How to let graphics primitives respond to a mouse click ?
This can be done by adding a TExec object in a TCanvas. The following macro gives an example.
It generates 50 small triangles randomly in the canvas. Each triangle get a unique identifier and a random color. Once this macro have been executed, clicking on any triangle shows a message giving the triangle identifier and its color.
void triangles(Int_t ntriangles=50) { TCanvas *c1 = new TCanvas("c1","triangles",10,10,700,700); TRandom r; Double_t dx = 0.2; Double_t dy = 0.2; Int_t ncolors = gStyle->GetNumberOfColors(); Double_t x[4],y[4]; for (Int_t i=0;i<ntriangles;i++) { x[0] = r.Uniform(.05,.95); y[0] = r.Uniform(.05,.95); x[1] = x[0] + dx*r.Rndm(); y[1] = y[0] + dy*r.Rndm(); x[2] = x[1] - dx*r.Rndm(); y[2] = y[1] - dy*r.Rndm(); x[3] = x[0]; y[3] = y[0]; TPolyLine *pl = new TPolyLine(4,x,y); pl->SetUniqueID(i); pl->SetFillColor(ncolors*r.Rndm()); pl->Draw("f"); } c1->AddExec("ex","TriangleClicked()"); } void TriangleClicked() { //this action function is called whenever you move the mouse //it just prints the id of the picked triangle //you can add graphics actions instead int event = gPad->GetEvent(); if (event != 11) return; //may be comment this line TObject *select = gPad->GetSelected(); if (!select) return; if (select->InheritsFrom("TPolyLine")) { TPolyLine *pl = (TPolyLine*)select; printf("You have clicked triangle %d, color=%d\n", pl->GetUniqueID(),pl->GetFillColor()); } }
