Can not move mouse on the second TGraph which called SetHighlight()

Crisps · July 18, 2024, 5:43am

Dear experts

I made a GUI to show waveform when the mouse is moving on the TGraph (event display), and I made 2 TGraph where the first one contains points that are not filtered, the second contains points that are filtered. Here is what I wrote:

//draw other things above
g1->SetMarkerColor(kBlue);
g2->SetMarkerColor(kBlue - 10);
g1->Draw("PSAME");
g2->Draw("PSAME");
g1->SetHighlight();
g2->SetHighlight();

I found that it’s nearly impossible to move my mouse on the points of the second TGraph, where the points on the first TGraph are very easy to be highlighted.
If I change the order like g2->SetHighlight(); g1->SetHighlight() this time the g1 becomes nearly impossible to be highlighted. How can I solve this?
(this problem is not fatal if number of points is small, but becomes fatal when I have many points near each other between 2 TGraph

Danilo · July 18, 2024, 8:16am

Hi,

Nice.
Adding in the loop a few experts who could help (@couet @bellenot @linev)

Cheers,
D

Crisps · July 22, 2024, 12:55pm

Any update…?

couet · July 22, 2024, 1:10pm

Can you send a small macro reproducing the problem?

Crisps · July 22, 2024, 1:41pm

void test(){
        TCanvas* c = new TCanvas();
        TGraph* g1 = new TGraph();
        TGraph* g2 = new TGraph();
        for(int i=0; i<50; ++i){
                for(int j = 0; j< 10; ++j){
                        double x1 = i;
                        double x2 = i + 0.5;
                        double y1 = j * 5;
                        double y2 = j * 5+ 3;
                        g1->AddPoint(x1, y1);
                        g2->AddPoint(x2, y2);
                }
        }
        g1->SetMarkerStyle(20);
        g2->SetMarkerStyle(20);
        g1->SetMarkerSize(0.4);
        g2->SetMarkerSize(0.4);
        g1->SetMarkerColor(kRed);
        g1->SetMarkerColor(kBlue);
        TH1F* frame = gPad->DrawFrame(0., 0., 50., 50.);
        frame->SetTitle("EventDisplay" );
        frame->GetXaxis()->SetTitle("X [mm]");
        frame->GetYaxis()->SetTitle("Y [mm]");
        TLine* l = new TLine(0, 25, 50, 25);
        g1->Draw("P");
        g2->Draw("P");
        g1->SetHighlight();
        g2->SetHighlight();
}

I found that g2 points that near Y=[15, 35] are hard to be highlighted.
If I Draw g2 first I found g1 hard to be highlighted.

couet · July 22, 2024, 1:55pm

I modified slightly your macro by adding the option L on the 2nd graph:

{
   TCanvas* c = new TCanvas();
   TGraph* g1 = new TGraph();
   TGraph* g2 = new TGraph();
   for(int i=0; i<50; ++i){
      for(int j = 0; j< 10; ++j){
         double x1 = i;
         double x2 = i + 0.5;
         double y1 = j * 5;
         double y2 = j * 5+ 3;
         g1->AddPoint(x1, y1);
         g2->AddPoint(x2, y2);
      }
   }
   g1->SetMarkerStyle(20);
   g2->SetMarkerStyle(20);
   g1->SetMarkerSize(0.4);
   g2->SetMarkerSize(0.4);
   g1->SetMarkerColor(kRed);
   g2->SetMarkerColor(kBlue);
   TH1F* frame = gPad->DrawFrame(0., 0., 50., 50.);
   frame->SetTitle("EventDisplay" );
   frame->GetXaxis()->SetTitle("X [mm]");
   frame->GetYaxis()->SetTitle("Y [mm]");
   TLine* l = new TLine(0, 25, 50, 25);
   g1->Draw("P");
   g2->Draw("PL");
}

As you can wee th plot because very crowded. The lines obscure the 1st plot. When you interact with a graph there is two way to manipulate it:

you click on a point they and hand is disokayed and ou can move that point
you click on a the line between 2 points (even if not displayed) then you can move the whole graph.

These two interaction modes are working perfectly with you example. It is just more tricky to pick the graph in the background but not impossible.

couet · July 22, 2024, 1:59pm

And if you draw both graphs with lines you see even better what I am taling about:

Crisps · July 22, 2024, 2:25pm

Yes, I can confirm that when I can not highlight the point it’s because the mouse is trying to move the graph (cursor changed to moving mode, becomes arrows)
Is there a way to disable the line between points, or disable the functionality that dragging the graph?

couet · July 22, 2024, 2:29pm

No, there is no way to disable the lines picking. It is hardcoded here:

github.com

root-project/root/blob/35dc9528fbc7bd861f5c9d5b818c95583296293c/hist/histpainter/src/TGraphPainter.cxx#L717


      
             }
          }
          
          
          ////////////////////////////////////////////////////////////////////////////////
          /// Compute distance from point px,py to a graph.
          ///
          /// Compute the closest distance of approach from point px,py to this line.
          /// The distance is computed in pixels units.
          
          Int_t TGraphPainter::DistancetoPrimitiveHelper(TGraph *theGraph, Int_t px, Int_t py)
          {
          
             // Are we on the axis?
             Int_t distance;
             if (theGraph->GetHistogram()) {
                distance = theGraph->GetHistogram()->DistancetoPrimitive(px,py);
                if (distance <= 5) return distance;
             }
          
             // Somewhere on the graph points?

Crisps · July 22, 2024, 2:37pm

Ah…I see .
Any suggestion for highlight a point that just stay behind a line of another graph? (like the issue I described, I can never point on a point sometimes…)

couet · July 23, 2024, 7:07am

Currently, there is no workaround for this issue. If a primitive is behind another, it cannot be accessed using the basic interaction provided by the canvas. In your case, the simplest solution might be to zoom in on the area you want to select so you can clearly differentiate between the two graphs.

ferhue · July 23, 2024, 8:57am

This macro solves the job for you:

#include <iostream>
#include "TPolyMarker.h"
#include "TMarker.h"
#include "TCanvas.h"
#include "TPad.h"
#include "TLine.h"
#include "TH1F.h"
#include "TMath.h"
#include "TClass.h"

TPolyMarker* g1 = nullptr;
TPolyMarker* g2 = nullptr;
TMarker* highl = nullptr;

using std::cout, std::endl;

void highlight(Int_t event, Int_t x, Int_t y, TObject *selected)
{
   TCanvas *c = (TCanvas *) gTQSender;
   //~ printf("Canvas %s: event=%d, xp=%d, yp=%d, selected=%s\n", c->GetName(),
          //~ event, x, y, selected->IsA()->GetName());
   const double d1 = g1->DistancetoPrimitive(x,y);
   const double d2 = g2->DistancetoPrimitive(x,y);
   const double d = std::min(d1,d2);
   const double threshold = 10; // in pixels
   if(d >= threshold) {
       delete highl;
       highl = nullptr;
       c->Modified();
       c->Update();
   }
   else
   {
       TPolyMarker* const gh = d1 < d2 ? g1 : g2;
       const Int_t np = gh->Size();
       Double_t * const px = gh->GetX();
       Double_t * const py = gh->GetY();
       Double_t mindist = 1e12;
       Int_t minidx = -1;
       for(Int_t i=0; i<np; ++i)
       {
           const double dist = TMath::Sqrt(TMath::Power(gPad->XtoAbsPixel(gPad->XtoPad(px[i]))-x,2)+TMath::Power(gPad->YtoAbsPixel(gPad->YtoPad(py[i]))-y,2));
           if(dist < mindist)
           {
               mindist = dist;
               minidx = i;
           }
       }
       if(!highl) {
        highl = new TMarker(px[minidx], py[minidx], 24);
        highl->SetBit(kCannotPick);
        highl->SetMarkerColor(gh->GetMarkerColor());
        highl->SetMarkerSize(gh->GetMarkerSize()*2.0);
        highl->Draw();
       }
       else {
           highl->SetMarkerColor(gh->GetMarkerColor());
           highl->SetMarkerSize(gh->GetMarkerSize()*2.0);
           highl->SetX(px[minidx]);
           highl->SetY(py[minidx]);
       }
       c->Modified();
       c->Update();
   }
}


void test(){
        TCanvas* c = new TCanvas();
        g1 = new TPolyMarker();
        g2 = new TPolyMarker();
        for(int i=0; i<50; ++i){
                for(int j = 0; j< 10; ++j){
                        double x1 = i;
                        double x2 = i + 0.5;
                        double y1 = j * 5;
                        double y2 = j * 5+ 3;
                        g1->SetNextPoint(x1, y1);
                        g2->SetNextPoint(x2, y2);
                }
        }
        g1->SetMarkerStyle(20);
        g2->SetMarkerStyle(20);
        g1->SetMarkerSize(0.4);
        g2->SetMarkerSize(0.4);
        g1->SetMarkerColor(kRed);
        g1->SetMarkerColor(kBlue);
        TH1F* frame = gPad->DrawFrame(0., 0., 50., 50.);
        frame->SetTitle("EventDisplay" );
        frame->GetXaxis()->SetTitle("X [mm]");
        frame->GetYaxis()->SetTitle("Y [mm]");
        TLine* l = new TLine(0, 25, 50, 25);
        g1->Draw("P");
        g2->Draw("P");
        //~ g1->SetHighlight();
        //~ g2->SetHighlight();
        c->Connect("ProcessedEvent(Int_t,Int_t,Int_t,TObject*)", nullptr, nullptr,
               "highlight(Int_t,Int_t,Int_t,TObject*)");
}