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"# triangles\n",
" \\preview Create small triangles at random positions on the canvas.\n",
"Assign a unique ID to each triangle, and give each one a random color from the color palette.\n",
"\n",
"```cpp\n",
"root > .x triangles.C\n",
"```\n",
"\n",
"When a triangle is clicked, a message displaying its unique number and color will be printed.\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Rene Brun \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:37 PM."
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" Definition of a helper function: "
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"%%cpp -d\n",
"void TriangleClicked()\n",
"{\n",
" // this action function is called whenever you move the mouse\n",
" // it just prints the id of the picked triangle\n",
" // you can add graphics actions instead\n",
" int event = gPad->GetEvent();\n",
" if (event != 11)\n",
" return; // may be comment this line\n",
" TObject *select = gPad->GetSelected();\n",
" if (!select)\n",
" return;\n",
" if (select->InheritsFrom(TPolyLine::Class())) {\n",
" TPolyLine *pl = (TPolyLine *)select;\n",
" printf(\"You have clicked triangle %d, color=%d\\n\", pl->GetUniqueID(), pl->GetFillColor());\n",
" }\n",
"}"
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" Arguments are defined. "
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"int ntriangles = 50;"
]
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"auto c1 = new TCanvas(\"c1\", \"triangles\", 10, 10, 700, 700);\n",
"gStyle->SetPalette(kCMYK);\n",
"TRandom r;\n",
"double dx = 0.2;\n",
"double dy = 0.2;\n",
"int ncolors = TColor::GetNumberOfColors();\n",
"double x[4], y[4];\n",
"for (int i = 0; i < ntriangles; i++) {\n",
" x[0] = r.Uniform(.05, .95);\n",
" y[0] = r.Uniform(.05, .95);\n",
" x[1] = x[0] + dx * r.Rndm();\n",
" y[1] = y[0] + dy * r.Rndm();\n",
" x[2] = x[1] - dx * r.Rndm();\n",
" y[2] = y[1] - dy * r.Rndm();\n",
" x[3] = x[0];\n",
" y[3] = y[0];\n",
" auto pl = new TPolyLine(4, x, y);\n",
" pl->SetUniqueID(i);\n",
" int ci = ncolors * r.Rndm();\n",
" TColor *c = gROOT->GetColor(TColor::GetColorPalette(ci));\n",
" c->SetAlpha(r.Rndm());\n",
" pl->SetFillColor(c->GetNumber());\n",
" pl->Draw(\"f\");\n",
"}\n",
"c1->AddExec(\"ex\", \"TriangleClicked()\");"
]
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"Draw all canvases "
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