4 * (C) Copyright IBM Corp. 1998-2006 - All Rights Reserved
8 #ifndef __LAYOUTENGINE_H
9 #define __LAYOUTENGINE_H
15 * \brief C++ API: Virtual base class for complex text layout.
25 * This is a virtual base class used to do complex text layout. The text must all
26 * be in a single font, script, and language. An instance of a LayoutEngine can be
27 * created by calling the layoutEngineFactory method. Fonts are identified by
28 * instances of the LEFontInstance class. Script and language codes are identified
29 * by integer codes, which are defined in ScriptAndLanuageTags.h.
31 * Note that this class is not public API. It is declared public so that it can be
32 * exported from the library that it is a part of.
34 * The input to the layout process is an array of characters in logical order,
35 * and a starting X, Y position for the text. The output is an array of glyph indices,
36 * an array of character indices for the glyphs, and an array of glyph positions.
37 * These arrays are protected members of LayoutEngine which can be retreived by a
38 * public method. The reset method can be called to free these arrays so that the
39 * LayoutEngine can be reused.
41 * The layout process is done in three steps. There is a protected virtual method
42 * for each step. These methods have a default implementation which only does
43 * character to glyph mapping and default positioning using the glyph's advance
44 * widths. Subclasses can override these methods for more advanced layout.
45 * There is a public method which invokes the steps in the correct order.
49 * 1) Glyph processing - character to glyph mapping and any other glyph processing
50 * such as ligature substitution and contextual forms.
52 * 2) Glyph positioning - position the glyphs based on their advance widths.
54 * 3) Glyph position adjustments - adjustment of glyph positions for kerning,
55 * accent placement, etc.
57 * NOTE: in all methods below, output parameters are references to pointers so
58 * the method can allocate and free the storage as needed. All storage allocated
59 * in this way is owned by the object which created it, and will be freed when it
60 * is no longer needed, or when the object's destructor is invoked.
63 * @see ScriptAndLanguageTags.h
67 class U_LAYOUT_API LayoutEngine
: public UObject
{
70 * The object which holds the glyph storage
74 LEGlyphStorage
*fGlyphStorage
;
77 * The font instance for the text font.
83 const LEFontInstance
*fFontInstance
;
86 * The script code for the text
88 * @see ScriptAndLanguageTags.h for script codes.
95 * The langauge code for the text
97 * @see ScriptAndLanguageTags.h for language codes.
101 le_int32 fLanguageCode
;
104 * The typographic control flags
111 * This constructs an instance for a given font, script and language. Subclass constructors
112 * must call this constructor.
114 * @param fontInstance - the font for the text
115 * @param scriptCode - the script for the text
116 * @param languageCode - the language for the text
117 * @param typoFlags - the typographic control flags for the text. Set bit 1 if kerning
118 * is desired, set bit 2 if ligature formation is desired. Others are reserved.
120 * @see LEFontInstance
121 * @see ScriptAndLanguageTags.h
125 LayoutEngine(const LEFontInstance
*fontInstance
, le_int32 scriptCode
, le_int32 languageCode
, le_int32 typoFlags
);
128 * This overrides the default no argument constructor to make it
129 * difficult for clients to call it. Clients are expected to call
130 * layoutEngineFactory.
137 * This method does any required pre-processing to the input characters. It
138 * may generate output characters that differ from the input charcters due to
139 * insertions, deletions, or reorderings. In such cases, it will also generate an
140 * output character index array reflecting these changes.
142 * Subclasses must override this method.
145 * @param chars - the input character context
146 * @param offset - the index of the first character to process
147 * @param count - the number of characters to process
148 * @param max - the number of characters in the input context
149 * @param rightToLeft - TRUE if the characters are in a right to left directional run
150 * @param outChars - the output character array, if different from the input
151 * @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
152 * @param success - set to an error code if the operation fails
154 * @return the output character count (input character count if no change)
158 virtual le_int32
characterProcessing(const LEUnicode chars
[], le_int32 offset
, le_int32 count
, le_int32 max
, le_bool rightToLeft
,
159 LEUnicode
*&outChars
, LEGlyphStorage
&glyphStorage
, LEErrorCode
&success
);
162 * This method does the glyph processing. It converts an array of characters
163 * into an array of glyph indices and character indices. The characters to be
164 * processed are passed in a surrounding context. The context is specified as
165 * a starting address and a maximum character count. An offset and a count are
166 * used to specify the characters to be processed.
168 * The default implementation of this method only does character to glyph mapping.
169 * Subclasses needing more elaborate glyph processing must override this method.
172 * @param chars - the character context
173 * @param offset - the offset of the first character to process
174 * @param count - the number of characters to process
175 * @param max - the number of characters in the context.
176 * @param rightToLeft - TRUE if the text is in a right to left directional run
177 * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
181 * @param success - set to an error code if the operation fails
183 * @return the number of glyphs in the glyph index array
187 virtual le_int32
computeGlyphs(const LEUnicode chars
[], le_int32 offset
, le_int32 count
, le_int32 max
, le_bool rightToLeft
, LEGlyphStorage
&glyphStorage
, LEErrorCode
&success
);
190 * This method does basic glyph positioning. The default implementation positions
191 * the glyphs based on their advance widths. This is sufficient for most uses. It
192 * is not expected that many subclasses will override this method.
195 * @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
196 * @param x - the starting X position
197 * @param y - the starting Y position
198 * @param success - set to an error code if the operation fails
202 virtual void positionGlyphs(LEGlyphStorage
&glyphStorage
, float x
, float y
, LEErrorCode
&success
);
205 * This method does positioning adjustments like accent positioning and
206 * kerning. The default implementation does nothing. Subclasses needing
207 * position adjustments must override this method.
209 * Note that this method has both characters and glyphs as input so that
210 * it can use the character codes to determine glyph types if that information
211 * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
214 * @param chars - the input character context
215 * @param offset - the offset of the first character to process
216 * @param count - the number of characters to process
217 * @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
218 * @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
219 * adjusted as needed.
220 * @param success - output parameter set to an error code if the operation fails
224 virtual void adjustGlyphPositions(const LEUnicode chars
[], le_int32 offset
, le_int32 count
, le_bool reverse
, LEGlyphStorage
&glyphStorage
, LEErrorCode
&success
);
227 * This method gets a table from the font associated with
228 * the text. The default implementation gets the table from
229 * the font instance. Subclasses which need to get the tables
230 * some other way must override this method.
232 * @param tableTag - the four byte table tag.
234 * @return the address of the table.
238 virtual const void *getFontTable(LETag tableTag
) const;
241 * This method does character to glyph mapping. The default implementation
242 * uses the font instance to do the mapping. It will allocate the glyph and
243 * character index arrays if they're not already allocated. If it allocates the
244 * character index array, it will fill it it.
246 * This method supports right to left
247 * text with the ability to store the glyphs in reverse order, and by supporting
248 * character mirroring, which will replace a character which has a left and right
249 * form, such as parens, with the opposite form before mapping it to a glyph index.
252 * @param chars - the input character context
253 * @param offset - the offset of the first character to be mapped
254 * @param count - the number of characters to be mapped
255 * @param reverse - if <code>TRUE</code>, the output will be in reverse order
256 * @param mirror - if <code>TRUE</code>, do character mirroring
257 * @param filterZeroWidth - if <code>TRUE</code> replace ZWJ / ZWNJ with a glyph with no contours.
258 * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
259 * indices arrays will be filled in.
260 * @param success - set to an error code if the operation fails
262 * @see LEFontInstance
266 virtual void mapCharsToGlyphs(const LEUnicode chars
[], le_int32 offset
, le_int32 count
, le_bool reverse
, le_bool mirror
, le_bool filterZeroWidth
, LEGlyphStorage
&glyphStorage
, LEErrorCode
&success
);
269 * This is a convenience method that forces the advance width of mark
270 * glyphs to be zero, which is required for proper selection and highlighting.
272 * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
273 * @param markFilter - used to identify mark glyphs
274 * @param success - output parameter set to an error code if the operation fails
280 static void adjustMarkGlyphs(LEGlyphStorage
&glyphStorage
, LEGlyphFilter
*markFilter
, LEErrorCode
&success
);
284 * This is a convenience method that forces the advance width of mark
285 * glyphs to be zero, which is required for proper selection and highlighting.
286 * This method uses the input characters to identify marks. This is required in
287 * cases where the font does not contain enough information to identify them based
290 * @param chars - the array of input characters
291 * @param charCount - the number of input characers
292 * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
293 * @param reverse - <code>TRUE</code> if the glyph array has been reordered
294 * @param markFilter - used to identify mark glyphs
295 * @param success - output parameter set to an error code if the operation fails
301 static void adjustMarkGlyphs(const LEUnicode chars
[], le_int32 charCount
, le_bool reverse
, LEGlyphStorage
&glyphStorage
, LEGlyphFilter
*markFilter
, LEErrorCode
&success
);
306 * The destructor. It will free any storage allocated for the
307 * glyph, character index and position arrays by calling the reset
308 * method. It is declared virtual so that it will be invoked by the
309 * subclass destructors.
313 virtual ~LayoutEngine();
316 * This method will invoke the layout steps in their correct order by calling
317 * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
318 * compute the glyph, character index and position arrays.
320 * @param chars - the input character context
321 * @param offset - the offset of the first character to process
322 * @param count - the number of characters to process
323 * @param max - the number of characters in the input context
324 * @param rightToLeft - TRUE if the characers are in a right to left directional run
325 * @param x - the initial X position
326 * @param y - the initial Y position
327 * @param success - output parameter set to an error code if the operation fails
329 * @return the number of glyphs in the glyph array
331 * Note: The glyph, character index and position array can be accessed
332 * using the getter methods below.
334 * Note: If you call this method more than once, you must call the reset()
335 * method first to free the glyph, character index and position arrays
336 * allocated by the previous call.
340 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
);
343 * This method returns the number of glyphs in the glyph array. Note
344 * that the number of glyphs will be greater than or equal to the number
345 * of characters used to create the LayoutEngine.
347 * @return the number of glyphs in the glyph array
351 le_int32
getGlyphCount() const;
354 * This method copies the glyph array into a caller supplied array.
355 * The caller must ensure that the array is large enough to hold all
358 * @param glyphs - the destiniation glyph array
359 * @param success - set to an error code if the operation fails
363 void getGlyphs(LEGlyphID glyphs
[], LEErrorCode
&success
) const;
366 * This method copies the glyph array into a caller supplied array,
367 * ORing in extra bits. (This functionality is needed by the JDK,
368 * which uses 32 bits pre glyph idex, with the high 16 bits encoding
369 * the composite font slot number)
371 * @param glyphs - the destination (32 bit) glyph array
372 * @param extraBits - this value will be ORed with each glyph index
373 * @param success - set to an error code if the operation fails
377 virtual void getGlyphs(le_uint32 glyphs
[], le_uint32 extraBits
, LEErrorCode
&success
) const;
380 * This method copies the character index array into a caller supplied array.
381 * The caller must ensure that the array is large enough to hold a
382 * character index for each glyph.
384 * @param charIndices - the destiniation character index array
385 * @param success - set to an error code if the operation fails
389 void getCharIndices(le_int32 charIndices
[], LEErrorCode
&success
) const;
392 * This method copies the character index array into a caller supplied array.
393 * The caller must ensure that the array is large enough to hold a
394 * character index for each glyph.
396 * @param charIndices - the destiniation character index array
397 * @param indexBase - an offset which will be added to each index
398 * @param success - set to an error code if the operation fails
402 void getCharIndices(le_int32 charIndices
[], le_int32 indexBase
, LEErrorCode
&success
) const;
405 * This method copies the position array into a caller supplied array.
406 * The caller must ensure that the array is large enough to hold an
407 * X and Y position for each glyph, plus an extra X and Y for the
408 * advance of the last glyph.
410 * @param positions - the destiniation position array
411 * @param success - set to an error code if the operation fails
415 void getGlyphPositions(float positions
[], LEErrorCode
&success
) const;
418 * This method returns the X and Y position of the glyph at
422 * @param glyphIndex - the index of the glyph
425 * @param x - the glyph's X position
426 * @param y - the glyph's Y position
427 * @param success - set to an error code if the operation fails
431 void getGlyphPosition(le_int32 glyphIndex
, float &x
, float &y
, LEErrorCode
&success
) const;
434 * This method frees the glyph, character index and position arrays
435 * so that the LayoutEngine can be reused to layout a different
436 * characer array. (This method is also called by the destructor)
440 virtual void reset();
443 * This method returns a LayoutEngine capable of laying out text
444 * in the given font, script and langauge. Note that the LayoutEngine
445 * returned may be a subclass of LayoutEngine.
447 * @param fontInstance - the font of the text
448 * @param scriptCode - the script of the text
449 * @param languageCode - the language of the text
450 * @param success - output parameter set to an error code if the operation fails
452 * @return a LayoutEngine which can layout text in the given font.
454 * @see LEFontInstance
458 static LayoutEngine
*layoutEngineFactory(const LEFontInstance
*fontInstance
, le_int32 scriptCode
, le_int32 languageCode
, LEErrorCode
&success
);
461 * Override of existing call that provides flags to control typography.
464 static LayoutEngine
*layoutEngineFactory(const LEFontInstance
*fontInstance
, le_int32 scriptCode
, le_int32 languageCode
, le_int32 typo_flags
, LEErrorCode
&success
);
467 * ICU "poor man's RTTI", returns a UClassID for the actual class.
471 virtual UClassID
getDynamicClassID() const;
474 * ICU "poor man's RTTI", returns a UClassID for this class.
478 static UClassID
getStaticClassID();