[hist] Allow to customize pads layout for THStack and TMultiGraph

hist/hist/inc/TMultiGraph.h

@@ -73,7 +73,7 @@ class TMultiGraph : public TNamed {
    TAxis            *GetXaxis();
    TAxis            *GetYaxis();
    void              Paint(Option_t *chopt = "") override;
-   void              PaintPads(Option_t *chopt = "");
+   void              PaintPads(Option_t *chopt = "", Int_t nColumn = 0);
    void              PaintPolyLine3D(Option_t *chopt = "");
    void              PaintReverse(Option_t *chopt = "");
    void              Print(Option_t *chopt="") const override;

hist/hist/src/THStack.cxx

@@ -759,10 +759,18 @@ void THStack::BuildAndPaint(Option_t *choptin, Bool_t paint, Bool_t rebuild_stac
       lclear = kFALSE;
       opt.ReplaceAll("noclear","");
    }
-   if (opt.Contains("pads")) {
+   auto l = strstr(opt.Data(), "pads");
+   if (l) {
       if (!paint)
          return;
 
+      Int_t fnx = 0;
+      if (sscanf(&l[4], "%d", &fnx) > 0) {
+         opt.ReplaceAll(TString::Format("pads%d", fnx), "");
+      } else {
+         opt.ReplaceAll("pads", "");
+      }
+
       Int_t npads = fHists->GetSize();
       TVirtualPad *padsav = gPad;
       //if pad is not already divided into subpads, divide it
@@ -773,12 +781,21 @@ void THStack::BuildAndPaint(Option_t *choptin, Bool_t paint, Bool_t rebuild_stac
             nps++;
       }
       if (nps < npads) {
-         padsav->Clear();
-         Int_t nx = (Int_t)TMath::Sqrt((Double_t)npads);
-         if (nx*nx < npads) nx++;
-         Int_t ny = nx;
-         if (((nx*ny)-nx) >= npads) ny--;
-         padsav->Divide(nx,ny);
+         if (fnx <= 0) {
+            padsav->Clear();
+            Int_t nx = (Int_t)TMath::Sqrt((Double_t)npads);
+            if (nx * nx < npads)
+               nx++;
+            Int_t ny = nx;
+            if (((nx * ny) - nx) >= npads)
+               ny--;
+            padsav->Divide(nx, ny);
+         } else {
+            Int_t ny = (Int_t)((Double_t)npads / fnx);
+            if (fnx * ny < npads)
+               ny++;
+            padsav->Divide(fnx, ny);
+         }
       }
 
       Int_t i = 1;

hist/hist/src/TMultiGraph.cxx

@@ -46,9 +46,10 @@ extern void H1LeastSquareSeqnd(Int_t n, Double_t *a, Int_t idim, Int_t &ifail, I
     - [Setting drawing options](\ref MG01a)
     - [Titles setting](\ref MG01b)
     - [The option \"3D\"](\ref MG01c)
-    - [Legend drawing](\ref MG01d)
-    - [Automatic coloring](\ref MG01e)
-    - [Reverse axis](\ref MG01f)
+    - [Options \"PADS\" and \"PADSn\"](\ref MG01d)
+    - [Legend drawing](\ref MG01e)
+    - [Automatic coloring](\ref MG01f)
+    - [Reverse axis](\ref MG01g)
 - [MultiGraphs' fitting](\ref MG02)
     - [Fit box position](\ref MG02a)
 - [Axis' limits setting](\ref MG03)
@@ -155,6 +156,53 @@ Begin_Macro(source)
 End_Macro
 
 \anchor MG01d
+#### Options "PADS" and "PADSn"
+
+Like for THStack, options `PADS` and `PADSn` to split drawing into individual pads for each graph are also available.
+
+| Option     | Description                                                     |
+|------------|-----------------------------------------------------------------|
+| "PADS"     | The current pad/canvas is subdivided into a number of pads equal to the number of graphs in the multigraph and each graph is paint into a separate pad.|
+| "PADSn"    | Like PADS but the current pad/canvas is subdivided into `n` columns, automatically calculating the number of rows.|
+
+Begin_Macro(source)
+{
+auto c0 = new TCanvas("c1","multigraph L3",200,10,700,500);
+
+auto mg = new TMultiGraph();
+
+auto gr1 = new TGraph(); gr1->SetLineColor(kBlue);
+auto gr2 = new TGraph(); gr2->SetLineColor(kRed);
+auto gr3 = new TGraph(); gr3->SetLineColor(kGreen);
+auto gr4 = new TGraph(); gr4->SetLineColor(kOrange);
+
+Double_t dx = 6.28/1000;
+Double_t x  = -3.14;
+
+for (int i=0; i<=1000; i++) {
+    x = x+dx;
+    gr1->SetPoint(i,x,2.*TMath::Sin(x));
+    gr2->SetPoint(i,x,TMath::Cos(x));
+    gr3->SetPoint(i,x,TMath::Cos(x*x));
+    gr4->SetPoint(i,x,TMath::Cos(x*x*x));
+    }
+
+    mg->Add(gr4); gr4->SetTitle("Cos(x*x*x)"); gr4->SetLineWidth(3);
+    mg->Add(gr3); gr3->SetTitle("Cos(x*x)")  ; gr3->SetLineWidth(3);
+    mg->Add(gr2); gr2->SetTitle("Cos(x)")    ; gr2->SetLineWidth(3);
+    mg->Add(gr1); gr1->SetTitle("2*Sin(x)")  ; gr1->SetLineWidth(3);
+
+    mg->SetTitle("Multi-graph Title; X-axis Title; Y-axis Title");
+
+    mg->Draw("a fb l pads3");
+
+    mg->GetHistogram()->GetXaxis()->SetRangeUser(0.,2.5);
+    gPad->Modified();
+    gPad->Update();
+}
+End_Macro
+
+\anchor MG01e
 #### Legend drawing
 
 The method TPad::BuildLegend is able to extract the graphs inside a
@@ -216,7 +264,7 @@ Begin_Macro(source)
 }
 End_Macro
 
-\anchor MG01e
+\anchor MG01f
 #### Automatic coloring
 
 Automatic coloring according to the current palette is available as shown in the
@@ -226,7 +274,7 @@ Begin_Macro(source)
 ../../../tutorials/visualisation/graphs/gr105_multigraphpalettecolor.C
 End_Macro
 
-\anchor MG01f
+\anchor MG01g
 #### Reverse axis
 
 \since **ROOT version 6.19/02**
@@ -1171,8 +1219,13 @@ void TMultiGraph::Paint(Option_t *choptin)
 
    l = strstr(chopt.Data(),"PADS");
    if (l) {
-      chopt.ReplaceAll("PADS","");
-      PaintPads(chopt.Data());
+      Int_t fnx = 0;
+      if (sscanf(&l[4], "%d", &fnx) > 0) {
+         chopt.ReplaceAll(TString::Format("PADS%d", fnx), "");
+      } else {
+         chopt.ReplaceAll("PADS", "");
+      }
+      PaintPads(chopt.Data(), fnx);
       return;
    }
 
@@ -1372,11 +1425,11 @@ void TMultiGraph::Paint(Option_t *choptin)
       gfit->PaintStats(fit);
 }
 
-
 ////////////////////////////////////////////////////////////////////////////////
 /// Divides the active pad and draws all Graphs in the Multigraph separately.
+/// nColumn parameter larger than 0 enforces number of columns for pad division
 
-void TMultiGraph::PaintPads(Option_t *option)
+void TMultiGraph::PaintPads(Option_t *option, Int_t nColumn)
 {
    if (!gPad) return;
 
@@ -1392,11 +1445,20 @@ void TMultiGraph::PaintPads(Option_t *option)
    }
    if (existingPads < neededPads) {
       curPad->Clear();
-      Int_t nx = (Int_t)TMath::Sqrt((Double_t)neededPads);
-      if (nx*nx < neededPads) nx++;
-      Int_t ny = nx;
-      if (((nx*ny)-nx) >= neededPads) ny--;
-      curPad->Divide(nx,ny);
+      if (nColumn <= 0) {
+         Int_t nx = (Int_t)TMath::Sqrt((Double_t)neededPads);
+         if (nx * nx < neededPads)
+            nx++;
+         Int_t ny = nx;
+         if (((nx * ny) - nx) >= neededPads)
+            ny--;
+         curPad->Divide(nx, ny);
+      } else {
+         Int_t ny = (Int_t)((Double_t)neededPads / nColumn);
+         if (nColumn * ny < neededPads)
+            ny++;
+         curPad->Divide(nColumn, ny);
+      }
    }
    Int_t i = 0;
 

hist/histpainter/src/THistPainter.cxx

@@ -355,6 +355,7 @@ using `TH1::GetOption`:
 | "NOSTACK"  | Histograms in the stack are all paint in the same pad as if the option `SAME` had been specified.|
 | "NOSTACKB" | Histograms are  drawn next to each other as bar charts.|
 | "PADS"     | The current pad/canvas is subdivided into a number of pads equal to the number of histograms in the stack and each histogram is paint into a separate pad.|
+| "PADSn"    | Like PADS but the current pad/canvas is subdivided into a `n` columns, automatically calculating the number of rows.|
 | "PFC"      | Palette Fill Color: stack's fill color is taken in the current palette. |
 | "PLC"      | Palette Line Color: stack's line color is taken in the current palette. |
 | "PMC"      | Palette Marker Color: stack's marker color is taken in the current palette. |
@@ -2751,9 +2752,10 @@ the same pad as if the option `SAME` had been specified. This allows to
 compute X and Y scales common to all the histograms, like
 `TMultiGraph` does for graphs.
 
-If the option `PADS` is specified, the current pad/canvas is
-subdivided into a number of pads equal to the number of histograms and each
-histogram is paint into a separate pad.
+If the option `PADS` is specified, the current pad/canvas is subdivided into
+a number of pads equal to the number of histograms and each histogram is paint
+into a separate pad. With `PADSn`, the current pad/canvas is subdivided into
+`n` columns, automatically calculating the number of rows.
 
 The following example shows various types of stacks (hist023_THStack_simple.C).