/*
*
* (C) Copyright IBM Corp. 1998-2008 - All Rights Reserved
*
*/
#ifndef __LAYOUTENGINE_H
#define __LAYOUTENGINE_H
#include "LETypes.h"
/**
* \file
* \brief C++ API: Virtual base class for complex text layout.
*/
U_NAMESPACE_BEGIN
class LEFontInstance;
class LEGlyphFilter;
class LEGlyphStorage;
/**
* 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 LEFontInstance
* @see ScriptAndLanguageTags.h
*
* @stable ICU 2.8
*/
class U_LAYOUT_API LayoutEngine : public UObject {
protected:
/**
* The object which holds the glyph storage
*
* @internal
*/
LEGlyphStorage *fGlyphStorage;
/**
* The font instance for the text font.
*
* @see LEFontInstance
*
* @internal
*/
const LEFontInstance *fFontInstance;
/**
* The script code for the text
*
* @see ScriptAndLanguageTags.h for script codes.
*
* @internal
*/
le_int32 fScriptCode;
/**
* The langauge code for the text
*
* @see ScriptAndLanguageTags.h for language codes.
*
* @internal
*/
le_int32 fLanguageCode;
/**
* The typographic control flags
*
* @internal
*/
le_int32 fTypoFlags;
/**
* <code>TRUE</code> if <code>mapCharsToGlyphs</code> should replace ZWJ / ZWNJ with a glyph
* with no contours.
*
* @internal
*/
le_bool fFilterZeroWidth;
/**
* This constructs an instance for a given font, script and language. Subclass constructors
* must call this constructor.
*
* @param fontInstance - the font for the text
* @param scriptCode - the script for the text
* @param languageCode - the language for the text
* @param 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.
* @param success - set to an error code if the operation fails
*
* @see LEFontInstance
* @see ScriptAndLanguageTags.h
*
* @internal
*/
LayoutEngine(const LEFontInstance *fontInstance,
le_int32 scriptCode,
le_int32 languageCode,
le_int32 typoFlags,
LEErrorCode &success);
/**
* This overrides the default no argument constructor to make it
* difficult for clients to call it. Clients are expected to call
* layoutEngineFactory.
*
* @internal
*/
LayoutEngine();
/**
* 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:
* @param chars - the input character context
* @param offset - the index of the first character to process
* @param count - the number of characters to process
* @param max - the number of characters in the input context
* @param rightToLeft - TRUE if the characters are in a right to left directional run
* @param outChars - the output character array, if different from the input
* @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
* @param success - set to an error code if the operation fails
*
* @return the output character count (input character count if no change)
*
* @internal
*/
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 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:
* @param chars - the character context
* @param offset - the offset of the first character to process
* @param count - the number of characters to process
* @param max - the number of characters in the context.
* @param rightToLeft - TRUE if the text is in a right to left directional run
* @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
* will be set.
*
* Output parameters:
* @param success - set to an error code if the operation fails
*
* @return the number of glyphs in the glyph index array
*
* @internal
*/
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 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:
* @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
* @param x - the starting X position
* @param y - the starting Y position
* @param success - set to an error code if the operation fails
*
* @internal
*/
virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
/**
* 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)
*
* @param chars - the input character context
* @param offset - the offset of the first character to process
* @param count - the number of characters to process
* @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
* @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
* adjusted as needed.
* @param success - output parameter set to an error code if the operation fails
*
* @internal
*/
virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
/**
* 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.
*
* @param tableTag - the four byte table tag.
*
* @return the address of the table.
*
* @internal
*/
virtual const void *getFontTable(LETag tableTag) const;
/**
* 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:
* @param chars - the input character context
* @param offset - the offset of the first character to be mapped
* @param count - the number of characters to be mapped
* @param reverse - if <code>TRUE</code>, the output will be in reverse order
* @param mirror - if <code>TRUE</code>, do character mirroring
* @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
* indices arrays will be filled in.
* @param success - set to an error code if the operation fails
*
* @see LEFontInstance
*
* @internal
*/
virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, 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.
*
* @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
* @param markFilter - used to identify mark glyphs
* @param success - output parameter set to an error code if the operation fails
*
* @see LEGlyphFilter
*
* @internal
*/
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.
* 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.
*
* @param chars - the array of input characters
* @param charCount - the number of input characers
* @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
* @param reverse - <code>TRUE</code> if the glyph array has been reordered
* @param markFilter - used to identify mark glyphs
* @param success - output parameter set to an error code if the operation fails
*
* @see LEGlyphFilter
*
* @internal
*/
static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
public:
/**
* 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
*/
virtual ~LayoutEngine();
/**
* 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.
*
* @param chars - the input character context
* @param offset - the offset of the first character to process
* @param count - the number of characters to process
* @param max - the number of characters in the input context
* @param rightToLeft - TRUE if the characers are in a right to left directional run
* @param x - the initial X position
* @param y - the initial Y position
* @param success - output parameter set to an error code if the operation fails
*
* @return 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
*/
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 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.
*
* @return the number of glyphs in the glyph array
*
* @stable ICU 2.8
*/
le_int32 getGlyphCount() 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.
*
* @param glyphs - the destiniation glyph array
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
/**
* 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)
*
* @param glyphs - the destination (32 bit) glyph array
* @param extraBits - this value will be ORed with each glyph index
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, 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.
*
* @param charIndices - the destiniation character index array
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
void 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.
*
* @param charIndices - the destiniation character index array
* @param indexBase - an offset which will be added to each index
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
void getCharIndices(le_int32 charIndices[], le_int32 indexBase, 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.
*
* @param positions - the destiniation position array
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
void getGlyphPositions(float positions[], LEErrorCode &success) const;
/**
* This method returns the X and Y position of the glyph at
* the given index.
*
* Input parameters:
* @param glyphIndex - the index of the glyph
*
* Output parameters:
* @param x - the glyph's X position
* @param y - the glyph's Y position
* @param success - set to an error code if the operation fails
*
* @stable ICU 2.8
*/
void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
/**
* 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
*/
virtual void reset();
/**
* 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.
*
* @param fontInstance - the font of the text
* @param scriptCode - the script of the text
* @param languageCode - the language of the text
* @param success - output parameter set to an error code if the operation fails
*
* @return a LayoutEngine which can layout text in the given font.
*
* @see LEFontInstance
*
* @stable ICU 2.8
*/
static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
/**
* Override of existing call that provides flags to control typography.
* @stable ICU 3.4
*/
static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
/**
* ICU "poor man's RTTI", returns a UClassID for the actual class.
*
* @stable ICU 2.8
*/
virtual UClassID getDynamicClassID() const;
/**
* ICU "poor man's RTTI", returns a UClassID for this class.
*
* @stable ICU 2.8
*/
static UClassID getStaticClassID();
};
U_NAMESPACE_END
#endif