[hist3d] avoid paint of extremly small segments

On some platforms FindVisibleDraw returns
different result for same data.
Either line is not visible at all or extremly small
segment from the line is visible.
In last case do not call paint for gPad

Has effect on 3D axis grid painter and lego painter for
several stressGraphics tests - but only when checking
PS/SVG/PDF content, size reduction is very small

Author: linev

hist/histpainter/src/TPainter3dAlgorithms.cxx

@@ -43,6 +43,7 @@ class by Rene Brun.
 const Double_t kRad  = TMath::ATan(1)*Double_t(4)/Double_t(180);
 const Double_t kFdel = 0.;
 const Double_t kDel  = 0.0001;
+const Double_t kEps  = 1e-9; // exclude such small segments
 const Int_t kNiso  = 4;
 const Int_t kNmaxp = kNiso*13;
 const Int_t kNmaxt = kNiso*12;
@@ -593,7 +594,8 @@ void TPainter3dAlgorithms::DrawFaceMove1(Int_t *icodes, Double_t *xyz, Int_t np,
          y[0] = p1[1] + ydel*fT[2*it + 0];
          x[1] = p1[0] + xdel*fT[2*it + 1];
          y[1] = p1[1] + ydel*fT[2*it + 1];
-         gPad->PaintPolyLine(2, x, y);
+         if (TMath::Abs(fT[2*it + 0] - fT[2*it + 1]) > kEps)
+            gPad->PaintPolyLine(2, x, y);
       }
    }
 
@@ -621,7 +623,8 @@ void TPainter3dAlgorithms::DrawFaceMove1(Int_t *icodes, Double_t *xyz, Int_t np,
          y[0] = p1[1] + ydel*fT[2*it + 0];
          x[1] = p1[0] + xdel*fT[2*it + 1];
          y[1] = p1[1] + ydel*fT[2*it + 1];
-         gPad->PaintPolyLine(2, x, y);
+         if (TMath::Abs(fT[2*it + 0] - fT[2*it + 1]) > kEps)
+            gPad->PaintPolyLine(2, x, y);
       }
    }
 
@@ -681,7 +684,8 @@ void TPainter3dAlgorithms::DrawFaceMove2(Int_t *icodes, Double_t *xyz, Int_t np,
          y[0] = p1[1] + ydel*fT[2*it + 0];
          x[1] = p1[0] + xdel*fT[2*it + 1];
          y[1] = p1[1] + ydel*fT[2*it + 1];
-         gPad->PaintPolyLine(2, x, y);
+         if (TMath::Abs(fT[2*it + 0] - fT[2*it + 1]) > kEps)
+            gPad->PaintPolyLine(2, x, y);
       }
    }
 
@@ -763,7 +767,8 @@ void TPainter3dAlgorithms::DrawFaceMove3(Int_t *icodes, Double_t *xyz, Int_t np,
             y[0] = p1[1] + ydel*fT[2*it + 0];
             x[1] = p1[0] + xdel*fT[2*it + 1];
             y[1] = p1[1] + ydel*fT[2*it + 1];
-            gPad->PaintPolyLine(2, x, y);
+            if (TMath::Abs(fT[2*it + 0] - fT[2*it + 1]) > kEps)
+               gPad->PaintPolyLine(2, x, y);
          }
       }
    }