virtualx-engine/drivers/convex_decomp/b2d_decompose.cpp

#include "b2d_decompose.h"
#include "b2Polygon.h"

namespace b2ConvexDecomp {


void add_to_res(Vector< Vector<Vector2> >& res,const b2Polygon& p_poly) {

	Vector<Vector2> arr;
	for(int i=0;i<p_poly.nVertices;i++) {

		arr.push_back(Vector2(p_poly.x[i],p_poly.y[i]));
	}

	res.push_back(arr);

}

static Vector< Vector<Vector2> > _b2d_decompose(const Vector<Vector2>& p_polygon) {


	Vector< Vector<Vector2> > res;
	if (p_polygon.size()<3)
		return res;

	b2Vec2 *polys = memnew_arr(b2Vec2,p_polygon.size());
	for(int i=0;i<p_polygon.size();i++)
		polys[i]=b2Vec2(p_polygon[i].x,p_polygon[i].y);


	b2Polygon *p = new b2Polygon(polys,p_polygon.size());
	b2Polygon* decomposed = new b2Polygon[p->nVertices - 2]; //maximum number of polys

	memdelete_arr(polys);

	int32 nPolys = DecomposeConvex(p, decomposed, p->nVertices - 2);
		//int32 extra = 0;
	for (int32 i = 0; i < nPolys; ++i) {
			//   b2FixtureDef* toAdd = &pdarray[i+extra];
			// *toAdd = *prototype;
			 //Hmm, shouldn't have to do all this...
			b2Polygon curr = decomposed[i];
			//TODO ewjordan: move this triangle handling to a better place so that
			//it happens even if this convenience function is not called.
			if (curr.nVertices == 3){
					//Check here for near-parallel edges, since we can't
					//handle this in merge routine
					for (int j=0; j<3; ++j){
						int32 lower = (j == 0) ? (curr.nVertices - 1) : (j - 1);
						int32 middle = j;
						int32 upper = (j == curr.nVertices - 1) ? (0) : (j + 1);
						float32 dx0 = curr.x[middle] - curr.x[lower]; float32 dy0 = curr.y[middle] - curr.y[lower];
						float32 dx1 = curr.x[upper] - curr.x[middle]; float32 dy1 = curr.y[upper] - curr.y[middle];
						float32 norm0 = sqrtf(dx0*dx0+dy0*dy0);	float32 norm1 = sqrtf(dx1*dx1+dy1*dy1);
						if ( !(norm0 > 0.0f && norm1 > 0.0f) ) {
							//Identical points, don't do anything!
							goto Skip;
						}
						dx0 /= norm0; dy0 /= norm0;
						dx1 /= norm1; dy1 /= norm1;
						float32 cross = dx0 * dy1 - dx1 * dy0;
						float32 dot = dx0*dx1 + dy0*dy1;
						if (fabs(cross) < b2_angularSlop && dot > 0) {
							//Angle too close, split the triangle across from this point.
							//This is guaranteed to result in two triangles that satify
							//the tolerance (one of the angles is 90 degrees)
							float32 dx2 = curr.x[lower] - curr.x[upper]; float32 dy2 = curr.y[lower] - curr.y[upper];
							float32 norm2 = sqrtf(dx2*dx2+dy2*dy2);
							if (norm2 == 0.0f) {
								goto Skip;
							}
							dx2 /= norm2; dy2 /= norm2;
							float32 thisArea = curr.GetArea();
							float32 thisHeight = 2.0f * thisArea / norm2;
							float32 buffer2 = dx2;
							dx2 = dy2; dy2 = -buffer2;
							//Make two new polygons
							//printf("dx2: %f, dy2: %f, thisHeight: %f, middle: %d\n",dx2,dy2,thisHeight,middle);
							float32 newX1[3] = { curr.x[middle]+dx2*thisHeight, curr.x[lower], curr.x[middle] };
							float32 newY1[3] = { curr.y[middle]+dy2*thisHeight, curr.y[lower], curr.y[middle] };
							float32 newX2[3] = { newX1[0], curr.x[middle], curr.x[upper] };
							float32 newY2[3] = { newY1[0], curr.y[middle], curr.y[upper] };
							b2Polygon p1(newX1,newY1,3);
							b2Polygon p2(newX2,newY2,3);
							if (p1.IsUsable()){
								add_to_res(res,p1);
								//++extra;
							} else if (B2_POLYGON_REPORT_ERRORS){
								printf("Didn't add unusable polygon.  Dumping vertices:\n");
								p1.print();
							}
							if (p2.IsUsable()){
								add_to_res(res,p2);

								//p2.AddTo(pdarray[i+extra]);

								//bd->CreateFixture(toAdd);
							} else if (B2_POLYGON_REPORT_ERRORS){
								printf("Didn't add unusable polygon.  Dumping vertices:\n");
								p2.print();
							}
							goto Skip;
						}
					}

			}
			if (decomposed[i].IsUsable()){
				add_to_res(res,decomposed[i]);

				//decomposed[i].AddTo(*toAdd);
				//bd->CreateFixture((const b2FixtureDef*)toAdd);
			} else if (B2_POLYGON_REPORT_ERRORS){
				printf("Didn't add unusable polygon.  Dumping vertices:\n");
				decomposed[i].print();
			}
Skip:
			;
	}
//	delete[] pdarray;
	delete[] decomposed;
	delete p;
	return res;// pdarray; //needs to be deleted after body is created

}

}


Vector< Vector<Vector2> > b2d_decompose(const Vector<Vector2>& p_polygon) {

	return b2ConvexDecomp::_b2d_decompose(p_polygon);


}