Qt 4.8: QAbstractFontEngine Class Reference

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# QAbstractFontEngine Class Reference

The QAbstractFontEngine class is the base class for font engine plugins in Qt for Embedded Linux. More...

     #include <QAbstractFontEngine>

This class is under development and is subject to change.

Inherits: QObject.

This class was introduced in Qt 4.3.

- List of all members, including inherited members

## Public Types

class | FixedPoint`(preliminary)`
class | GlyphMetrics`(preliminary)`
flags | Capabilities
enum | Capability { CanRenderGlyphs_Gray, CanRenderGlyphs_Mono, CanRenderGlyphs, CanOutlineGlyphs }
typedef | Fixed
enum | FontProperty { Ascent, Descent, Leading, XHeight, ..., OutlineGlyphsHint }
enum | TextShapingFlag { RightToLeft, ReturnDesignMetrics }
flags | TextShapingFlags

## Public Functions

| QAbstractFontEngine ( QObject * parent = 0 )
| ~QAbstractFontEngine ()
virtual void | addGlyphOutlinesToPath ( uint * glyphs, int numGlyphs, FixedPoint * positions, QPainterPath * path )
virtual Capabilities | capabilities () const = 0
virtual bool | convertStringToGlyphIndices ( const QChar * string, int length, uint * glyphs, int * numGlyphs, TextShapingFlags flags ) const = 0
virtual QVariant | fontProperty ( FontProperty property ) const = 0
virtual void | getGlyphAdvances ( const uint * glyphs, int numGlyphs, Fixed * advances, TextShapingFlags flags ) const = 0
virtual GlyphMetrics | glyphMetrics ( uint glyph ) const = 0
virtual bool | renderGlyph ( uint glyph, int depth, int bytesPerLine, int height, uchar * buffer )

- 29 public functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 1 signal inherited from QObject
- 7 static public members inherited from QObject
- 8 protected functions inherited from QObject

## Detailed Description

The QAbstractFontEngine class is the base class for font engine plugins in Qt for Embedded Linux.

QAbstractFontEngine is implemented by font engine plugins through QFontEnginePlugin.

See also QFontEnginePlugin and QFontEngineInfo.

## Member Type Documentation

### enum QAbstractFontEngine::Capability
flags QAbstractFontEngine::Capabilities

This enum describes the capabilities of a font engine.

Constant | Value | Description
--- | --- | ---
`QAbstractFontEngine::CanRenderGlyphs_Gray` | `4` | The font engine can render individual glyphs into 8 bpp images.
`QAbstractFontEngine::CanRenderGlyphs_Mono` | `2` | The font engine can render individual glyphs into 1 bpp images.
`QAbstractFontEngine::CanRenderGlyphs` | `CanRenderGlyphs_Mono | CanRenderGlyphs_Gray` | The font engine can render individual glyphs into images.
`QAbstractFontEngine::CanOutlineGlyphs` | `1` | The font engine can convert glyphs to painter paths.

The Capabilities type is a typedef for QFlags<Capability>. It stores an OR combination of Capability values.

### typedef QAbstractFontEngine::Fixed

This type is `int`, interpreted as a 26.6 fixed point value.

### enum QAbstractFontEngine::FontProperty

This enum describes the properties of a font provided by a font engine.

Constant | Value | Description
--- | --- | ---
`QAbstractFontEngine::Ascent` | `0` | The ascent of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::Descent` | `1` | The descent of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::Leading` | `2` | The leading of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::XHeight` | `3` | The 'x' height of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::AverageCharWidth` | `4` | The average character width of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::LineThickness` | `5` | The thickness of the underline and strikeout lines for the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::UnderlinePosition` | `6` | The distance from the base line to the underline position for the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::MaxCharWidth` | `7` | The width of the widest character in the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::MinLeftBearing` | `8` | The minimum left bearing of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::MinRightBearing` | `9` | The maximum right bearing of the font, specified as a 26.6 fixed point value.
`QAbstractFontEngine::GlyphCount` | `10` | The number of glyphs in the font, specified as an integer value.
`QAbstractFontEngine::CacheGlyphsHint` | `11` | A boolean value specifying whether rendered glyphs should be cached by Qt.
`QAbstractFontEngine::OutlineGlyphsHint` | `12` | A boolean value specifying whether the font engine prefers outline drawing over image rendering for uncached glyphs.

### enum QAbstractFontEngine::TextShapingFlag
flags QAbstractFontEngine::TextShapingFlags

This enum describes flags controlling conversion of characters to glyphs and their metrics.

Constant | Value | Description
--- | --- | ---
`QAbstractFontEngine::RightToLeft` | `0x0001` | The text is used in a right-to-left context.
`QAbstractFontEngine::ReturnDesignMetrics` | `0x0002` | Return font design metrics instead of pixel metrics.

The TextShapingFlags type is a typedef for QFlags<TextShapingFlag>. It stores an OR combination of TextShapingFlag values.

## Member Function Documentation

### QAbstractFontEngine::QAbstractFontEngine ( QObject * parent = 0 )

Constructs a new QAbstractFontEngine with the given parent.

### QAbstractFontEngine::~QAbstractFontEngine ()

Destroys this QAbstractFontEngine object.

### void QAbstractFontEngine::addGlyphOutlinesToPath ( uint * glyphs, int numGlyphs, FixedPoint * positions, QPainterPath * path )`[virtual]`

Implemented in subclasses to add the outline of the glyphs specified by glyphs and numGlyphs at the specified positions to the painter path path.

### Capabilities QAbstractFontEngine::capabilities () const`[pure virtual]`

Implemented in subclasses to specify the font engine's capabilities. The return value may be cached by the caller and is expected not to change during the lifetime of the font engine.

### bool QAbstractFontEngine::convertStringToGlyphIndices ( const QChar * string, int length, uint * glyphs, int * numGlyphs, TextShapingFlags flags ) const`[pure virtual]`

Implemented in subclasses to convert the characters specified by string and length to glyph indicies, using flags. The glyph indicies should be returned in the glyphs array provided by the caller. The maximum size of glyphs is specified by the value pointed to by numGlyphs. If successful, the subclass implementation sets the value pointed to by numGlyphs to the actual number of glyph indices generated, and returns true. Otherwise, e.g. if there is not enough space in the provided glyphs array, it should set numGlyphs to the number of glyphs needed for the conversion and return false.

### QVariant QAbstractFontEngine::fontProperty ( FontProperty property ) const`[pure virtual]`

Implemented in subclasses to return the value of the font attribute property. The return value may be cached by the caller and is expected not to change during the lifetime of the font engine.

### void QAbstractFontEngine::getGlyphAdvances ( const uint * glyphs, int numGlyphs, Fixed * advances, TextShapingFlags flags ) const`[pure virtual]`

Implemented in subclasses to retrieve the advances of the array specified by glyphs and numGlyphs, using flags. The result is returned in advances, which is allocated by the caller and contains numGlyphs elements.

### GlyphMetrics QAbstractFontEngine::glyphMetrics ( uint glyph ) const`[pure virtual]`

Implemented in subclass to return the metrics for glyph.

### bool QAbstractFontEngine::renderGlyph ( uint glyph, int depth, int bytesPerLine, int height, uchar * buffer )`[virtual]`

Implemented in subclasses to render the specified glyph into a buffer with the given depth , bytesPerLine and height.

Returns true if rendering succeeded, false otherwise.