TGeoPolygon.cxx

Go to the documentation of this file.

// @(#)root/geom:$Id$
// Author: Mihaela Gheata   5/01/04

/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

/** \class TGeoPolygon
\ingroup Geometry_classes

An arbitrary polygon defined by vertices. The vertices
have to be defined CLOCKWISE in the XY plane, making either a convex
or concave polygon. No test for malformed polygons is performed.

A polygon is a 2D shape defined by vertices in the XY plane. It is used by
TGeoXtru class for computing Contains() and Safety(). Only the pointers to
the actual lists of XY values are used - these are not owned by the class.

To check if a point in XY plane is contained by a polygon, this is split
into an outscribed convex polygon and the remaining polygons of its subtraction
from the outscribed one. A point is INSIDE if it is
contained by the outscribed polygon but NOT by the remaining ones. Since these
can also be arbitrary polygons at their turn, a tree structure is formed:

~~~ {.cpp}
 P = Pconvex - (Pconvex-P)           where (-) means 'subtraction'
 Pconvex-P = P1 + P2 + ...           where (+) means 'union'
~~~

*Note that P1, P2, ... do not intersect each other and they are defined
by subsets of the list of vertices of P. They can be split in the same
way as P*

Therefore, if C(P) represents the Boolean : 'does P contains a given point?',
then:

~~~ {.cpp}
C(P) = C(Pconvex) .and. not(C(P1) | C(P2) | ...)
~~~

For creating a polygon without TGeoXtru class, one has to call the constructor
TGeoPolygon(nvert) and then SetXY(Double_t *x, Double_t *y) providing the
arrays of X and Y vertex positions (defined clockwise) that have to 'live' longer
than the polygon they will describe. This complication is due to efficiency reasons.
At the end one has to call the FinishPolygon() method.
*/

#include "TObjArray.h"
#include "TGeoPolygon.h"
#include "TMath.h"
#include "TGeoShape.h"
#include "TGeoManager.h"
#include "TVirtualGeoPainter.h"

ClassImp(TGeoPolygon)

////////////////////////////////////////////////////////////////////////////////
/// Dummy constructor.

TGeoPolygon::TGeoPolygon()
{
   fNvert   = 0;
   fNconvex = 0;
   fInd     = 0;
   fIndc    = 0;
   fX       = 0;
   fY       = 0;
   fDaughters = 0;
   SetConvex(kFALSE);
   TObject::SetBit(kGeoFinishPolygon, kFALSE);
}

////////////////////////////////////////////////////////////////////////////////
/// Default constructor.

TGeoPolygon::TGeoPolygon(Int_t nvert)
{
   if (nvert<3) {
      Fatal("Ctor", "Invalid number of vertices %i", nvert);
      return;
   }
   fNvert   = nvert;
   fNconvex = 0;
   fInd     = new Int_t[nvert];
   fIndc    = 0;
   fX       = 0;
   fY       = 0;
   fDaughters = 0;
   SetConvex(kFALSE);
   TObject::SetBit(kGeoFinishPolygon, kFALSE);
   SetNextIndex();
}

////////////////////////////////////////////////////////////////////////////////
/// Destructor

TGeoPolygon::~TGeoPolygon()
{
   if (fInd)  delete [] fInd;
   if (fIndc) delete [] fIndc;
   if (fDaughters) {
      fDaughters->Delete();
      delete fDaughters;
   }
}
////////////////////////////////////////////////////////////////////////////////
/// Computes area of the polygon in [length^2].

Double_t TGeoPolygon::Area() const
{
   Int_t ic,i,j;
   Double_t area = 0;
   // Compute area of the convex part
   for (ic=0; ic<fNvert; ic++) {
      i = fInd[ic];
      j = fInd[(ic+1)%fNvert];
      area += 0.5*(fX[i]*fY[j]-fX[j]*fY[i]);
   }
   return TMath::Abs(area);
}

////////////////////////////////////////////////////////////////////////////////
/// Check if a point given by X = point[0], Y = point[1] is inside the polygon.

Bool_t TGeoPolygon::Contains(const Double_t *point) const
{
   Int_t i;
   TGeoPolygon *poly;
   for (i=0; i<fNconvex; i++)
      if (!IsRightSided(point, fIndc[i], fIndc[(i+1)%fNconvex])) return kFALSE;
   if (!fDaughters) return kTRUE;
   Int_t nd = fDaughters->GetEntriesFast();
   for (i=0; i<nd; i++) {
      poly = (TGeoPolygon*)fDaughters->UncheckedAt(i);
      if (poly->Contains(point)) return kFALSE;
   }
   return kTRUE;
}

////////////////////////////////////////////////////////////////////////////////
/// Check polygon convexity.

void TGeoPolygon::ConvexCheck()
{
   if (fNvert==3) {
      SetConvex();
      return;
   }
   Int_t j,k;
   Double_t point[2];
   for (Int_t i=0; i<fNvert; i++) {
      j = (i+1)%fNvert;
      k = (i+2)%fNvert;
      point[0] = fX[fInd[k]];
      point[1] = fY[fInd[k]];
      if (!IsRightSided(point, fInd[i], fInd[j])) return;
   }
   SetConvex();
}

////////////////////////////////////////////////////////////////////////////////
/// Draw the polygon.

void TGeoPolygon::Draw(Option_t *)
{
   if (!gGeoManager) return;
   gGeoManager->GetGeomPainter()->DrawPolygon(this);
}

////////////////////////////////////////////////////////////////////////////////
/// Decompose polygon in a convex outscribed part and a list of daughter
/// polygons that have to be subtracted to get the actual one.

void TGeoPolygon::FinishPolygon()
{
   TObject::SetBit(kGeoFinishPolygon);
   // check convexity
   ConvexCheck();
   // find outscribed convex polygon indices
   OutscribedConvex();
   if (IsConvex()) {
//      printf(" -> polygon convex -> same indices\n");
      memcpy(fIndc, fInd, fNvert*sizeof(Int_t));
      return;
   }
//   printf(" -> polygon NOT convex\n");
   // make daughters if necessary
   if (IsConvex()) return;
   // ... algorithm here
   if (!fDaughters) fDaughters = new TObjArray();
   TGeoPolygon *poly = 0;
   Int_t indconv = 0;
   Int_t indnext, indback;
   Int_t nskip;
   while (indconv < fNconvex) {
      indnext = (indconv+1)%fNconvex;
      nskip = fIndc[indnext]-fIndc[indconv];
      if (nskip<0) nskip+=fNvert;
      if (nskip==1) {
         indconv++;
         continue;
      }
      // gap -> make polygon
      poly = new TGeoPolygon(nskip+1);
      poly->SetXY(fX,fY);
      poly->SetNextIndex(fInd[fIndc[indconv]]);
      poly->SetNextIndex(fInd[fIndc[indnext]]);
      indback = fIndc[indnext]-1;
      if (indback < 0) indback+=fNvert;
      while (indback != fIndc[indconv]) {
         poly->SetNextIndex(fInd[indback]);
         indback--;
         if (indback < 0) indback+=fNvert;
      }
      poly->FinishPolygon();
      fDaughters->Add(poly);
      indconv++;
   }
   for (indconv=0; indconv<fNconvex; indconv++) fIndc[indconv] = fInd[fIndc[indconv]];
}

////////////////////////////////////////////////////////////////////////////////
/// Fill list of vertices into provided arrays.

void TGeoPolygon::GetVertices(Double_t *x, Double_t *y) const
{
   memcpy(x, fX, fNvert*sizeof(Double_t));
   memcpy(y, fY, fNvert*sizeof(Double_t));
}

////////////////////////////////////////////////////////////////////////////////
/// Fill list of vertices of the convex outscribed polygon into provided arrays.

void TGeoPolygon::GetConvexVertices(Double_t *x, Double_t *y) const
{
   for (Int_t ic=0; ic<fNconvex; ic++) {
      x[ic] = fX[fIndc[ic]];
      y[ic] = fY[fIndc[ic]];
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Check if POINT is right-sided with respect to the segment defined by IND1 and IND2.

Bool_t TGeoPolygon::IsRightSided(const Double_t *point, Int_t ind1, Int_t ind2) const
{
   Double_t dot = (point[0]-fX[ind1])*(fY[ind2]-fY[ind1]) -
                  (point[1]-fY[ind1])*(fX[ind2]-fX[ind1]);
   if (!IsClockwise()) dot = -dot;
   if (dot<-1.E-10) return kFALSE;
   return kTRUE;
}

////////////////////////////////////////////////////////////////////////////////
/// Check if a segment [0..fNvert-1] belongs to the outscribed convex pgon.

Bool_t TGeoPolygon::IsSegConvex(Int_t i1, Int_t i2) const
{
   if (i2<0) i2=(i1+1)%fNvert;
   Double_t point[2];
   for (Int_t i=0; i<fNvert; i++) {
      if (i==i1 || i==i2) continue;
      point[0] = fX[fInd[i]];
      point[1] = fY[fInd[i]];
      if (!IsRightSided(point, fInd[i1], fInd[i2])) return kFALSE;
   }
   return kTRUE;
}

////////////////////////////////////////////////////////////////////////////////
/// Check for illegal crossings between non-consecutive segments

Bool_t TGeoPolygon::IsIllegalCheck() const
{
   if (fNvert<4) return kFALSE;
   Bool_t is_illegal = kFALSE;
   Double_t x1,y1,x2,y2,x3,y3,x4,y4;
   for (Int_t i=0; i<fNvert-2; i++) {
      // Check segment i
      for (Int_t j=i+2; j<fNvert; j++) {
         // Versus segment j
         if (i==0 && j==(fNvert-1)) continue;
         x1 = fX[i];
         y1 = fY[i];
         x2 = fX[i+1];
         y2 = fY[i+1];
         x3 = fX[j];
         y3 = fY[j];
         x4 = fX[(j+1)%fNvert];
         y4 = fY[(j+1)%fNvert];
         if (TGeoShape::IsSegCrossing(x1,y1,x2,y2,x3,y3,x4,y4)) {
            Error("IsIllegalCheck", "Illegal crossing of segment %d vs. segment %d", i,j);
            is_illegal = kTRUE;
         }
      }
   }
   return is_illegal;
}

////////////////////////////////////////////////////////////////////////////////
/// Compute indices for the outscribed convex polygon.

void TGeoPolygon::OutscribedConvex()
{
   fNconvex = 0;
   Int_t iseg = 0;
   Int_t ivnew;
   Bool_t conv;
   Int_t *indconv = new Int_t[fNvert];
   memset(indconv, 0, fNvert*sizeof(Int_t));
   while (iseg<fNvert) {
      if (!IsSegConvex(iseg)) {
         if (iseg+2 > fNvert) break;
         ivnew = (iseg+2)%fNvert;
         conv = kFALSE;
         // check iseg with next vertices
         while (ivnew) {
            if (IsSegConvex(iseg, ivnew)) {
               conv = kTRUE;
               break;
            }
            ivnew = (ivnew+1)%fNvert;
         }
         if (!conv) {
//            Error("OutscribedConvex","NO convex line connection to vertex %d\n", iseg);
            iseg++;
            continue;
         }
      } else {
         ivnew = (iseg+1)%fNvert;
      }
      // segment belonging to convex outscribed polygon
      if (!fNconvex) indconv[fNconvex++] = iseg;
      else if (indconv[fNconvex-1] != iseg) indconv[fNconvex++] = iseg;
      if (iseg<fNvert-1) indconv[fNconvex++] = ivnew;
      if (ivnew<iseg) break;
      iseg = ivnew;
   }
   if (!fNconvex) {
      delete [] indconv;
      Fatal("OutscribedConvex","cannot build outscribed convex");
      return;
   }
   fIndc = new Int_t[fNvert];
   memcpy(fIndc, indconv, fNconvex*sizeof(Int_t)); // does not contain real indices yet
   delete [] indconv;
}

////////////////////////////////////////////////////////////////////////////////
/// Compute minimum distance from POINT to any segment. Returns segment index.

Double_t TGeoPolygon::Safety(const Double_t *point, Int_t &isegment) const
{
   Int_t i1, i2;
   Double_t p1[2], p2[3];
   Double_t lsq, ssq, dx, dy, dpx, dpy, u;
   Double_t safe=1E30;
   Int_t isegmin=0;
   for (i1=0; i1<fNvert; i1++) {
      if (TGeoShape::IsSameWithinTolerance(safe,0)) {
         isegment = isegmin;
         return 0.;
      }
      i2 = (i1+1)%fNvert;
      p1[0] = fX[i1];
      p1[1] = fY[i1];
      p2[0] = fX[i2];
      p2[1] = fY[i2];

      dx = p2[0] - p1[0];
      dy = p2[1] - p1[1];
      dpx = point[0] - p1[0];
      dpy = point[1] - p1[1];

      lsq = dx*dx + dy*dy;
      if (TGeoShape::IsSameWithinTolerance(lsq,0)) {
         ssq = dpx*dpx + dpy*dpy;
         if (ssq < safe) {
            safe = ssq;
            isegmin = i1;
         }
         continue;
      }
      u = (dpx*dx + dpy*dy)/lsq;
      if (u>1) {
         dpx = point[0]-p2[0];
         dpy = point[1]-p2[1];
      } else {
         if (u>=0) {
            dpx -= u*dx;
            dpy -= u*dy;
         }
      }
      ssq = dpx*dpx + dpy*dpy;
      if (ssq < safe) {
         safe = ssq;
         isegmin = i1;
      }
   }
   isegment = isegmin;
   safe = TMath::Sqrt(safe);
//   printf("== segment %d: (%f, %f) - (%f, %f) safe=%f\n", isegment, fX[isegment],fY[isegment],fX[(isegment+1)%fNvert],fY[(isegment+1)%fNvert],safe);
   return safe;
}

////////////////////////////////////////////////////////////////////////////////
/// Sets the next polygone index. If index<0 sets all indices consecutive
/// in increasing order.

void TGeoPolygon::SetNextIndex(Int_t index)
{
   Int_t i;
   if (index <0) {
      for (i=0; i<fNvert; i++) fInd[i] = i;
      return;
   }
   if (fNconvex >= fNvert) {
      Error("SetNextIndex", "all indices already set");
      return;
   }
   fInd[fNconvex++] = index;
   if (fNconvex == fNvert) {
      if (!fX || !fY) return;
      Double_t area = 0.0;
      for (i=0; i<fNvert; i++) area += fX[fInd[i]]*fY[fInd[(i+1)%fNvert]]-fX[fInd[(i+1)%fNvert]]*fY[fInd[i]];
      if (area<0) TObject::SetBit(kGeoACW, kFALSE);
      else        TObject::SetBit(kGeoACW, kTRUE);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Set X/Y array pointer for the polygon and daughters.

void TGeoPolygon::SetXY(Double_t *x, Double_t *y)
{
   Int_t i;
   fX = x;
   fY = y;
   Double_t area = 0.0;
   for (i=0; i<fNvert; i++) area += fX[fInd[i]]*fY[fInd[(i+1)%fNvert]]-fX[fInd[(i+1)%fNvert]]*fY[fInd[i]];
   if (area<0) TObject::SetBit(kGeoACW, kFALSE);
   else        TObject::SetBit(kGeoACW, kTRUE);

   if (!fDaughters) return;
   TGeoPolygon *poly;
   Int_t nd = fDaughters->GetEntriesFast();
   for (i=0; i<nd; i++) {
      poly = (TGeoPolygon*)fDaughters->At(i);
      if (poly) poly->SetXY(x,y);
   }
}