void xtruSamples()
{
   // One normally specifies the x-y points in counter-clockwise order;
   // flip this to TRUE to test that it doesn't matter.
   Bool_t makecw = kFALSE;

   // One normally specifies the z points in increasing z order;
   // flip this to TRUE to test that it doesn't matter.
   Bool_t reversez = kFALSE;

   // One shouldn't be creating malformed polygons
   // but to test what happens when one does here's a flag.
   // The effect will be only apparent in solid rendering mode
   Bool_t domalformed = kFALSE;
   //  domalformed = kTRUE;

   TCanvas *c1 = new TCanvas("c1", "sample TXTRU Shapes", 200, 10, 640, 640);

   // Create a new geometry
   TGeometry *geom = new TGeometry("sample", "sample");
   geom->cd();

   // Define the complexity of the drawing
   Int_t zseg = 6;     // either 2 or 6
   Int_t extravis = 0; // make extra z "arrow" visible

   Float_t unit = 1;

   // Create a large BRIK to embed things into
   Float_t bigdim = 12.5 * unit;
   TBRIK *world = new TBRIK("world", "world", "void", bigdim, bigdim, bigdim);

   // Create the main node, make it invisible
   TNode *worldnode = new TNode("worldnode", "world node", world);
   worldnode->SetVisibility(0);
   worldnode->cd();

   // Canonical shape ... gets further modified by scale factors
   // to create convex (and malformed) versions
   Float_t x[] = {-0.50, -1.20, 1.20, 0.50, 0.50, 1.20, -1.20, -0.50};
   Float_t y[] = {-0.75, -2.00, -2.00, -0.75, 0.75, 2.00, 2.00, 0.75};
   Float_t z[] = {-0.50, -1.50, -1.50, 1.50, 1.50, 0.50};
   Float_t s[] = {0.50, 1.00, 1.50, 1.50, 1.00, 0.50};
   Int_t nxy = sizeof(x) / sizeof(Float_t);
   Float_t convexscale[] = {7.0, -1.0, 1.5};

   Int_t icolor[] = {1, 2, 3, 2, 2, 2, 4, 2, 6};

   // xycase and zcase:  0=convex, 1=malformed, 2=concave
   // this will either create a 2x2 matrix of shapes
   // or a 3x3 array (if displaying malformed versions)
   for (Int_t zcase = 0; zcase < 3; zcase++) {
      if (zcase == 1 && !domalformed)
         continue;
      for (Int_t xycase = 0; xycase < 3; xycase++) {
         if (xycase == 1 && !domalformed)
            continue;

         char name[9];
         sprintf(name, "txtru%1d%1d%1d", xycase, zcase, zseg);
         TXTRU *mytxtru = new TXTRU(name, name, "void", 8, 2);

         Int_t i, j;
         Float_t xsign = (makecw) ? -1 : 1;
         Float_t zsign = (reversez) ? -1 : 1;

         // set the vertex points
         for (i = 0; i < nxy; i++) {
            Float_t xtmp = x[i] * xsign;
            Float_t ytmp = y[i];
            if (i == 0 || i == 3 || i == 4 || i == 7)
               xtmp *= convexscale[xycase];
            if (xycase == 2)
               xtmp *= 2;
            mytxtru->DefineVertex(i, xtmp, ytmp);
         }
         // set the z segment positions and scales
         for (i = 0, j = 0; i < zseg; i++) {
            Float_t ztmp = z[i] * zsign;
            if (i == 0 || i == 5)
               ztmp *= convexscale[zcase];
            if (zcase == 2)
               ztmp *= 2.5;
            if (zseg > 2 && zcase != 2 && (i == 1 || i == 4))
               continue;
            mytxtru->DefineSection(j, ztmp, s[i]);
            j++;
         }

         TNode *txtrunode = new TNode(name, name, mytxtru);
         txtrunode->SetLineColor(icolor[3 * zcase + xycase]);
         Float_t pos_scale = (domalformed) ? 10 : 6;
         Float_t xpos = (xycase - 1) * pos_scale * unit;
         Float_t ypos = (zcase - 1) * pos_scale * unit;
         txtrunode->SetPosition(xpos, ypos, 0.);
      }
   }

   // Some extra shapes to show the direction of "z"
   Float_t zhalf = 0.5 * bigdim;
   Float_t rmax = 0.03 * bigdim;
   TCONE *zcone = new TCONE("zcone", "zcone", "void", zhalf, 0., rmax, 0., 0.);
   zcone->SetVisibility(extravis);
   TNode *zconenode = new TNode("zconenode", "zconenode", zcone);
   zconenode->SetLineColor(3);

   Float_t dzstub = 2 * rmax;
   TBRIK *zbrik = new TBRIK("zbrik", "zbrik", "void", rmax, rmax, dzstub);
   zbrik->SetVisibility(extravis);
   TNode *zbriknode = new TNode("zbriknode", "zbriknode", zbrik);
   zbriknode->SetPosition(0., 0., zhalf + dzstub);
   zbriknode->SetLineColor(3);

   //  geom->ls();

   geom->Draw();

   // Tweak the pad so that it displays the entire geometry undistorted
   TVirtualPad *thisPad = gPad;
   if (thisPad) {
      TView *view = thisPad->GetView();
      if (!view)
         return;
      Double_t min[3], max[3], center[3];
      view->GetRange(min, max);
      int i;
      // Find the boxed center
      for (i = 0; i < 3; i++)
         center[i] = 0.5 * (max[i] + min[i]);
      Double_t maxSide = 0;
      // Find the largest side
      for (i = 0; i < 3; i++)
         maxSide = TMath::Max(maxSide, max[i] - center[i]);
   file: // Adjust scales:
      for (i = 0; i < 3; i++) {
         max[i] = center[i] + maxSide;
         min[i] = center[i] - maxSide;
      }
      view->SetRange(min, max);
      thisPad->Modified();
      thisPad->Update();
   }
}