TGraph not accepting gStyle->Palette

Newbie
,
1

Hi everyone,

I would like to fill a TGraph polygon with a color from a specified gStyle->Palette(), as in the short example below. The problem seems to be that when I change the Palette() from default to e.g. Viridis, my graph line and fill colors don’t change. I tried with plotting option “f” and “pfc”, in TGraph and in TH1D, in Root versions 6.24 and 6.22 .

Apologies if this problem has an obvious solution that I am missing. Thanks in advance.

grTest
grTest698×475 2.34 KB 

gStyle->SetPalette(kViridis);
TCanvas *c2 = new TCanvas("grTest");
c2->cd();
double x[5] = {1., 3., 3., 1., 1.};
double y[5] = {1., 1., 2., 2., 1.};
TGraph* grTest = new TGraph(5, x, y);
grTest->SetTitle("grTest");
grTest->SetFillColor(3);
grTest->SetFillStyle(1001);
grTest->SetLineColor(2);
grTest->SetLineWidth(6);
grTest->Draw("al f");
//grTest->Draw("al pfc");
TImage *img = TImage::Create();
img->FromPad(c2);
img->WriteImage("grTest.png");
delete img;

Please read tips for efficient and successful posting and posting code

ROOT Version: 6.22 and 6.24
Platform: Ubuntu and Redhat
Compiler: cint only

2

Try adding the “fill” option (F) too:

 grTest->Draw("A L F PFC");
3

The TGraph plotting never use the palette.
What do you expect ? you have 5 points connected by a line. How the palette should be used ? I have no idea.

4

I tried “A L F PFC” and was still not able to get the graph to acknowledge gStyle->SetPalette(). I was able to change the fill style with grTest->SetFillStyle(3201), below.

I am trying to depict energy depositions into crystals with a color heat-map. Each crystal is represented as a polygon (rectangle defined by 5 points). The polygon gets filled with a color if it gets hit in my simulation. It would be great if the color could show how much energy got deposited into the crystal.

image
image698×475 4.1 KB

5

Hi @slocum ,
do I understand correctly that you want to change grTest->SetFillColor(3) in your original snippet to grTest->SetFillColor(ColorFromPaletteForValue(intensity)); where intensity can be, say, from 0 to 100 and ColorFromPaletteForValue should return a different color depending on intensity selecting it from a color palette?

If that’s the case, see the example using TColor::CreateGradientColorTable() here: ROOT: TColor Class Reference .

6

Hi @eguiraud , yes that is exactly what I was trying to do. And, I was able to find a solution using the link that you suggested. Thank you very much! The working code snippet is below.

image
image698×475 2.31 KB 

int ci = TColor::GetFreeColorIndex();
TColor *color = new TColor(ci, 0.8, 0.9, 0.9);  // arbitrary numbers
int palette[1] = {ci};
gStyle->SetPalette(1,palette);

TCanvas *c2 = new TCanvas("grTest");
c2->cd();
double x[5] = {1., 3., 3., 1., 1.};
double y[5] = {1., 1., 2., 2., 1.};
TGraph* grTest = new TGraph(5, x, y);
grTest->SetTitle("grTest");
grTest->Draw("ap f pfc");
TImage *img = TImage::Create();
img->FromPad(c2);
img->WriteImage("grTest.png");
delete img;