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

Detailed Description

This tutorial demonstrates how to use radial gradients, custom colors, transparency.

Requires OpenGL: either set OpenGL.CanvasPreferGL to 1 in the $ROOTSYS/etc/system.rootrc, or use gStyle->SetCanvasPreferGL(kTRUE).

pict1_radialgradients.C.png
//Includes for ACLiC:
#include <cassert>
#include <cstdlib>
#include "TColorGradient.h"
#include "TEllipse.h"
#include "TRandom.h"
#include "TCanvas.h"
#include "TStyle.h"
#include "TError.h"
//Aux. functions.
#include "customcolorgl.h"
namespace {
//Just some colors (rgba) to build our
//fancy gradients from.
const Double_t basicColors[][4] =
{
{1., 0., 0., 1.},
{1., 0.3, 0., 1.},
{0., 0., 1., 1.},
{1., 1., 0., 1.},
{1., 0., 1., 1.},
{0., 1., 1., 1.},
{0., 1., 0., 1.},
{0., 0.5, 0., 1.},
//transparent colors:
{1., 0., 0., 0.5},
{1., 0.3, 0., 0.5},
{0., 0., 1., 0.5},
{1., 1., 0., 0.5},
{1., 0., 1., 0.5},
{0., 1., 1., 0.5},
{0., 1., 0., 0.5},
{0., 0.5, 0., 0.5},
//and even more transparent:
{1., 0., 0., 0.2},
{1., 0.3, 0., 0.2},
{0., 0., 1., 0.2},
{1., 1., 0., 0.2},
{1., 0., 1., 0.2},
{0., 1., 1., 0.2},
{0., 1., 0., 0.2},
{0., 0.5, 0., 0.2}
};
const unsigned nBasicColors = sizeof basicColors / sizeof basicColors[0];
//______________________________________________________________________
Color_t CreateRandomGradientFill()
{
const Double_t * const fromRGBA = basicColors[(std::rand() % (nBasicColors / 2))];
//With odd number of colors the last one is never selected :)
const Double_t * const toRGBA = basicColors[nBasicColors / 2 + (std::rand() % (nBasicColors / 2))];
const Double_t locations[] = {0., 1.};
const Double_t rgbas[] = {fromRGBA[0], fromRGBA[1], fromRGBA[2], fromRGBA[3],
toRGBA[0], toRGBA[1], toRGBA[2], toRGBA[3]};
Color_t idx[1] = {};
return -1;
TRadialGradient * const grad = new TRadialGradient(idx[0], 2, locations, rgbas);
//
return idx[0];
}
//______________________________________________________________________
bool add_ellipse(const Double_t xC, const Double_t yC, const Double_t r)
{
assert(gPad != nullptr && "add_ellipse, no pad to add ellipse");
const Color_t newColor = CreateRandomGradientFill();
if (newColor == -1) {
::Error("add_ellipse", "failed to find a new color index for a gradient fill");
return false;
}
TEllipse * const newEllipse = new TEllipse(xC, yC, r, r);
newEllipse->SetFillColor(newColor);
newEllipse->Draw();
return true;
}
}
//______________________________________________________________________
void radialgradients()
{
gRandom->SetSeed(4357);//;)
TCanvas * const cnv = new TCanvas("radial gradients", "radial gradients", 800, 800);
if (!cnv->UseGL()) {
::Error("radialgradients", "this demo OpenGL");
delete cnv;
return;
}
for (unsigned i = 0; i < 100; ++i)
if (!add_ellipse(gRandom->Rndm(), gRandom->Rndm(), 0.5 * gRandom->Rndm()))
break;
cnv->Modified();
cnv->Update();
}
Author
Timur Pocheptsov

Definition in file radialgradients.C.