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* (C) Copyright IBM Corp. 1998-2008 - All Rights Reserved
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#ifndef __LAYOUTENGINE_H
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#define __LAYOUTENGINE_H
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* \brief C++ API: Virtual base class for complex text layout.
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* This is a virtual base class used to do complex text layout. The text must all
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* be in a single font, script, and language. An instance of a LayoutEngine can be
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* created by calling the layoutEngineFactory method. Fonts are identified by
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* instances of the LEFontInstance class. Script and language codes are identified
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* by integer codes, which are defined in ScriptAndLanuageTags.h.
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* Note that this class is not public API. It is declared public so that it can be
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* exported from the library that it is a part of.
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* The input to the layout process is an array of characters in logical order,
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* and a starting X, Y position for the text. The output is an array of glyph indices,
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* an array of character indices for the glyphs, and an array of glyph positions.
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* These arrays are protected members of LayoutEngine which can be retreived by a
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* public method. The reset method can be called to free these arrays so that the
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* LayoutEngine can be reused.
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* The layout process is done in three steps. There is a protected virtual method
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* for each step. These methods have a default implementation which only does
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* character to glyph mapping and default positioning using the glyph's advance
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* widths. Subclasses can override these methods for more advanced layout.
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* There is a public method which invokes the steps in the correct order.
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* 1) Glyph processing - character to glyph mapping and any other glyph processing
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* such as ligature substitution and contextual forms.
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* 2) Glyph positioning - position the glyphs based on their advance widths.
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* 3) Glyph position adjustments - adjustment of glyph positions for kerning,
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* accent placement, etc.
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* NOTE: in all methods below, output parameters are references to pointers so
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* the method can allocate and free the storage as needed. All storage allocated
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* in this way is owned by the object which created it, and will be freed when it
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* is no longer needed, or when the object's destructor is invoked.
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* @see ScriptAndLanguageTags.h
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class U_LAYOUT_API LayoutEngine : public UObject {
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* The object which holds the glyph storage
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LEGlyphStorage *fGlyphStorage;
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* The font instance for the text font.
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const LEFontInstance *fFontInstance;
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* The script code for the text
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* @see ScriptAndLanguageTags.h for script codes.
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* The langauge code for the text
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* @see ScriptAndLanguageTags.h for language codes.
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le_int32 fLanguageCode;
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* The typographic control flags
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* <code>TRUE</code> if <code>mapCharsToGlyphs</code> should replace ZWJ / ZWNJ with a glyph
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le_bool fFilterZeroWidth;
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* This constructs an instance for a given font, script and language. Subclass constructors
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* must call this constructor.
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* @param fontInstance - the font for the text
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* @param scriptCode - the script for the text
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* @param languageCode - the language for the text
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* @param typoFlags - the typographic control flags for the text. Set bit 1 if kerning
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* is desired, set bit 2 if ligature formation is desired. Others are reserved.
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* @param success - set to an error code if the operation fails
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* @see LEFontInstance
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* @see ScriptAndLanguageTags.h
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LayoutEngine(const LEFontInstance *fontInstance,
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le_int32 languageCode,
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LEErrorCode &success);
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* This overrides the default no argument constructor to make it
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* difficult for clients to call it. Clients are expected to call
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* layoutEngineFactory.
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* This method does any required pre-processing to the input characters. It
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* may generate output characters that differ from the input charcters due to
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* insertions, deletions, or reorderings. In such cases, it will also generate an
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* output character index array reflecting these changes.
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* Subclasses must override this method.
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* @param chars - the input character context
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* @param offset - the index of the first character to process
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* @param count - the number of characters to process
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* @param max - the number of characters in the input context
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* @param rightToLeft - TRUE if the characters are in a right to left directional run
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* @param outChars - the output character array, if different from the input
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* @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
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* @param success - set to an error code if the operation fails
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* @return the output character count (input character count if no change)
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virtual le_int32 characterProcessing(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft,
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LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success);
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* This method does the glyph processing. It converts an array of characters
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* into an array of glyph indices and character indices. The characters to be
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* processed are passed in a surrounding context. The context is specified as
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* a starting address and a maximum character count. An offset and a count are
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* used to specify the characters to be processed.
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* The default implementation of this method only does character to glyph mapping.
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* Subclasses needing more elaborate glyph processing must override this method.
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* @param chars - the character context
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* @param offset - the offset of the first character to process
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* @param count - the number of characters to process
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* @param max - the number of characters in the context.
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* @param rightToLeft - TRUE if the text is in a right to left directional run
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* @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
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* @param success - set to an error code if the operation fails
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* @return the number of glyphs in the glyph index array
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virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success);
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* This method does basic glyph positioning. The default implementation positions
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* the glyphs based on their advance widths. This is sufficient for most uses. It
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* is not expected that many subclasses will override this method.
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* @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
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* @param x - the starting X position
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* @param y - the starting Y position
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* @param success - set to an error code if the operation fails
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virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
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* This method does positioning adjustments like accent positioning and
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* kerning. The default implementation does nothing. Subclasses needing
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* position adjustments must override this method.
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* Note that this method has both characters and glyphs as input so that
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* it can use the character codes to determine glyph types if that information
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* isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
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* @param chars - the input character context
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* @param offset - the offset of the first character to process
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* @param count - the number of characters to process
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* @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
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* @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
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* adjusted as needed.
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* @param success - output parameter set to an error code if the operation fails
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virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
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* This method gets a table from the font associated with
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* the text. The default implementation gets the table from
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* the font instance. Subclasses which need to get the tables
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* some other way must override this method.
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* @param tableTag - the four byte table tag.
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* @return the address of the table.
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virtual const void *getFontTable(LETag tableTag) const;
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* This method does character to glyph mapping. The default implementation
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* uses the font instance to do the mapping. It will allocate the glyph and
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* character index arrays if they're not already allocated. If it allocates the
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* character index array, it will fill it it.
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* This method supports right to left
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* text with the ability to store the glyphs in reverse order, and by supporting
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* character mirroring, which will replace a character which has a left and right
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* form, such as parens, with the opposite form before mapping it to a glyph index.
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* @param chars - the input character context
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* @param offset - the offset of the first character to be mapped
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* @param count - the number of characters to be mapped
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* @param reverse - if <code>TRUE</code>, the output will be in reverse order
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* @param mirror - if <code>TRUE</code>, do character mirroring
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* @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
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* indices arrays will be filled in.
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* @param success - set to an error code if the operation fails
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* @see LEFontInstance
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virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
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* This is a convenience method that forces the advance width of mark
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* glyphs to be zero, which is required for proper selection and highlighting.
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* @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
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* @param markFilter - used to identify mark glyphs
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* @param success - output parameter set to an error code if the operation fails
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static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
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* This is a convenience method that forces the advance width of mark
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* glyphs to be zero, which is required for proper selection and highlighting.
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* This method uses the input characters to identify marks. This is required in
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* cases where the font does not contain enough information to identify them based
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* @param chars - the array of input characters
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* @param charCount - the number of input characers
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* @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
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* @param reverse - <code>TRUE</code> if the glyph array has been reordered
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* @param markFilter - used to identify mark glyphs
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* @param success - output parameter set to an error code if the operation fails
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static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
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* The destructor. It will free any storage allocated for the
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* glyph, character index and position arrays by calling the reset
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* method. It is declared virtual so that it will be invoked by the
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* subclass destructors.
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virtual ~LayoutEngine();
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* This method will invoke the layout steps in their correct order by calling
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* the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
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* compute the glyph, character index and position arrays.
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* @param chars - the input character context
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* @param offset - the offset of the first character to process
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* @param count - the number of characters to process
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* @param max - the number of characters in the input context
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* @param rightToLeft - TRUE if the characers are in a right to left directional run
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* @param x - the initial X position
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* @param y - the initial Y position
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* @param success - output parameter set to an error code if the operation fails
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* @return the number of glyphs in the glyph array
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* Note: The glyph, character index and position array can be accessed
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* using the getter methods below.
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* Note: If you call this method more than once, you must call the reset()
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* method first to free the glyph, character index and position arrays
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* allocated by the previous call.
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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);
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* This method returns the number of glyphs in the glyph array. Note
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* that the number of glyphs will be greater than or equal to the number
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* of characters used to create the LayoutEngine.
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* @return the number of glyphs in the glyph array
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le_int32 getGlyphCount() const;
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* This method copies the glyph array into a caller supplied array.
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* The caller must ensure that the array is large enough to hold all
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* @param glyphs - the destiniation glyph array
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* @param success - set to an error code if the operation fails
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void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
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* This method copies the glyph array into a caller supplied array,
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* ORing in extra bits. (This functionality is needed by the JDK,
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* which uses 32 bits pre glyph idex, with the high 16 bits encoding
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* the composite font slot number)
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* @param glyphs - the destination (32 bit) glyph array
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* @param extraBits - this value will be ORed with each glyph index
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* @param success - set to an error code if the operation fails
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virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
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* This method copies the character index array into a caller supplied array.
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* The caller must ensure that the array is large enough to hold a
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* character index for each glyph.
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* @param charIndices - the destiniation character index array
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* @param success - set to an error code if the operation fails
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void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
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* This method copies the character index array into a caller supplied array.
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* The caller must ensure that the array is large enough to hold a
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* character index for each glyph.
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* @param charIndices - the destiniation character index array
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* @param indexBase - an offset which will be added to each index
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* @param success - set to an error code if the operation fails
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void getCharIndices(le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const;
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* This method copies the position array into a caller supplied array.
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* The caller must ensure that the array is large enough to hold an
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* X and Y position for each glyph, plus an extra X and Y for the
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* advance of the last glyph.
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* @param positions - the destiniation position array
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* @param success - set to an error code if the operation fails
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void getGlyphPositions(float positions[], LEErrorCode &success) const;
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* This method returns the X and Y position of the glyph at
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* @param glyphIndex - the index of the glyph
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* @param x - the glyph's X position
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* @param y - the glyph's Y position
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* @param success - set to an error code if the operation fails
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void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
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* This method frees the glyph, character index and position arrays
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* so that the LayoutEngine can be reused to layout a different
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* characer array. (This method is also called by the destructor)
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virtual void reset();
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* This method returns a LayoutEngine capable of laying out text
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* in the given font, script and langauge. Note that the LayoutEngine
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* returned may be a subclass of LayoutEngine.
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* @param fontInstance - the font of the text
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* @param scriptCode - the script of the text
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* @param languageCode - the language of the text
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* @param success - output parameter set to an error code if the operation fails
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* @return a LayoutEngine which can layout text in the given font.
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* @see LEFontInstance
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static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
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* Override of existing call that provides flags to control typography.
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static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
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* ICU "poor man's RTTI", returns a UClassID for the actual class.
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virtual UClassID getDynamicClassID() const;
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* ICU "poor man's RTTI", returns a UClassID for this class.
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static UClassID getStaticClassID();
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source/layout/LayoutEngine.h
