[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 fnx = 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

@@ -1171,8 +1171,13 @@ 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 +1377,11 @@ void TMultiGraph::Paint(Option_t *choptin)
       gfit->PaintStats(fit);
 }
 
-
 ////////////////////////////////////////////////////////////////////////////////
 /// Divides the active pad and draws all Graphs in the Multigraph separately.
+/// fnx 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 fnx)
 {
    if (!gPad) return;
 
@@ -1392,11 +1397,20 @@ 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 (fnx == 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 / fnx);
+         if (fnx * ny < neededPads)
+            ny++;
+         curPad->Divide(fnx, 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 x `m` rows of pads where `n` is given and `m` is calculated.|
 | "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 x `m` rows of pads where `n` is given and `m` is calculated.
 
 The following example shows various types of stacks (hist023_THStack_simple.C).