Logo ROOT   6.21/01
Reference Guide
grad.C File Reference

Detailed Description

This macro demonstrates how to create and use linear gradients to fill a histogram or a pad.

To use this macro you need OpenGL enabled in pad: either set OpenGL.CanvasPreferGL to 1 in $ROOTSYS/etc/system.rootrc; or call gStyle->SetCanvasPreferGL(kTRUE); before canvas created.

pict1_grad.C.png
//Includes for ACLiC (cling does not need them).
#include "TColorGradient.h"
#include "TCanvas.h"
#include "TColor.h"
#include "TStyle.h"
#include "TError.h"
#include "TH1F.h"
//Aux. functions for tutorials/gl.
#include "customcolorgl.h"
//______________________________________________________________________
void grad()
{
//1. Try to 'allocate' five indices for our custom colors.
//We can use hard-coded indices like 1001, 1002, 1003, ... but
//I prefer to find free indices in the ROOT's color table
//to avoid possible conflicts with other tutorials.
Color_t colorIndices[5] = {};
::Error("grad", "failed to create new custom colors");
return;
}
//Make sure we enabled OpenGL support in a canvas.
//2. Test if canvas supports OpenGL:
TCanvas * const cnv = new TCanvas("gradient demo 1", "gradient demo 1", 100, 100, 600, 600);
if (!cnv->UseGL()) {
::Error("grad", "This macro requires OpenGL");
delete cnv;
return;
}
typedef TColorGradient::Point Point;
//3. Create custom 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.
const Color_t &frameGradient = colorIndices[2];//This gradient is a mixture of colorIndices[0] and colorIndices[1]
//Fill color for a pad frame:
{
new TColor(colorIndices[0], 0.25, 0.25, 0.25, "special pad color1", 0.55);
new TColor(colorIndices[1], 1., 1., 1., "special pad color2", 0.05);
//dark-white-white-dark:
const Double_t locations[] = {0., 0.2, 0.8, 1.};
const Color_t gradientIndices[4] = {colorIndices[0], colorIndices[1], colorIndices[1], colorIndices[0]};
//Gradient for a pad's frame.
TLinearGradient * const gradFill1 = new TLinearGradient(frameGradient, 4, locations, gradientIndices);
//Horizontal:
gradFill1->SetStartEnd(Point(0., 0.), Point(1., 0.));
}
//This gradient is a mixture of two standard colors.
const Color_t &padGradient = colorIndices[3];
//Fill color for a pad:
{
const Double_t locations[] = {0., 1.};
const Color_t gradientIndices[4] = {30, 38};//We create a gradient from system colors.
//Gradient for a pad.
TLinearGradient * const gradFill2 = new TLinearGradient(padGradient, 2, locations, gradientIndices);
//Vertical:
gradFill2->SetStartEnd(Point(0., 0.), Point(0., 1.));
}
//Another gradient built from three standard colors.
const Color_t &histGradient = colorIndices[4];
//Fill color for a histogram:
{
const Color_t gradientIndices[3] = {kYellow, kOrange, kRed};
const Double_t locations[3] = {0., 0.5, 1.};
//Gradient for a histogram.
TLinearGradient * const gradFill3 = new TLinearGradient(histGradient, 3, locations, gradientIndices);
//Vertical:
gradFill3->SetStartEnd(Point(0., 0.), Point(0., 1.));
}
cnv->SetFillColor(padGradient);
cnv->SetFrameFillColor(frameGradient);
TH1F * const hist = new TH1F("a1", "b1", 20, -3., 3.);
hist->SetFillColor(histGradient);
hist->FillRandom("gaus", 100000);
hist->Draw();
}
Author
Timur Pocheptsov

Definition in file grad.C.