Issue using TColor and saving canvas to ROOT format

[ttedeschi]

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Description

It seems that when saving a canvas to a ROOT file (SaveAs("c.root")), colors defined with TColor::GetColor are not preserved whereas builtin colors are. This can be seen saving the canvas to both . png .root formats, then load the .root and save it again as a .png, and compare the two pngs created.

Tagging CMS CAT conveners @lenzip @anigamova and DPROC subconveners @oglez @ttedeschi

Reproducer

Define a save.C macro:

{
  TRandom3 r;
  TH1F h = TH1F("test","Test",100,-1.0,1.0);
  for (int i=0;i<=1000;++i) {
    h.Fill(r.Rndm());
  }

  TCanvas c = TCanvas();
  c.Draw();

  h.SetFillStyle(1001);
  h.SetFillColor(TColor::GetColor("#F5BB54"));

  //h.SetFillColor(kRed);
  h.Draw("HIST");

  c.SaveAs("c.root");
  c.SaveAs("c.png");
}

and a load.C macro:

{
TFile *f = new TFile("c.root");
TH1F *h1 = (TH1F*)f->Get("c1");
h1->Draw();
h1->SaveAs("loaded_c.png")
}

If h.SetFillColor(TColor::GetColor("#F5BB54")); is uncommented and h.SetFillColor(kRed) is commented, c.png and loaded_c.png differ (the latter lacks the color), whereas if h.SetFillColor(TColor::GetColor("#F5BB54")) is commented and h.SetFillColor(kRed) is uncommented, c.png and loaded_c.png are the same (both properly showing the red fill color).

ROOT version

6.32.04

Installation method

Docker image

Operating system

Ubuntu 24.04⁠

Additional context

No response

[couet]

Yes, this is how the colors are implemented. Only the builtins colors are known at saving time in root files. This other formats save the colors (including .C).

[linev]

One can store all colors in the canvas if call TColor::DefinedColors(1) before.
If read such canvas back - all colors (including custom) will be restored.

[linev]

@ttedeschi

Did you try to call TColor::DefinedColors(1) before storing canvas in ROOT file?

[ttedeschi]

Hi sorry for the late reply, I tried and it works for ROOT 6.32 (I am finally able to see the right color in the loaded canvas), while with ROOT 6.30 I get

/test/./load_new.C:6:18: error: use 'template' keyword to treat 'Get' as a dependent template name
auto cnv = file->Get<TCanvas>("c1");
                 ^
                 template 
/test/./load_new.C:6:1: error: Syntax error
auto cnv = file->Get<TCanvas>("c1");
^
FunctionDecl 0x5af6325fe230 <input_line_8:1:1, /test/./load_new.C:14:1> input_line_8:1:6 __cling_Un1Qu30 'void (void *)'
|-ParmVarDecl 0x5af6325fe178 <col:22, col:28> col:28 vpClingValue 'void *'
|-CompoundStmt 0x5af6326e1a70 <col:42, /test/./load_new.C:14:1>
| |-DeclStmt 0x5af6326de478 <line:3:1, col:35>
| | `-VarDecl 0x5af63264d6a8 <col:1, col:34> col:8 f 'TFile *' cinit
| |   `-CXXNewExpr 0x5af6326de418 <col:12, col:34> 'TFile *' CXXMethod 0x5af6326db188 'operator new' 'void *(size_t)'
| |     `-CXXConstructExpr 0x5af6326ddee0 <col:16, col:34> 'TFile':'TFile' 'void (const char *, Option_t *, const char *, Int_t)'
| |       |-ImplicitCastExpr 0x5af6326dde68 <col:22> 'const char *' <ArrayToPointerDecay>
| |       | `-StringLiteral 0x5af63264d788 <col:22> 'const char[11]' lvalue "c_new.root"
| |       |-CXXDefaultArgExpr 0x5af6326dde80 <<invalid sloc>> 'const char *'
| |       |-CXXDefaultArgExpr 0x5af6326ddea0 <<invalid sloc>> 'const char *'
| |       `-CXXDefaultArgExpr 0x5af6326ddec0 <<invalid sloc>> 'Int_t':'int'
| |-DeclStmt 0x5af6326df820 <line:6:1, col:36>
| | `-VarDecl 0x5af6326de508 <col:1, col:35> col:6 used cnv 'auto' cinit
| |   `-CallExpr 0x5af6326df7c8 <col:12, col:35> '<dependent type>'
| |     |-CXXDependentScopeMemberExpr 0x5af6326df6b0 <col:12, col:29> '<dependent type>' lvalue ->Get
| |     | `-DeclRefExpr 0x5af6326de680 <col:12> '<dependent type>' lvalue Var 0x5af6326de578 'file' '<dependent type>'
| |     `-StringLiteral 0x5af6326df7a8 <col:31> 'const char[3]' lvalue "c1"
| |-CallExpr 0x5af6326df8c0 <line:8:1, col:11> '<dependent type>'
| | `-CXXDependentScopeMemberExpr 0x5af6326df878 <col:1, col:6> '<dependent type>' lvalue ->Draw
| |   `-DeclRefExpr 0x5af6326df838 <col:1> 'auto' lvalue Var 0x5af6326de508 'cnv' 'auto'
| |-CallExpr 0x5af6326e1a40 <line:10:1, col:31> '<dependent type>'
| | |-CXXDependentScopeMemberExpr 0x5af6326df900 <col:1, col:6> '<dependent type>' lvalue ->SaveAs
| | | `-DeclRefExpr 0x5af6326df8e0 <col:1> 'auto' lvalue Var 0x5af6326de508 'cnv' 'auto'
| | `-StringLiteral 0x5af6326e1a18 <col:13> 'const char[17]' lvalue "loaded_c_new.png"
| `-NullStmt 0x5af6326e1a68 <line:13:1>
|-AnnotateAttr 0x5af6326de5e0 <<invalid sloc>> Implicit R"ATTRDUMP(__ResolveAtRuntime)ATTRDUMP"
`-AnnotateAttr 0x5af6326de730 <<invalid sloc>> Implicit R"ATTRDUMP(__ResolveAtRuntime)ATTRDUMP"
<<<NULL>>>

p.s. just for completeness I made a little mistake in the example above, I load the object in the root file as an histogram, but I would have to load it as a canvas object.. anyway if I substitute TH1F *h1 = (TH1F*)f->Get("c1"); with auto cnv = f->Get<TCanvas>("c1"); the issue is exactly the same

[linev]

Looks like you need to use latest ROOT version to get desired functionality.