JLegend.hh

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#ifndef __JROOT__JLEGEND__
#define __JROOT__JLEGEND__

#include <string>

#include "TLegend.h"
#include "TPad.h"
#include "TStyle.h"


/**
 * \author mdejong
 */

namespace JROOT {}
namespace JPP { using namespace JROOT; }

namespace JROOT {

  /**
   * Get legend.
   *
   * \param  width        width    [characters]
   * \param  height       height   [lines]
   * \param  option       position [TR TL BL BR]
   * \param  factor       factor font size
   * \return              legend
   */
  inline TLegend* getLegend(const Int_t       width,
                            const Int_t       height,
                            const std::string option,
                            const Double_t    factor = 1.0)
  {
    using namespace std;
      
    gPad->Update();

    const Double_t X1  = 0.0 + gPad->GetLeftMargin();
    const Double_t X2  = 1.0 - gPad->GetRightMargin();
    const Double_t Y1  = 0.0 + gPad->GetBottomMargin();
    const Double_t Y2  = 1.0 - gPad->GetTopMargin();

    const Double_t w   = gPad->XtoPixel(gPad->GetX2());
    const Double_t h   = gPad->YtoPixel(gPad->GetY1());

    const Double_t w1  = fabs(gPad->XtoPixel(gPad->GetX2()) - gPad->XtoPixel(gPad->GetX1()));
    const Double_t h1  = fabs(gPad->YtoPixel(gPad->GetY2()) - gPad->YtoPixel(gPad->GetY1()));

    const Double_t mw  = 2.0;                                  // extra width
    const Double_t mh  = 0.5;                                  // extra height
    const Double_t eps = 0.005;                                // extra space [NDC]
    const Double_t ts  = gStyle->GetStatFontSize() * factor;   // text size   [NDC]
    const Double_t ch  = ts * (w < h ? w : h);                 // text size   [pixel]

    Double_t W  = (width  + mw) * (ch/w1) * factor;            // width  [NDC]
    Double_t H  = (height + mh) * (ch/h1) * factor;            // height [NDC]

    Double_t fc = 1.0;                                         // extra scaling factor

    if (fc * W > X2 - X1 - 2*eps) { fc *= (X2 - X1 - 2*eps) / W; }
    if (fc * H > Y2 - Y1 - 2*eps) { fc *= (Y2 - Y1 - 2*eps) / H; }

    W  *= fc;
    H  *= fc;
    
    // default position is top-right

    Double_t x1  = X2 - W - eps;
    Double_t y1  = Y2 - H - eps;
    Double_t x2  = X2     - eps;
    Double_t y2  = Y2     - eps;

    if (option.find('T') != string::npos && option.find('B') == string::npos) {   // top
      y1  = Y2 - H - eps;
      y2  = Y2     - eps;
    }

    if (option.find('B') != string::npos && option.find('T') == string::npos) {   // bottom
      y1  = Y1     + eps;
      y2  = Y1 + H + eps;
    }

    if (option.find('R') != string::npos && option.find('L') == string::npos) {   // right
      x1  = X2 - W - eps;
      x2  = X2     - eps;
    }

    if (option.find('L') != string::npos && option.find('R') == string::npos) {   // left
      x1  = X1     + eps;
      x2  = X1 + W + eps;
    }
    
    TLegend* lg = new TLegend(x1, y1, x2, y2);

    //lg->SetFillStyle(4000);
    lg->SetFillColor(kWhite);
    lg->SetBorderSize(0);
    lg->SetTextAlign(12);
    lg->SetTextFont(gStyle->GetStatFont());
    lg->SetTextSize(ts);

    return lg;
  }
}

#endif