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