 ROOT   Reference Guide glvox2.C File Reference

## Detailed Description

This macro demonstrates how to use "glcol" option for TH3 and how to create user defined TRANSFER FUNCTION: transfer function maps bin value to voxel's opacity.

codomain is 0, 1 To pass transparency function into painting algorithm, you have to:

1. Create TF1 object (with symbolic expression like "0.5 * (sin(x) + 1)":
...
TF1 * tf = new TF1("TransferFunction", "0.5 * (sin(x) + 1)", -10., 10.);
...
1-Dim function class
Definition: TF1.h:213
IMPORTANT, the name of TF1 object MUST be "TransferFunction".
2. Add this function into a hist's list of functions:
...
TList * lof = hist->GetListOfFunctions();
...
It's also possible to use your own function and pass it into TF1, please read TF1 documentation to learn how.

This macro is to be compiled: TF1 is extremely slow with CINT's function as an argument. #include "TStyle.h"
#include "TList.h"
#include "TH3.h"
#include "TF1.h"
namespace {
Double_t my_transfer_function(const Double_t *x, const Double_t * /*param*/)
{
// Bin values in our example range from -2 to 1.
// Let's make values from -2. to -1.5 more transparent:
if (*x < -1.5)
return 0.08;
if (*x > -1.5 && *x < -0.5)
return 0.015;
if (*x < -0.5 && *x < 0.)
return 0.02;
if (*x > 0 && *x < 0.5)
return 0.03;
if (*x > 0.8)
return 0.01;
return 0.2;
}
}
void glvox2()
{
//Create and fill TH3.
const UInt_t nX = 30;
const Double_t xMin = -1., xMax = 1., xStep = (xMax - xMin) / (nX - 1);
const UInt_t nY = 30;
const Double_t yMin = -1., yMax = 1., yStep = (yMax - yMin) / (nY - 1);
const UInt_t nZ = 30;
const Double_t zMin = -1., zMax = 1., zStep = (zMax - zMin) / (nZ - 1);
TH3F *hist = new TH3F("glvoxel", "glvoxel", nX, -1., 1., nY, -1., 1., nZ, -1., 1.);
//Fill the histogram to create a "sphere".
for (UInt_t i = 0; i < nZ; ++i) {
const Double_t z = zMin + i * zStep;
for (UInt_t j = 0; j < nY; ++j) {
const Double_t y = yMin + j * yStep;
for (UInt_t k = 0; k < nX; ++k) {
const Double_t x = xMin + k * xStep;
const Double_t val = 1. - (x * x + y * y + z * z);
hist->SetBinContent(k + 1, j + 1, i + 1, val);
}
}
}
//Now, specify the transfer function.
TList * lf = hist->GetListOfFunctions();
if (lf) {
TF1 * tf = new TF1("TransferFunction", my_transfer_function);
}
hist->Draw("glcol");
}
unsigned int UInt_t
Definition: RtypesCore.h:46
double Double_t
Definition: RtypesCore.h:59
R__EXTERN TStyle * gStyle
Definition: TStyle.h:413
TList * GetListOfFunctions() const
Definition: TH1.h:243
virtual void Draw(Option_t *option="")
Draw this histogram with options.
Definition: TH1.cxx:3074
3-D histogram with a float per channel (see TH1 documentation)}
Definition: TH3.h:268
virtual void SetBinContent(Int_t bin, Double_t content)
Set bin content.
Definition: TH3.cxx:3388