LayoutEngine Class Reference

This is a virtual base class used to do complex text layout. More...

#include <LayoutEngine.h>

Inheritance diagram for LayoutEngine:
UObject UMemory

Public Member Functions

virtual ~LayoutEngine ()
 The destructor.
virtual le_int32 layoutChars (const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, float x, float y, LEErrorCode &success)
 This method will invoke the layout steps in their correct order by calling the computeGlyphs, positionGlyphs and adjustGlyphPosition methods.
le_int32 getGlyphCount () const
 This method returns the number of glyphs in the glyph array.
void getGlyphs (LEGlyphID glyphs[], LEErrorCode &success) const
 This method copies the glyph array into a caller supplied array.
virtual void getGlyphs (le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const
 This method copies the glyph array into a caller supplied array, ORing in extra bits.
void getCharIndices (le_int32 charIndices[], LEErrorCode &success) const
 This method copies the character index array into a caller supplied array.
void getCharIndices (le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const
 This method copies the character index array into a caller supplied array.
void getGlyphPositions (float positions[], LEErrorCode &success) const
 This method copies the position array into a caller supplied array.
void getGlyphPosition (le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const
 This method returns the X and Y position of the glyph at the given index.
virtual void reset ()
 This method frees the glyph, character index and position arrays so that the LayoutEngine can be reused to layout a different characer array.
virtual UClassID getDynamicClassID () const
 ICU "poor man's RTTI", returns a UClassID for the actual class.

Static Public Member Functions

static LayoutEnginelayoutEngineFactory (const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success)
 This method returns a LayoutEngine capable of laying out text in the given font, script and langauge.
static LayoutEnginelayoutEngineFactory (const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success)
 Override of existing call that provides flags to control typography.
static UClassID getStaticClassID ()
 ICU "poor man's RTTI", returns a UClassID for this class.

Protected Member Functions

 LayoutEngine (const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typoFlags, LEErrorCode &success)
 This constructs an instance for a given font, script and language.
 LayoutEngine ()
 This overrides the default no argument constructor to make it difficult for clients to call it.
virtual le_int32 characterProcessing (const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success)
 This method does any required pre-processing to the input characters.
virtual le_int32 computeGlyphs (const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success)
 This method does the glyph processing.
virtual void positionGlyphs (LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success)
 This method does basic glyph positioning.
virtual void adjustGlyphPositions (const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success)
 This method does positioning adjustments like accent positioning and kerning.
virtual const void * getFontTable (LETag tableTag) const
 This method gets a table from the font associated with the text.
virtual void mapCharsToGlyphs (const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success)
 This method does character to glyph mapping.

Static Protected Member Functions

static void adjustMarkGlyphs (LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success)
 This is a convenience method that forces the advance width of mark glyphs to be zero, which is required for proper selection and highlighting.
static void adjustMarkGlyphs (const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success)
 This is a convenience method that forces the advance width of mark glyphs to be zero, which is required for proper selection and highlighting.

Protected Attributes

LEGlyphStoragefGlyphStorage
 The object which holds the glyph storage.
const LEFontInstancefFontInstance
 The font instance for the text font.
le_int32 fScriptCode
 The script code for the text.
le_int32 fLanguageCode
 The langauge code for the text.
le_int32 fTypoFlags
 The typographic control flags.
le_bool fFilterZeroWidth
 TRUE if mapCharsToGlyphs should replace ZWJ / ZWNJ with a glyph with no contours.

Detailed Description

This is a virtual base class used to do complex text layout.

The text must all be in a single font, script, and language. An instance of a LayoutEngine can be created by calling the layoutEngineFactory method. Fonts are identified by instances of the LEFontInstance class. Script and language codes are identified by integer codes, which are defined in ScriptAndLanuageTags.h.

Note that this class is not public API. It is declared public so that it can be exported from the library that it is a part of.

The input to the layout process is an array of characters in logical order, and a starting X, Y position for the text. The output is an array of glyph indices, an array of character indices for the glyphs, and an array of glyph positions. These arrays are protected members of LayoutEngine which can be retreived by a public method. The reset method can be called to free these arrays so that the LayoutEngine can be reused.

The layout process is done in three steps. There is a protected virtual method for each step. These methods have a default implementation which only does character to glyph mapping and default positioning using the glyph's advance widths. Subclasses can override these methods for more advanced layout. There is a public method which invokes the steps in the correct order.

The steps are:

1) Glyph processing - character to glyph mapping and any other glyph processing such as ligature substitution and contextual forms.

2) Glyph positioning - position the glyphs based on their advance widths.

3) Glyph position adjustments - adjustment of glyph positions for kerning, accent placement, etc.

NOTE: in all methods below, output parameters are references to pointers so the method can allocate and free the storage as needed. All storage allocated in this way is owned by the object which created it, and will be freed when it is no longer needed, or when the object's destructor is invoked.

See also:
LEFontInstance
ScriptAndLanguageTags.h
Stable:
ICU 2.8

Definition at line 67 of file LayoutEngine.h.


Constructor & Destructor Documentation

LayoutEngine::LayoutEngine ( const LEFontInstance fontInstance,
le_int32  scriptCode,
le_int32  languageCode,
le_int32  typoFlags,
LEErrorCode success 
) [protected]

This constructs an instance for a given font, script and language.

Subclass constructors must call this constructor.

Parameters:
fontInstance - the font for the text
scriptCode - the script for the text
languageCode - the language for the text
typoFlags - the typographic control flags for the text. Set bit 1 if kerning is desired, set bit 2 if ligature formation is desired. Others are reserved.
success - set to an error code if the operation fails
See also:
LEFontInstance
ScriptAndLanguageTags.h
Internal:
Do not use. This API is for internal use only.
LayoutEngine::LayoutEngine (  )  [protected]

This overrides the default no argument constructor to make it difficult for clients to call it.

Clients are expected to call layoutEngineFactory.

Internal:
Do not use. This API is for internal use only.
virtual LayoutEngine::~LayoutEngine (  )  [virtual]

The destructor.

It will free any storage allocated for the glyph, character index and position arrays by calling the reset method. It is declared virtual so that it will be invoked by the subclass destructors.

Stable:
ICU 2.8

Member Function Documentation

virtual void LayoutEngine::adjustGlyphPositions ( const LEUnicode  chars[],
le_int32  offset,
le_int32  count,
le_bool  reverse,
LEGlyphStorage glyphStorage,
LEErrorCode success 
) [protected, virtual]

This method does positioning adjustments like accent positioning and kerning.

The default implementation does nothing. Subclasses needing position adjustments must override this method.

Note that this method has both characters and glyphs as input so that it can use the character codes to determine glyph types if that information isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF table)

Parameters:
chars - the input character context
offset - the offset of the first character to process
count - the number of characters to process
reverse - TRUE if the glyphs in the glyph array have been reordered
glyphStorage - the object which holds the per-glyph storage. The glyph positions will be adjusted as needed.
success - output parameter set to an error code if the operation fails
Internal:
Do not use. This API is for internal use only.
static void LayoutEngine::adjustMarkGlyphs ( const LEUnicode  chars[],
le_int32  charCount,
le_bool  reverse,
LEGlyphStorage glyphStorage,
LEGlyphFilter *  markFilter,
LEErrorCode success 
) [static, protected]

This is a convenience method that forces the advance width of mark glyphs to be zero, which is required for proper selection and highlighting.

This method uses the input characters to identify marks. This is required in cases where the font does not contain enough information to identify them based on the glyph IDs.

Parameters:
chars - the array of input characters
charCount - the number of input characers
glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
reverse - TRUE if the glyph array has been reordered
markFilter - used to identify mark glyphs
success - output parameter set to an error code if the operation fails
See also:
LEGlyphFilter
Internal:
Do not use. This API is for internal use only.
static void LayoutEngine::adjustMarkGlyphs ( LEGlyphStorage glyphStorage,
LEGlyphFilter *  markFilter,
LEErrorCode success 
) [static, protected]

This is a convenience method that forces the advance width of mark glyphs to be zero, which is required for proper selection and highlighting.

Parameters:
glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
markFilter - used to identify mark glyphs
success - output parameter set to an error code if the operation fails
See also:
LEGlyphFilter
Internal:
Do not use. This API is for internal use only.
virtual le_int32 LayoutEngine::characterProcessing ( const LEUnicode  chars[],
le_int32  offset,
le_int32  count,
le_int32  max,
le_bool  rightToLeft,
LEUnicode *&  outChars,
LEGlyphStorage glyphStorage,
LEErrorCode success 
) [protected, virtual]

This method does any required pre-processing to the input characters.

It may generate output characters that differ from the input charcters due to insertions, deletions, or reorderings. In such cases, it will also generate an output character index array reflecting these changes.

Subclasses must override this method.

Input parameters:

Parameters:
chars - the input character context
offset - the index of the first character to process
count - the number of characters to process
max - the number of characters in the input context
rightToLeft - TRUE if the characters are in a right to left directional run
outChars - the output character array, if different from the input
glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
success - set to an error code if the operation fails
Returns:
the output character count (input character count if no change)
Internal:
Do not use. This API is for internal use only.
virtual le_int32 LayoutEngine::computeGlyphs ( const LEUnicode  chars[],
le_int32  offset,
le_int32  count,
le_int32  max,
le_bool  rightToLeft,
LEGlyphStorage glyphStorage,
LEErrorCode success 
) [protected, virtual]

This method does the glyph processing.

It converts an array of characters into an array of glyph indices and character indices. The characters to be processed are passed in a surrounding context. The context is specified as a starting address and a maximum character count. An offset and a count are used to specify the characters to be processed.

The default implementation of this method only does character to glyph mapping. Subclasses needing more elaborate glyph processing must override this method.

Input parameters:

Parameters:
chars - the character context
offset - the offset of the first character to process
count - the number of characters to process
max - the number of characters in the context.
rightToLeft - TRUE if the text is in a right to left directional run
glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays will be set.

Output parameters:

Parameters:
success - set to an error code if the operation fails
Returns:
the number of glyphs in the glyph index array
Internal:
Do not use. This API is for internal use only.
void LayoutEngine::getCharIndices ( le_int32  charIndices[],
le_int32  indexBase,
LEErrorCode success 
) const

This method copies the character index array into a caller supplied array.

The caller must ensure that the array is large enough to hold a character index for each glyph.

Parameters:
charIndices - the destiniation character index array
indexBase - an offset which will be added to each index
success - set to an error code if the operation fails
Stable:
ICU 2.8
void LayoutEngine::getCharIndices ( le_int32  charIndices[],
LEErrorCode success 
) const

This method copies the character index array into a caller supplied array.

The caller must ensure that the array is large enough to hold a character index for each glyph.

Parameters:
charIndices - the destiniation character index array
success - set to an error code if the operation fails
Stable:
ICU 2.8
virtual UClassID LayoutEngine::getDynamicClassID (  )  const [virtual]

ICU "poor man's RTTI", returns a UClassID for the actual class.

Stable:
ICU 2.8

Implements UObject.

virtual const void* LayoutEngine::getFontTable ( LETag  tableTag  )  const [protected, virtual]

This method gets a table from the font associated with the text.

The default implementation gets the table from the font instance. Subclasses which need to get the tables some other way must override this method.

Parameters:
tableTag - the four byte table tag.
Returns:
the address of the table.
Internal:
Do not use. This API is for internal use only.
le_int32 LayoutEngine::getGlyphCount (  )  const

This method returns the number of glyphs in the glyph array.

Note that the number of glyphs will be greater than or equal to the number of characters used to create the LayoutEngine.

Returns:
the number of glyphs in the glyph array
Stable:
ICU 2.8
void LayoutEngine::getGlyphPosition ( le_int32  glyphIndex,
float &  x,
float &  y,
LEErrorCode success 
) const

This method returns the X and Y position of the glyph at the given index.

Input parameters:

Parameters:
glyphIndex - the index of the glyph

Output parameters:

Parameters:
x - the glyph's X position
y - the glyph's Y position
success - set to an error code if the operation fails
Stable:
ICU 2.8
void LayoutEngine::getGlyphPositions ( float  positions[],
LEErrorCode success 
) const

This method copies the position array into a caller supplied array.

The caller must ensure that the array is large enough to hold an X and Y position for each glyph, plus an extra X and Y for the advance of the last glyph.

Parameters:
positions - the destiniation position array
success - set to an error code if the operation fails
Stable:
ICU 2.8
virtual void LayoutEngine::getGlyphs ( le_uint32  glyphs[],
le_uint32  extraBits,
LEErrorCode success 
) const [virtual]

This method copies the glyph array into a caller supplied array, ORing in extra bits.

(This functionality is needed by the JDK, which uses 32 bits pre glyph idex, with the high 16 bits encoding the composite font slot number)

Parameters:
glyphs - the destination (32 bit) glyph array
extraBits - this value will be ORed with each glyph index
success - set to an error code if the operation fails
Stable:
ICU 2.8
void LayoutEngine::getGlyphs ( LEGlyphID  glyphs[],
LEErrorCode success 
) const

This method copies the glyph array into a caller supplied array.

The caller must ensure that the array is large enough to hold all the glyphs.

Parameters:
glyphs - the destiniation glyph array
success - set to an error code if the operation fails
Stable:
ICU 2.8
static UClassID LayoutEngine::getStaticClassID (  )  [static]

ICU "poor man's RTTI", returns a UClassID for this class.

Stable:
ICU 2.8
virtual le_int32 LayoutEngine::layoutChars ( const LEUnicode  chars[],
le_int32  offset,
le_int32  count,
le_int32  max,
le_bool  rightToLeft,
float  x,
float  y,
LEErrorCode success 
) [virtual]

This method will invoke the layout steps in their correct order by calling the computeGlyphs, positionGlyphs and adjustGlyphPosition methods.

It will compute the glyph, character index and position arrays.

Parameters:
chars - the input character context
offset - the offset of the first character to process
count - the number of characters to process
max - the number of characters in the input context
rightToLeft - TRUE if the characers are in a right to left directional run
x - the initial X position
y - the initial Y position
success - output parameter set to an error code if the operation fails
Returns:
the number of glyphs in the glyph array

Note: The glyph, character index and position array can be accessed using the getter methods below.

Note: If you call this method more than once, you must call the reset() method first to free the glyph, character index and position arrays allocated by the previous call.

Stable:
ICU 2.8
static LayoutEngine* LayoutEngine::layoutEngineFactory ( const LEFontInstance fontInstance,
le_int32  scriptCode,
le_int32  languageCode,
le_int32  typo_flags,
LEErrorCode success 
) [static]

Override of existing call that provides flags to control typography.

Stable:
ICU 3.4
static LayoutEngine* LayoutEngine::layoutEngineFactory ( const LEFontInstance fontInstance,
le_int32  scriptCode,
le_int32  languageCode,
LEErrorCode success 
) [static]

This method returns a LayoutEngine capable of laying out text in the given font, script and langauge.

Note that the LayoutEngine returned may be a subclass of LayoutEngine.

Parameters:
fontInstance - the font of the text
scriptCode - the script of the text
languageCode - the language of the text
success - output parameter set to an error code if the operation fails
Returns:
a LayoutEngine which can layout text in the given font.
See also:
LEFontInstance
Stable:
ICU 2.8
virtual void LayoutEngine::mapCharsToGlyphs ( const LEUnicode  chars[],
le_int32  offset,
le_int32  count,
le_bool  reverse,
le_bool  mirror,
LEGlyphStorage glyphStorage,
LEErrorCode success 
) [protected, virtual]

This method does character to glyph mapping.

The default implementation uses the font instance to do the mapping. It will allocate the glyph and character index arrays if they're not already allocated. If it allocates the character index array, it will fill it it.

This method supports right to left text with the ability to store the glyphs in reverse order, and by supporting character mirroring, which will replace a character which has a left and right form, such as parens, with the opposite form before mapping it to a glyph index.

Input parameters:

Parameters:
chars - the input character context
offset - the offset of the first character to be mapped
count - the number of characters to be mapped
reverse - if TRUE, the output will be in reverse order
mirror - if TRUE, do character mirroring
glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays will be filled in.
success - set to an error code if the operation fails
See also:
LEFontInstance
Internal:
Do not use. This API is for internal use only.
virtual void LayoutEngine::positionGlyphs ( LEGlyphStorage glyphStorage,
float  x,
float  y,
LEErrorCode success 
) [protected, virtual]

This method does basic glyph positioning.

The default implementation positions the glyphs based on their advance widths. This is sufficient for most uses. It is not expected that many subclasses will override this method.

Input parameters:

Parameters:
glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
x - the starting X position
y - the starting Y position
success - set to an error code if the operation fails
Internal:
Do not use. This API is for internal use only.
virtual void LayoutEngine::reset (  )  [virtual]

This method frees the glyph, character index and position arrays so that the LayoutEngine can be reused to layout a different characer array.

(This method is also called by the destructor)

Stable:
ICU 2.8

Field Documentation

TRUE if mapCharsToGlyphs should replace ZWJ / ZWNJ with a glyph with no contours.

Internal:
Do not use. This API is for internal use only.

Definition at line 116 of file LayoutEngine.h.

The font instance for the text font.

See also:
LEFontInstance
Internal:
Do not use. This API is for internal use only.

Definition at line 83 of file LayoutEngine.h.

The object which holds the glyph storage.

Internal:
Do not use. This API is for internal use only.

Definition at line 74 of file LayoutEngine.h.

The langauge code for the text.

See also:
ScriptAndLanguageTags.h for language codes.
Internal:
Do not use. This API is for internal use only.

Definition at line 101 of file LayoutEngine.h.

The script code for the text.

See also:
ScriptAndLanguageTags.h for script codes.
Internal:
Do not use. This API is for internal use only.

Definition at line 92 of file LayoutEngine.h.

The typographic control flags.

Internal:
Do not use. This API is for internal use only.

Definition at line 108 of file LayoutEngine.h.


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Generated on Sat Jan 23 15:17:43 2010 for ICU 4.3.4 by  doxygen 1.6.1