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"# hist105_TExec_dynamic_slice\n",
"Example of function called when a mouse event occurs in a pad.\n",
"When moving the mouse in the canvas, a second canvas shows the\n",
"projection along X of the bin corresponding to the Y position\n",
"of the mouse. The resulting histogram is fitted with a gaussian.\n",
"A \"dynamic\" line shows the current bin position in Y.\n",
"This more elaborated example can be used as a starting point\n",
"to develop more powerful interactive applications exploiting CINT\n",
"as a development engine.\n",
"\n",
"Note that a class is used to hold on to the canvas that display\n",
"the selected slice.\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Rene Brun, Johann Cohen-Tanugi, Wim Lavrijsen, Enric Tejedor \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:13 PM."
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"import sys\n",
"import ctypes\n",
"\n",
"from ROOT import gRandom, gPad, gROOT, gVirtualX\n",
"from ROOT import kTRUE, kRed\n",
"from ROOT import TCanvas, TH2, TH2F\n",
"\n",
"\n",
"class DynamicExec:\n",
"\n",
" def __init__( self ):\n",
" self._cX = None\n",
" self._cY = None\n",
" self._old = None\n",
"\n",
" def __call__( self ):\n",
"\n",
" h = gPad.GetSelected();\n",
" if not h:\n",
" return\n",
"\n",
" if not isinstance( h, TH2 ):\n",
" return\n",
"\n",
" gPad.GetCanvas().FeedbackMode( kTRUE )\n",
"\n",
" # erase old position and draw a line at current position\n",
" px = gPad.GetEventX()\n",
" py = gPad.GetEventY()\n",
"\n",
" uxmin, uxmax = gPad.GetUxmin(), gPad.GetUxmax()\n",
" uymin, uymax = gPad.GetUymin(), gPad.GetUymax()\n",
" pxmin, pxmax = gPad.XtoAbsPixel( uxmin ), gPad.XtoAbsPixel( uxmax )\n",
" pymin, pymax = gPad.YtoAbsPixel( uymin ), gPad.YtoAbsPixel( uymax )\n",
"\n",
" if self._old != None:\n",
" gVirtualX.DrawLine( pxmin, self._old[1], pxmax, self._old[1] )\n",
" gVirtualX.DrawLine( self._old[0], pymin, self._old[0], pymax )\n",
" gVirtualX.DrawLine( pxmin, py, pxmax, py )\n",
" gVirtualX.DrawLine( px, pymin, px, pymax )\n",
"\n",
" self._old = px, py\n",
"\n",
" upx = gPad.AbsPixeltoX( px )\n",
" x = gPad.PadtoX( upx )\n",
" upy = gPad.AbsPixeltoY( py )\n",
" y = gPad.PadtoY( upy )\n",
"\n",
" padsav = gPad\n",
"\n",
" # create or set the display canvases\n",
" if not self._cX:\n",
" self._cX = TCanvas( 'c2', 'Projection Canvas in X', 730, 10, 700, 500 )\n",
" else:\n",
" self._DestroyPrimitive( 'X' )\n",
"\n",
" if not self._cY:\n",
" self._cY = TCanvas( 'c3', 'Projection Canvas in Y', 10, 550, 700, 500 )\n",
" else:\n",
" self._DestroyPrimitive( 'Y' )\n",
"\n",
" self.DrawSlice( h, y, 'Y' )\n",
" self.DrawSlice( h, x, 'X' )\n",
"\n",
" padsav.cd()\n",
"\n",
" def _DestroyPrimitive( self, xy ):\n",
" proj = getattr( self, '_c'+xy ).GetPrimitive( 'Projection '+xy )\n",
" if proj:\n",
" proj.IsA().Destructor( proj )\n",
"\n",
" def DrawSlice( self, histo, value, xy ):\n",
" yx = xy == 'X' and 'Y' or 'X'\n",
"\n",
" # draw slice corresponding to mouse position\n",
" canvas = getattr( self, '_c'+xy )\n",
" canvas.SetGrid()\n",
" canvas.cd()\n",
"\n",
" bin = getattr( histo, 'Get%saxis' % xy )().FindBin( value )\n",
" hp = getattr( histo, 'Projection' + yx )( '', bin, bin )\n",
" hp.SetFillColor( 38 )\n",
" hp.SetName( 'Projection ' + xy )\n",
" hp.SetTitle( xy + 'Projection of bin=%d' % bin )\n",
" hp.Fit( 'gaus', 'ql' )\n",
" hp.GetFunction( 'gaus' ).SetLineColor( kRed )\n",
" hp.GetFunction( 'gaus' ).SetLineWidth( 6 )\n",
" canvas.Update()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" # create a new canvas.\n",
" c1 = TCanvas('c1', 'Dynamic Slice Example', 10, 10, 700, 500 )\n",
" c1.SetFillColor( 42 )\n",
" c1.SetFrameFillColor( 33 )\n",
"\n",
" # create a 2-d histogram, fill and draw it\n",
" hpxpy = TH2F( 'hpxpy', 'py vs px', 40, -4, 4, 40, -4, 4 )\n",
" hpxpy.SetStats( 0 )\n",
" x, y = ctypes.c_double( 0.1 ), ctypes.c_double( 0.101 )\n",
" for i in range( 50000 ):\n",
" # pass ctypes doubles by reference, then retrieve their modified values with .value\n",
" gRandom.Rannor( x, y )\n",
" hpxpy.Fill( x.value, y.value )\n",
" hpxpy.Draw( 'COL' )\n",
"\n",
" # Add a TExec object to the canvas (explicit use of __main__ is for IPython)\n",
" import __main__\n",
" __main__.slicer = DynamicExec()\n",
" c1.AddExec( 'dynamic', 'TPython::Exec( \"slicer()\" );' )\n",
" c1.Update()"
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"Draw all canvases "
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"source": [
"from ROOT import gROOT \n",
"gROOT.GetListOfCanvases().Draw()"
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