Class CPalette

CPalette

Support

Supported from 6.1

Description

Provides user-definable palette support to the GDI.

A palette is a user-defined set of colours, which is a subset of the full range of 24-bit colours. This allows users the advantages of having a low bpp colour mode whilst being able to specify the colours available in that mode. To give an example, the EColor16 mode provides a palette of 16 colours as it provides a mapping between an integer index and a TRgb colour (see the table EGA Low-colour constants). Only a palette of 16 colour enables you to change the palette. Palettes are also used to allow 24-bit bitmaps to be stored in a more compressed form by finding the actual number of different colours used in the bitmap, creating a palette to allow the mapping of these colours to a smaller index space, and encoding the bitmap’s pixels using indexes to this new index space.

A palette has a size which is set at its creation and cannot be altered — the number of entries in the palette. Each entry in a palette is a mapping between that entry’s index and a TRgb value. Palette entries can be got and set at any time between the palette’s creation and destruction. The GDI’s palette support also provides functions to find the nearest palette colour to a requested TRgb colour.

Derivation

CBase Base class for all classes to be instantiated on the heap CPalette Provides user-definable palette support to the GDI

Defined in CPalette:
Clear(), Entries(), GetDataPtr(), GetEntry(), NearestEntry(), NearestIndex(), NewDefaultL(), NewL(), SetEntry(), ~CPalette()

Inherited from CBase:
operator new()

static CPalette* NewL(TInt aNumberOfEntries);

Description

Creates a new palette of the specified number of entries.

Parameters

TInt aNumberOfEntries The number of entries in the palette being created.

Return value

CPalette* The newly created palette.

static CPalette* NewDefaultL(TDisplayMode aDispMode);

Description

Creates a new default palette for the specified display mode. The default palette for a particular display mode has one entry for each possible colour in that display mode (4 entries for EGray2, 256 entries for EColor16 etc.); the colour of each index p in the default palette is set to its default value according to its display mode (e.g. if the mode is EColor16 then palette[p]=Color16(p); if the mode is EGray4 then palette[p]=Gray4(p)).

Parameters

TDisplayMode aDispMode The display mode for which the palette is to be created.

Return value

CPalette* The newly created palette

~CPalette();

Description

Destructor.

void Clear();

Description

Clears all the entries in the palette to TRgb(0).

void GetDataPtr(TInt aFirstColor,TInt aNumColors,TPtr8& aPtr);

Description

Returns a descriptor over the palette entries for the specifed colors. It is designed so that the descriptor can be passed to another thread and that thread copy the relevant entries.

Parameters

TInt aFirstColor The first colour. TInt aNumColors Number of colours. TPtr8& aPtr Descriptor.

TInt Entries() const;

Description

Gets the number of entries in the palette

Return value

TInt The number of entries in the palette.

TRgb GetEntry(TInt aPaletteIndex) const;

Description

Gets the rgb value of the palette entry aPaletteIndex.

Parameters

TInt aPaletteIndex The index of the palette entry to get.

Return value

TRgb The rgb value of the palette entry

void SetEntry(TInt aPaletteIndex,const TRgb& aPaletteEntry);

Description

Sets the palette entry aPaletteIndex to the rgb value aPaletteEntry.

Parameters

TInt aPaletteIndex The index of the palette entry to be set. const TRgb& aPaletteEntry The rgb value to set that entry to.

TRgb NearestEntry(const TRgb& aColor) const;

Description

Gets the colour in the palette which is closest to the specified colour.

Parameters

const TRgb& aColor The colour to find.

Return value

TRgb The colour in the palette which is closest to the specified colour.

TInt NearestIndex(const TRgb& aColor) const;

Description

Gets the index of the colour in the palette which is closest to the specified colour.

Parameters

const TRgb& aColor The colour to find.

Return value

TInt The index of the colour in the palette which is closest to the specified colour.