gradients.C

Go to the documentation of this file.

/// \file
/// \ingroup tutorial_gl
/// Features:
///  1. Radial and linear gradients
///  2. Transparent/semitransparent colours.
///
/// \macro_image(nobatch)
/// \macro_code
///
/// \authors  Timur Pocheptsov, Sergey Linev
 
//Includes for ACLiC:
#include "TColorGradient.h"
#include "TCanvas.h"
#include "TError.h"
#include "TStyle.h"
#include "TText.h"
#include "TPie.h"
 
 
void gradients(bool gl = true)
{
   //Find free colour indices in the ROOT's palette for:
   //1. A radial gradient for TPie;
   //2. A linear gradient for TCanvas
   //3. A fully transparent fill color for a nested pad.
 
   gStyle->SetCanvasPreferGL(gl);
 
   auto c = new TCanvas("cpie","Gradient colours demo", 700, 700);
   //Before we allocated any new colour or created any object:
   if (!c->UseGL() && !c->IsWeb())
      ::Warning("gradients", "This macro requires either OpenGL or Web canvas to correctly handle gradient colors");
 
   //Linear gradient is defined by: 1) colors (to interpolate between them),
   //2) coordinates for these colors along the gradient axis [0., 1.] (must be sorted!).
   //3) Start and end points for a gradient, you specify them in some NDC rect ([0,0 - 1,1]),
   //and this rect is either: bounding rect of your polygon/object to fill
   //(gradient->SetCoordinateMode(TColorGradient::kObjectBoundingMode))
   //or bounding rect of a pad (gradient->SetCoordinateMode(TColorGradient::kPadMode)).
   //kObjectBoundingMode is the default one.
 
 
   //Draw a text in the canvas (the object above the text will be
   //semi-transparent):
   auto t = new TText(0.05, 0.7, "Can you see the text?");
   t->Draw();
 
   //We create a nested pad on top to render a TPie in,
   //this way we still have a text (below) + TPie with
   //a fancy colour on top.
   auto pad = new TPad("p", "p", 0., 0., 1., 1.);
 
   //TPad itself is fully transparent:
   auto transparentFill = TColor::GetColor((Float_t) 1., 1., 1., 0.);
   pad->SetFillColor(transparentFill);
   //Add our pad into the canvas:
   pad->Draw();
   pad->cd();
 
 
   //Radial gradient fill for a TPie object:
   auto col3 = TColor::GetColor((Float_t) 1., 0.8, 0., 1.); /*opaque orange at the start:*/
   auto col4 = TColor::GetColor((Float_t) 1., 0.2, 0., 0.65); /*transparent red at the end:*/
 
   //'Simple' radial gradient with radius 0.4
   auto radialFill = TColor::GetRadialGradient(0.4, {col3, col4});
 
 
   //Linear gradient fill (with an axis angle == 45):
   auto col1 = TColor::GetColor((Float_t) 0.2, 0.2, 0.2); /*gray*/
   auto col2 = TColor::GetColor((Float_t) 0.8, 1., 0.9); /*pale green*/
   auto linearFill = TColor::GetLinearGradient(45., {col1, col2}); //45 degrees:
 
   //Set as a background color in the canvas:
   c->SetFillColor(linearFill);
 
 
   const UInt_t nSlices = 5;
   //Values for a TPie (non-const, that's how TPie's ctor is declared):
   Double_t values[nSlices] = {0.8, 1.2, 1.2, 0.8, 1.};
   Int_t colors[nSlices] = {radialFill, radialFill, radialFill,
                            radialFill, radialFill};
 
   TPie * const pie = new TPie("pie", "TPie:", nSlices, values, colors);
   //One slice is slightly shifted:
   pie->SetEntryRadiusOffset(2, 0.05);
   //Move labels to the center (to fit the pad's space):
   pie->SetLabelsOffset(-0.08);
   //
   pie->SetRadius(0.4);
   pie->Draw("rsc");
}