// Create a new color palette with colors ranging
// from blue (low) to red (high).
//
// How it works:
// We have to assign a new color palette to the global
// instance of TStyle called gStyle.
// This palette is simply an array of integers which hold
// the color ID for the referring level.
// In ROOT colors are created through TColor where they also
// get their ID assigned.
// ROOT reserves all colors below 50 and above 100.
// Here we restrict ourselves to the 50 IDs from 51 to 100.
//
// The color model used here is based on the HLS model which
// is much more suitable for creating palettes than RGB.
// Fixing the saturation and lightness we can scan through the
// spectrum of visible light by using "hue" alone.
// In Root hue takes values from 0 to 360.
//
// Problems: Often it is not possible to allocate a new color.
// This is especially true in X11. ROOT unfortunately gives no
// direct information on the success of TColor. There is however
// a workaround which is used here and shall not be explained
// in detail. If we fail to allocate one color we simply use the
// last successfully allocated color.
// This makes the macro independent of the graphics package and
// the underlying hardware.
//
void palette()
{
const float saturation = 1;
const float lightness = 0.5;
const float MaxHue = 280;
const float MinHue = 0;
const int MaxColors = 50;
int palette[MaxColors];
int index;
float hue, r, g, b, rv, gv, bv;
TColor *color;
unsigned int failures = 0;
for (int i=0 ; i<MaxColors ; i++) {
index = palette[i] = MaxColors+1+i;
color = new TColor(index, 0, 0, 0);
hue = MaxHue-(i+1)*((MaxHue-MinHue)/MaxColors);
color->HLStoRGB(hue, lightness, saturation, r, g, b);
color->SetRGB(r, g, b);
gGXW->GetRGB(index, rv, gv, bv);
if (r != rv || g != gv || b != bv) {
failures++;
palette[i] = i ? palette[i-1] : 1;
}
}
if (failures)
printf("palette(): couldn't allocate %d of %d colors\n", failures, MaxColors);
gStyle->SetPalette(MaxColors, palette);
}
//
// The following macro will produce an example figure
//
int main()
{
gROOT->Reset();
palette(); // Call The Palette Function
TCanvas *c1 = new TCanvas("c1","Spectrum Palette",200,10,900,500);
c1->Divide(2,1);
// Generate a 2-D function
TF2 *f2 = new TF2("f2","exp( -5.*(x^2+y^2)^(1/2))*cos((x^2+y^2)^(1/2)*10.0) ",-1.0,1.0,-1.0,1.0); // Example graph
//The following calls are important to set up the color scheme for the 'f2' calls.
f2->SetContour(48); // This is needed to use all 50 colors. (If above 48 it will cycle through color map).
f2->SetFillColor(0); // If using a histogram it is not nessesary.
c1->cd(1);
f2->Draw("SURF1");
c1->cd(2);
f2->Draw("COLZ");
return 0;
}