TPie - avoid circle stretching

ROOT
1

Hi!

I’m playing a bit with TPie(s).
I noticed that if I the canvas width and height differ, the pie is not a circle but an ellipsis.
Is there a way to maintain the circle as a circle even when they differ?

Just to give an example:

void pc()
{
	Float_t vals[] = {.2,1.1,.6,.9,2.3};
	Int_t colors[] = {2,3,4,5,6};
	Int_t nvals = sizeof(vals)/sizeof(vals[0]);

	TCanvas *cpie = new TCanvas("cpie","TPie test",700,400);
	TPie *pie4 = new TPie("pie4","Pie with verbose labels",nvals,vals,colors);
	pie4->SetCircle(0.40, 0.5, 0.30);
	pie4->Draw("nol");
	TLegend *legend = pie4->MakeLegend();
	legend->SetX1(0.82);
	legend->SetX2(0.98);
	legend->SetY1(0.75);
	legend->SetY2(0.9);
}

This macro produces a pie which is actually an ellipsis.

If you wonder why I am asking this: I want to save the output picture and not having to edit that using some picture editor software in order to trim the unneeded white area.

Thank you!

2

One solution would be to keep a fixed canvas size:

TCanvas *c1 = new TCanvas("c1","c1");
c1->SetCanvasSize(1500, 1500);

Then, when resizing the Windows, you will get scrollbars. Another solution would be to react to every window resize and recompute the drawing, but this is more complex…

3

Uhm…
I’d like to save the output picture without having to edit/resize/whatever.
That means that the root macro that I’m currently writing will end with a c->SaveAs(“whatever.gif”).

4

Well, then c1->SetCanvasSize(1500, 1500); is the right solution

5

Indeed, the point is: how to let the user change the canvas shape without affecting the shape of the pie itself! :slight_smile:
I don’t want square canvas because then I had to trim the extra&unneeded&unwanted white areas.

6

Then create a square TPad inside the rectangle Canvas

7

May I ask you some help with this?
I’ve never used TPads. I don’t know how to tell root to draw the Pie on that, and not on the canvas.

8

Maybe there is a simpler solution. Could you try with TCanvas::SetFixedAspectRatio()?

9

Here we go:

void pc()
{
	Float_t vals[] = {.2,1.1,.6,.9,2.3};
	Int_t colors[] = {2,3,4,5,6};
	Int_t nvals = sizeof(vals)/sizeof(vals[0]);

	TCanvas *cpie = new TCanvas("cpie","TPie test",700,400);
	cpie->SetFixedAspectRatio(kTRUE);
	TPad *pad = new TPad("pad", "pad", 0.2142857, 0., 0.7857142857, 1.0);
	pad->Draw();
	pad->cd();
	TPie *pie4 = new TPie("pie4","Pie with verbose labels",nvals,vals,colors);
	pie4->SetCircle(0.40, 0.5, 0.30);
	pie4->Draw("nol");
	TLegend *legend = pie4->MakeLegend();
	legend->SetX1(0.82);
	legend->SetX2(0.98);
	legend->SetY1(0.75);
	legend->SetY2(0.9);
}
1 Like
10 
{
  Float_t vals[] = {.2,1.1,.6,.9,2.3};
  Int_t colors[] = {2,3,4,5,6};
  Int_t nvals = sizeof(vals)/sizeof(vals[0]);
  
  TCanvas *cpie = new TCanvas("cpie","TPie test",700,400);
  // cpie->SetFixedAspectRatio(kTRUE); // only if needed
  // create a square sub-pad
  Double_t ratio = (double)cpie->GetWw() / (double)cpie->GetWh();
  TPad *square;
  if (ratio > 1.) square = new TPad("square", "square", 0., 0., 1. / ratio, 1.);
  else square = new TPad("square", "square", 0., 0., 1., ratio);
  square->Draw();
  square->cd(); // switch to the square sub-pad
  // draw the pie in the square sub-pad
  TPie *pie4 = new TPie("pie4","Pie with verbose labels",nvals,vals,colors);
  pie4->SetCircle(0.40, 0.5, 0.30);
  pie4->Draw("nol");
  cpie->cd(0); // return to the main pad
  // draw the legend in the main pad
  TLegend *legend = pie4->MakeLegend();
  legend->SetX1(0.82);
  legend->SetX2(0.98);
  legend->SetY1(0.75);
  legend->SetY2(0.9);
}
1 Like
11

So it’s just about “cd” to the pad I want to use.

Thank you both for your help. :slight_smile:

12

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