//----------------------------------------------------------------------------
static int WhichSide (const Line2& rkLine, int iEdgeQuantity,
const int* aiEdge, const Vector2* akPoint)
{
// establish which side of line hull is on
Real fC0;
for (int i1 = 0, i0 = iEdgeQuantity-1; i1 < iEdgeQuantity; i0 = i1++)
{
fC0 = rkLine.Normal().Dot(akPoint[aiEdge[i0]]);
if ( fC0 > rkLine.Constant()+gs_fEpsilon ) // hull on positive side
return +1;
if ( fC0 < rkLine.Constant()-gs_fEpsilon ) // hull on negative side
return -1;
fC0 = rkLine.Normal().Dot(akPoint[aiEdge[i1]]);
if ( fC0 > rkLine.Constant()+gs_fEpsilon ) // hull on positive side
return +1;
if ( fC0 < rkLine.Constant()-gs_fEpsilon ) // hull on negative side
return -1;
}
// hull is effectively collinear
return 0;
}
//----------------------------------------------------------------------------
static int OnSameSide (const Line2& rkLine, int iEdgeQuantity,
const int* aiEdge, const Vector2* akPoint)
{
// test if all points on same side of line Dot(N,X) = c
Real fC0;
int iPosSide = 0, iNegSide = 0;
for (int i1 = 0, i0 = iEdgeQuantity-1; i1 < iEdgeQuantity; i0 = i1++)
{
fC0 = rkLine.Normal().Dot(akPoint[aiEdge[i0]]);
if ( fC0 > rkLine.Constant() + gs_fEpsilon )
iPosSide++;
else if ( fC0 < rkLine.Constant() - gs_fEpsilon )
iNegSide++;
if ( iPosSide && iNegSide )
{
// line splits point set
return 0;
}
fC0 = rkLine.Normal().Dot(akPoint[aiEdge[i1]]);
if ( fC0 > rkLine.Constant() + gs_fEpsilon )
iPosSide++;
else if ( fC0 < rkLine.Constant() - gs_fEpsilon )
iNegSide++;
if ( iPosSide && iNegSide )
{
// line splits point set
return 0;
}
}
return iPosSide ? +1 : -1;
}
//----------------------------------------------------------------------------
bool Mgc::SeparatePointSets2D (int iQuantity0, const Vector2* akVertex0,
int iQuantity1, const Vector2* akVertex1, Line2& rkSeprLine)
{
// construct convex hull of point set 0
ConvexHull2D kHull0(iQuantity0,akVertex0);
kHull0.ByDivideAndConquer();
int iEdgeQuantity0 = kHull0.GetQuantity();
const int* aiEdge0 = kHull0.GetIndices();
// construct convex hull of point set 1
ConvexHull2D kHull1(iQuantity1,akVertex1);
kHull1.ByDivideAndConquer();
int iEdgeQuantity1 = kHull1.GetQuantity();
const int* aiEdge1 = kHull1.GetIndices();
// test edges of hull 0 for possible separation of points
int j0, j1, iI0, iI1, iSide0, iSide1;
Vector2 kDiff;
for (j1 = 0, j0 = iEdgeQuantity0-1; j1 < iEdgeQuantity0; j0 = j1++)
{
// lookup edge (assert: iI0 != iI1 )
iI0 = aiEdge0[j0];
iI1 = aiEdge0[j1];
// compute potential separating line (assert: (xNor,yNor) != (0,0))
kDiff = akVertex0[iI1] - akVertex0[iI0];
rkSeprLine.Normal() = kDiff.Cross();
rkSeprLine.Constant() = rkSeprLine.Normal().Dot(akVertex0[iI0]);
// determine if hull 1 is on same side of line
iSide1 = OnSameSide(rkSeprLine,iEdgeQuantity1,aiEdge1,akVertex1);
if ( iSide1 )
{
// determine which side of line hull 0 lies
iSide0 = WhichSide(rkSeprLine,iEdgeQuantity0,aiEdge0,akVertex0);
if ( iSide0*iSide1 <= 0 ) // line separates hulls
return true;
}
}
// test edges of hull 1 for possible separation of points
for (j1 = 0, j0 = iEdgeQuantity1-1; j1 < iEdgeQuantity1; j0 = j1++)
{
// lookup edge (assert: iI0 != iI1 )
iI0 = aiEdge1[j0];
iI1 = aiEdge1[j1];
// compute perpendicular to edge (assert: (xNor,yNor) != (0,0))
kDiff = akVertex1[iI1] - akVertex1[iI0];
rkSeprLine.Normal() = kDiff.Cross();
rkSeprLine.Constant() = rkSeprLine.Normal().Dot(akVertex1[iI0]);
// determine if hull 0 is on same side of line
iSide0 = OnSameSide(rkSeprLine,iEdgeQuantity0,aiEdge0,akVertex0);
if ( iSide0 )
{
// determine which side of line hull 1 lies
iSide1 = WhichSide(rkSeprLine,iEdgeQuantity1,aiEdge1,akVertex1);
if ( iSide0*iSide1 <= 0 ) // line separates hulls
return true;
}
}
return false;
}
