
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if(nomatch) {
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curvature=1;
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}
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*/
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return edgelength * curvature;
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}
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void Decimator::ComputeEdgeCostAtVertex(DecimatorVertex *v) {
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// compute the edge collapse cost for all edges that start
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// from vertex v. Since we are only interested in reducing
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// the object by selecting the min cost edge at each step, we
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// only cache the cost of the least cost edge at this vertex
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// (in member variable collapse) as well as the value of the
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// cost (in member variable objdist).
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if(v->neighbor.size()==0) {
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// v doesn't have neighbors so it costs nothing to collapse
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v->collapse=NULL;
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v->objdist=-0.01f;
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return;
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}
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v->objdist = 1000000;
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v->collapse=NULL;
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// search all neighboring edges for "least cost" edge
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for(S32 i=0;i<v->neighbor.size();i++) {
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F32 dist;
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dist = ComputeEdgeCollapseCost(v,v->neighbor[i]);
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if(dist<v->objdist) {
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v->collapse=v->neighbor[i]; // candidate for edge collapse
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v->objdist=dist; // cost of the collapse
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}
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}
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}
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void Decimator::ComputeAllEdgeCollapseCosts() {
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// For all the edges, compute the difference it would make
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// to the model if it was collapsed. The least of these
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// per vertex is cached in each vertex object.
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for(S32 i=0;i<vertices.size();i++) {
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ComputeEdgeCostAtVertex(vertices[i]);
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}
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}
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void Decimator::Collapse(DecimatorVertex *u,DecimatorVertex *v){
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// Collapse the edge uv by moving vertex u onto v
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// Actually remove tris on uv, then update tris that
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// have u to have v, and then remove u.
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if(!v) {
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// u is a vertex all by itself so just delete it
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delete u;
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return;
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}
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S32 i;
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std::vector<DecimatorVertex *>tmp;
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// make tmp a list of all the neighbors of u
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for(i=0;i<u->neighbor.size();i++) {
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tmp.push_back(u->neighbor[i]);
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}
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// delete triangles on edge uv:
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for(i=u->face.size()-1;i>=0;i--) {
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if(u->face[i]->HasVertex(v)) {
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delete(u->face[i]);
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}
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}
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// update remaining triangles to have v instead of u
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for(i=u->face.size()-1;i>=0;i--) {
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u->face[i]->ReplaceVertex(u,v);
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}
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delete u;
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// recompute the edge collapse costs for neighboring vertices
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for(i=0;i<tmp.size();i++) {
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ComputeEdgeCostAtVertex(tmp[i]);
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}
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}
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DecimatorVertex *Decimator::MinimumCostEdge(){
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// Find the edge that when collapsed will affect model the least.
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// This function actually returns a Vertex, the second vertex
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// of the edge (collapse candidate) is stored in the vertex data.
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// Serious optimization opportunity here: this function currently
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// does a sequential search through an unsorted list :-(
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// Our algorithm could be O(n*lg(n)) instead of O(n*n)
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DecimatorVertex *mn=vertices[0];
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for(S32 i=0;i<vertices.size();i++) {
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if(vertices[i]->objdist < mn->objdist) {
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mn = vertices[i];
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}
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}
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return mn;
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}
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// Public interface
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Decimator::Decimator(std::vector<Primitive>& faces, std::vector<U16>& indices, std::vector<Point>& verts)
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{
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// Add the vertices
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for( S32 i = 0; i < verts.size(); i++ )
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{
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DecimatorVertex *v = new DecimatorVertex( verts[i], i );
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}
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// Add the faces
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for( S32 i = 0; i < faces.size(); i++ )
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{
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DecimatorTriangle *t=new DecimatorTriangle(
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vertices[indices[faces[i].firstElement]],
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vertices[indices[faces[i].firstElement+1]],
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vertices[indices[faces[i].firstElement+2]],
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faces[i].type );
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}
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ComputeAllEdgeCollapseCosts(); // cache all edge collapse costs
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}
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Decimator::~Decimator()
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{
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for( S32 i = triangles.size() - 1; i >= 0; i-- )
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{
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DecimatorTriangle *tmp = triangles[i];
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//triangles.Remove(tmp);
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delete tmp;
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}
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for( S32 i = vertices.size() - 1; i >= 0; i-- )
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{
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DecimatorVertex *tmp = vertices[i];
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//vertices.Remove(tmp);
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delete tmp;
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}
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}
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void Decimator::ReduceMesh( S32 faceCount )
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{
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// reduce the object
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while(triangles.size() > faceCount)
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{
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// get the next vertex to collapse
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DecimatorVertex *mn = MinimumCostEdge();
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// Collapse this edge
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Collapse(mn,mn->collapse);
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}
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primitives.empty();
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indices.empty();
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// Build our new primitive and index list
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for( S32 i = 0; i < triangles.size(); i++ )
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{
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if( triangles[i]->vertex[0] != NULL && triangles[i]->vertex[1] != NULL && triangles[i]->vertex[2] != NULL )
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{
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Primitive p;
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p.firstElement = indices.size();
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p.numElements = 3;
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p.type = triangles[i]->type;
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primitives.push_back( p );
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indices.push_back( triangles[i]->vertex[0]->id );
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indices.push_back( triangles[i]->vertex[1]->id );
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indices.push_back( triangles[i]->vertex[2]->id );
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}
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}
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}
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}
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