Class TLogicalRgb

TLogicalRgb

Support

Supported from 6.0

Description

Provides support for system colours, in addition to literal colours, in text formatting.

The base class TRgb stores the 24-bit literal colour value using a TUint32. TLogicalRgb uses the unused (top) byte as an 8-bit index. The purpose of the index is to allow applications to use logical colours. If the index is zero, the value is not a logical colour; it is treated as an ordinary TRgb value. If the index is non zero (1-255), the colour should be translated by the application into a system colour. Indices 254 and 255 are reserved for the system foreground and background colours, respectively and should be translated into them. Translation from index to RGB colour occurs in the implementation of MFormParam::SystemColor().

All colours in the Text and text attributes API are stored using TLogicalRgb values and are initialised to either TLogicalRgb::ESystemForegroundColor or TLogicalRgb::ESystemBackgroundColor.

This system allows an application to set its text colours once, perhaps using the system-wide colour scheme, rather than having to set the colours each time a text object is created. It is also compatible with legacy code which expects TRgb rather than TLogicalRgb values — for example, the logical foreground and background colours have their bottom three bytes filled with black and white respectively so that code which expects TRgb values can still use them.

Derivation

TLogicalRgb Provides support for system colours, in addition to literal colours, in text formatting TRgb 24-bit RGB colour value with 8 bits each for red, green and blue

Defined in TLogicalRgb:
Anonymous, ESystemBackgroundColor, ESystemBackgroundIndex, ESystemForegroundColor, ESystemForegroundIndex, SetSystemColorIndex(), SystemColorIndex(), TLogicalRgb(), TSystemColor

Inherited from TRgb:
Blue(), Color16(), Color16M(), Color256(), Color4K(), Color64K(), Difference(), ExternalizeL(), Gray16(), Gray2(), Gray256(), Gray4(), Green(), InternalizeL(), Red(), SetBlue(), SetGreen(), SetRed(), Value(), operator!=(), operator&(), operator&=(), operator==(), operator^(), operator^=(), operator|(), operator|=(), operator~()

TLogicalRgb()

Description

Allows an uninitialised object to be constructed.

TLogicalRgb(TUint32 aValue)

Description

Constructs the object with a 32-bit integer. The index is stored in the top byte. A TRgb value may be stored in the bottom three bytes.

Parameters

TUint32 aValue Integer holding the logical colour index.

TLogicalRgb(TSystemColor aValue)

Description

Constructs the object with a TSystemColor value.

Parameters

TSystemColor aValue Identifies whether the colour is the system foreground or system background colour.

TLogicalRgb(const TRgb& aRgb)

Description

Constructs a new TLogicalRgb object from an existing one.

TUint SystemColorIndex() const

Description

Returns the logical colour's index value. Zero indicates that the value is not a logical colour; it is an ordinary TRgb value. 254 and 255 indicate the system foreground and background colours, respectively.

Return value

TUint The index: between zero and 255 inclusive.

void SetSystemColorIndex(TUint aIndex)

Description

Sets the logical colour's index value.

Parameters

TUint aIndex The new index value (between 1 and 253 inclusive).

Anonymous

Description

Miscellaneous constants.

ESystemForegroundIndex Index reserved for the system foreground colour (=254). ESystemBackgroundIndex Index reserved for the system background colour (=255).

TSystemColor

Description

Used to construct TLogicalRgb objects which should use either the system foreground or background colour.

ESystemForegroundColor The system foreground colour. ESystemBackgroundColor The system background colour.