TGeoColorScheme Class Reference

Strategy object for assigning colors and transparency to geometry volumes.

Strategy class for assigning colors/transparency to geometry volumes.

This class is used by TGeoManager::DefaultColors(const TGeoColorScheme*) to assign visualization colors and transparency to geometry volumes, typically after GDML import where no color information is stored.

The default implementation combines:

• name-based material classification (e.g. metals, polymers, gases),
• a Z-binned fallback lookup when no name-based rule applies.

This class is intended for runtime use only (not persistified). Users can extend or override the default behavior by:

• installing hooks via std::function, or
• subclassing and overriding virtual methods.

See also

TGeoManager::DefaultColors

Helper "strategy" class used by TGeoManager::DefaultColors() to assign visualization attributes (line color and optional transparency) to imported geometries (e.g. GDML), where the source format does not encode colors.

Design goals

• Backward compatibility: calling TGeoManager::DefaultColors() with no arguments behaves like today (default "natural" scheme).
• Reasonable defaults for detector geometries: first try name-based material classification (e.g. copper, aluminium, steel, FR4/G10, kapton/polyimide, gases), then fall back to a Z-binned lookup.
• User extensibility without requiring subclassing: users can provide hooks (std::function) that override the default decisions partially or fully. Hooks are runtime-only (not persistified).

How TGeoManager::DefaultColors() uses a scheme

For each volume:

• scheme->Color(vol) is queried:
• return >= 0 : use returned ROOT color index (TColor index)
• return < 0 : caller may ignore or use its own fallback
• scheme->Transparency(vol) is queried:
• return in [0..100] : set volume transparency
• return < 0 : do not change transparency

Default behavior

• Color(vol):
• If a user color hook is installed, it is called first. If it returns >= 0, that color is used.
• Otherwise, try name-based overrides (tokens like "copper", "steel", "fr4", "g10", "kapton", "argon", "c6f14", ...).
• If still unresolved, fall back to ColorForZ(effectiveZ). Users can override the Z fallback via SetZFallbackHook() or by subclassing and overriding ColorForZ().
• Transparency(vol):
• If a user transparency hook is installed and returns >= 0, use it.
• Otherwise, the default makes very low-density materials (gases) semi-transparent (60), preserving historical behavior.

User extensibility examples

Example A: Tweak just copper-like materials (leave everything else default)

TGeoColorScheme cs(EGeoColorSet::kNatural);
cs.SetColorHook([](const TGeoVolume* v) -> Int_t {
  const TGeoMaterial* m = TGeoColorScheme::GetMaterial(v);
  if (!m || !m->GetName()) return -1;
  std::string n = m->GetName();
  std::transform(n.begin(), n.end(), n.begin(), ::tolower);
  if (n.find("copper") != std::string::npos || n.find("_cu") != std::string::npos)
    return TColor::GetColor(0.90f, 0.55f, 0.30f); // custom copper tint
  return -1; // let defaults handle the rest
});
gGeoManager->DefaultColors(&cs);

Example B: Override Z-fallback mapping (keep name overrides)

TGeoColorScheme cs(EGeoColorSet::kNatural);
cs.SetZFallbackHook([](Int_t Z, EGeoColorSet) -> Int_t {
  float t = std::min(1.f, std::max(0.f, Z / 100.f));
  return TColor::GetColor(t, t, t); // grayscale by Z
});
gGeoManager->DefaultColors(&cs);

Example C: Full custom policy via subclassing (optional)

class MyScheme : public TGeoColorScheme {
public:
  using TGeoColorScheme::TGeoColorScheme;
  Int_t ColorForZ(Int_t Z, EGeoColorSet set) const override { ... }
  Int_t Color(const TGeoVolume* vol) const override { ... }
};
MyScheme cs(EGeoColorSet::kFlashy);
gGeoManager->DefaultColors(&cs);

Notes

• This class is intended for runtime use; it is not persistified because hooks are user-provided callables which are not I/O friendly.
• The default name token rules are heuristic and aimed at typical HEP detector material naming conventions; users can refine them locally via hooks or subclassing.

See also

TGeoManager::DefaultColors

Definition at line 48 of file TGeoColorScheme.h.

Public Types
using	ColorHook_t = std::function<Int_t(const TGeoVolume *)>
	Type of user hook for overriding color assignment.
using	TranspHook_t = std::function<Int_t(const TGeoVolume *)>
	Type of user hook for overriding transparency assignment.
using	ZFallbackHook_t = std::function<Int_t(Int_t , EGeoColorSet )>
	Type of user hook for overriding the Z-based fallback coloring.

Public Member Functions
	TGeoColorScheme (EGeoColorSet set=EGeoColorSet::kNatural)
	Constructor.
virtual	~TGeoColorScheme ()
	Virtual destructor.
virtual Int_t	Color (const TGeoVolume *vol) const
	Compute the color for a given volume.
virtual Int_t	ColorForZ (Int_t Z, EGeoColorSet set) const
	Compute fallback color based on material effective Z.
EGeoColorSet	GetSet () const
	Get the active color set.
void	SetColorHook (ColorHook_t h)
	Set a user hook for color assignment.
void	SetSet (EGeoColorSet s)
	Set the active color set.
void	SetTransparencyHook (TranspHook_t h)
	Set a user hook for transparency assignment.
void	SetZFallbackHook (ZFallbackHook_t h)
	Set a user hook for Z-based fallback coloring.
virtual Int_t	Transparency (const TGeoVolume *vol) const
	Compute the transparency for a given volume.

Static Public Member Functions
static const TGeoMaterial *	GetMaterial (const TGeoVolume *vol)
	Retrieve the material associated with a geometry volume.

Private Attributes
ColorHook_t	fColorHook = nullptr
	Optional user hook for color assignment.
EGeoColorSet	fSet
	Active color set selection.
TranspHook_t	fTranspHook = nullptr
	Optional user hook for transparency.
ZFallbackHook_t	fZFallbackHook = nullptr
	Optional user hook for Z fallback.

#include <TGeoColorScheme.h>

Member Typedef Documentation

ColorHook_t

using TGeoColorScheme::ColorHook_t = std::function<Int_t(const TGeoVolume *)>

Type of user hook for overriding color assignment.

Definition at line 51 of file TGeoColorScheme.h.

TranspHook_t

using TGeoColorScheme::TranspHook_t = std::function<Int_t(const TGeoVolume *)>

Type of user hook for overriding transparency assignment.

Definition at line 54 of file TGeoColorScheme.h.

ZFallbackHook_t

using TGeoColorScheme::ZFallbackHook_t = std::function<Int_t(Int_t , EGeoColorSet )>

Type of user hook for overriding the Z-based fallback coloring.

Definition at line 57 of file TGeoColorScheme.h.

Constructor & Destructor Documentation

TGeoColorScheme()

TGeoColorScheme::TGeoColorScheme ( EGeoColorSet set = EGeoColorSet::kNatural )

explicit

Constructor.

Parameters

set	Initial color set selection (natural, flashy, high-contrast).

Definition at line 358 of file TGeoColorScheme.cxx.

~TGeoColorScheme()

TGeoColorScheme::~TGeoColorScheme ( )

virtualdefault

Virtual destructor.

Member Function Documentation

Color()

Int_t TGeoColorScheme::Color ( const TGeoVolume * vol ) const

virtual

Compute the color for a given volume.

This method is called by TGeoManager::DefaultColors() for each volume. The default implementation:

• calls the user color hook if installed,
• applies name-based material overrides,
• falls back to ColorForZ() if no rule matches.

Parameters

vol	Geometry volume to be colored.

Returns

ROOT color index (>=0) to apply, or <0 for "no decision".

See also

Transparency

ColorForZ

TGeoManager::DefaultColors

Definition at line 372 of file TGeoColorScheme.cxx.

ColorForZ()

Int_t TGeoColorScheme::ColorForZ ( Int_t Z, EGeoColorSet set ) const

virtual

Compute fallback color based on material effective Z.

This method is used when no name-based material override applies. Users may override this behavior via SetZFallbackHook() or by subclassing and overriding this method.

Parameters

Z	Effective atomic number of the material.
set	Active color set selection.

Returns

ROOT color index (>=0) to apply.

See also

SetZFallbackHook

Definition at line 420 of file TGeoColorScheme.cxx.

GetMaterial()

const TGeoMaterial * TGeoColorScheme::GetMaterial ( const TGeoVolume * vol )

static

Retrieve the material associated with a geometry volume.

This helper performs all necessary pointer checks and may be safely used inside user hooks.

Parameters

vol	Geometry volume.

Returns

Pointer to the associated material, or nullptr if unavailable.

Definition at line 362 of file TGeoColorScheme.cxx.

GetSet()

EGeoColorSet TGeoColorScheme::GetSet ( ) const

inline

Get the active color set.

Definition at line 154 of file TGeoColorScheme.h.

SetColorHook()

void TGeoColorScheme::SetColorHook ( ColorHook_t h )

inline

Set a user hook for color assignment.

The hook is called before any built-in logic. Returning a value <0 delegates the decision to the default implementation.

Parameters

h	Color hook (set to nullptr to disable).

See also

Color

Definition at line 127 of file TGeoColorScheme.h.

SetSet()

void TGeoColorScheme::SetSet ( EGeoColorSet s )

inline

Set the active color set.

Definition at line 157 of file TGeoColorScheme.h.

SetTransparencyHook()

void TGeoColorScheme::SetTransparencyHook ( TranspHook_t h )

inline

Set a user hook for transparency assignment.

The hook is called before the default transparency logic. Returning a value <0 delegates the decision to the default implementation.

Parameters

h	Transparency hook (set to nullptr to disable).

See also

Transparency

Definition at line 139 of file TGeoColorScheme.h.

SetZFallbackHook()

void TGeoColorScheme::SetZFallbackHook ( ZFallbackHook_t h )

inline

Set a user hook for Z-based fallback coloring.

The hook is called before the built-in Z-binned lookup. Returning a value <0 delegates the decision to the default implementation.

Parameters

h	Z-fallback hook (set to nullptr to disable).

See also

ColorForZ

Definition at line 151 of file TGeoColorScheme.h.

Transparency()

Int_t TGeoColorScheme::Transparency ( const TGeoVolume * vol ) const

virtual

Compute the transparency for a given volume.

The default implementation:

• calls the user transparency hook if installed,
• makes very low-density materials (e.g. gases) semi-transparent.

Parameters

vol	Geometry volume.

Returns

Transparency value in [0..100] to apply, or <0 to leave unchanged.

See also

Color

TGeoManager::DefaultColors

Definition at line 398 of file TGeoColorScheme.cxx.

Member Data Documentation

fColorHook

ColorHook_t TGeoColorScheme::fColorHook = nullptr

private

Optional user hook for color assignment.

Definition at line 173 of file TGeoColorScheme.h.

fSet

EGeoColorSet TGeoColorScheme::fSet

private

Active color set selection.

Definition at line 171 of file TGeoColorScheme.h.

fTranspHook

TranspHook_t TGeoColorScheme::fTranspHook = nullptr

private

Optional user hook for transparency.

Definition at line 174 of file TGeoColorScheme.h.

fZFallbackHook

ZFallbackHook_t TGeoColorScheme::fZFallbackHook = nullptr

private

Optional user hook for Z fallback.

Definition at line 175 of file TGeoColorScheme.h.

Libraries for TGeoColorScheme:

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The documentation for this class was generated from the following files:

• geom/geom/inc/TGeoColorScheme.h
• geom/geom/src/TGeoColorScheme.cxx