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1 /*
2  * (C) Copyright IBM Corp. and others 1998-2013 - All Rights Reserved
3  */
4 
5 #ifndef __LAYOUTENGINE_H
6 #define __LAYOUTENGINE_H
7 
8 #include "LETypes.h"
9 
10 /**
11  * \file
12  * \brief C++ API: Virtual base class for complex text layout.
13  */
14 
15 U_NAMESPACE_BEGIN
16 
17 class LEFontInstance;
18 class LEGlyphFilter;
19 class LEGlyphStorage;
20 
21 /**
22  * This is a virtual base class used to do complex text layout. The text must all
23  * be in a single font, script, and language. An instance of a LayoutEngine can be
24  * created by calling the layoutEngineFactory method. Fonts are identified by
25  * instances of the LEFontInstance class. Script and language codes are identified
26  * by integer codes, which are defined in ScriptAndLanuageTags.h.
27  *
28  * Note that this class is not public API. It is declared public so that it can be
29  * exported from the library that it is a part of.
30  *
31  * The input to the layout process is an array of characters in logical order,
32  * and a starting X, Y position for the text. The output is an array of glyph indices,
33  * an array of character indices for the glyphs, and an array of glyph positions.
34  * These arrays are protected members of LayoutEngine which can be retreived by a
35  * public method. The reset method can be called to free these arrays so that the
36  * LayoutEngine can be reused.
37  *
38  * The layout process is done in three steps. There is a protected virtual method
39  * for each step. These methods have a default implementation which only does
40  * character to glyph mapping and default positioning using the glyph's advance
41  * widths. Subclasses can override these methods for more advanced layout.
42  * There is a public method which invokes the steps in the correct order.
43  *
44  * The steps are:
45  *
46  * 1) Glyph processing - character to glyph mapping and any other glyph processing
47  *    such as ligature substitution and contextual forms.
48  *
49  * 2) Glyph positioning - position the glyphs based on their advance widths.
50  *
51  * 3) Glyph position adjustments - adjustment of glyph positions for kerning,
52  *    accent placement, etc.
53  *
54  * NOTE: in all methods below, output parameters are references to pointers so
55  * the method can allocate and free the storage as needed. All storage allocated
56  * in this way is owned by the object which created it, and will be freed when it
57  * is no longer needed, or when the object's destructor is invoked.
58  *
59  * @see LEFontInstance
60  * @see ScriptAndLanguageTags.h
61  *
62  * @stable ICU 2.8
63  */
64 class U_LAYOUT_API LayoutEngine : public UObject {
65 public:
66 #ifndef U_HIDE_INTERNAL_API
67     /** @internal Flag to request kerning. Use LE_Kerning_FEATURE_FLAG instead. */
68     static const le_int32 kTypoFlagKern;
69     /** @internal Flag to request ligatures. Use LE_Ligatures_FEATURE_FLAG instead. */
70     static const le_int32 kTypoFlagLiga;
71 #endif  /* U_HIDE_INTERNAL_API */
72 
73 protected:
74     /**
75      * The object which holds the glyph storage
76      *
77      * @internal
78      */
79     LEGlyphStorage *fGlyphStorage;
80 
81     /**
82      * The font instance for the text font.
83      *
84      * @see LEFontInstance
85      *
86      * @internal
87      */
88     const LEFontInstance *fFontInstance;
89 
90     /**
91      * The script code for the text
92      *
93      * @see ScriptAndLanguageTags.h for script codes.
94      *
95      * @internal
96      */
97     le_int32 fScriptCode;
98 
99     /**
100      * The langauge code for the text
101      *
102      * @see ScriptAndLanguageTags.h for language codes.
103      *
104      * @internal
105      */
106     le_int32 fLanguageCode;
107 
108     /**
109      * The typographic control flags
110      *
111      * @internal
112      */
113     le_int32 fTypoFlags;
114 
115     /**
116      * <code>TRUE</code> if <code>mapCharsToGlyphs</code> should replace ZWJ / ZWNJ with a glyph
117      * with no contours.
118      *
119      * @internal
120      */
121     le_bool fFilterZeroWidth;
122 
123 #ifndef U_HIDE_INTERNAL_API
124     /**
125      * This constructs an instance for a given font, script and language. Subclass constructors
126      * must call this constructor.
127      *
128      * @param fontInstance - the font for the text
129      * @param scriptCode - the script for the text
130      * @param languageCode - the language for the text
131      * @param typoFlags - the typographic control flags for the text (a bitfield).  Use kTypoFlagKern
132      * if kerning is desired, kTypoFlagLiga if ligature formation is desired.  Others are reserved.
133      * @param success - set to an error code if the operation fails
134      *
135      * @see LEFontInstance
136      * @see ScriptAndLanguageTags.h
137      *
138      * @internal
139      */
140     LayoutEngine(const LEFontInstance *fontInstance,
141                  le_int32 scriptCode,
142                  le_int32 languageCode,
143                  le_int32 typoFlags,
144                  LEErrorCode &success);
145 #endif  /* U_HIDE_INTERNAL_API */
146 
147     // Do not enclose the protected default constructor with #ifndef U_HIDE_INTERNAL_API
148     // or else the compiler will create a public default constructor.
149     /**
150      * This overrides the default no argument constructor to make it
151      * difficult for clients to call it. Clients are expected to call
152      * layoutEngineFactory.
153      *
154      * @internal
155      */
156     LayoutEngine();
157 
158     /**
159      * This method does any required pre-processing to the input characters. It
160      * may generate output characters that differ from the input charcters due to
161      * insertions, deletions, or reorderings. In such cases, it will also generate an
162      * output character index array reflecting these changes.
163      *
164      * Subclasses must override this method.
165      *
166      * Input parameters:
167      * @param chars - the input character context
168      * @param offset - the index of the first character to process
169      * @param count - the number of characters to process
170      * @param max - the number of characters in the input context
171      * @param rightToLeft - TRUE if the characters are in a right to left directional run
172      * @param outChars - the output character array, if different from the input
173      * @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
174      * @param success - set to an error code if the operation fails
175      *
176      * @return the output character count (input character count if no change)
177      *
178      * @internal
179      */
180     virtual le_int32 characterProcessing(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft,
181             LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success);
182 
183     /**
184      * This method does the glyph processing. It converts an array of characters
185      * into an array of glyph indices and character indices. The characters to be
186      * processed are passed in a surrounding context. The context is specified as
187      * a starting address and a maximum character count. An offset and a count are
188      * used to specify the characters to be processed.
189      *
190      * The default implementation of this method only does character to glyph mapping.
191      * Subclasses needing more elaborate glyph processing must override this method.
192      *
193      * Input parameters:
194      * @param chars - the character context
195      * @param offset - the offset of the first character to process
196      * @param count - the number of characters to process
197      * @param max - the number of characters in the context.
198      * @param rightToLeft - TRUE if the text is in a right to left directional run
199      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
200      *                       will be set.
201      *
202      * Output parameters:
203      * @param success - set to an error code if the operation fails
204      *
205      * @return the number of glyphs in the glyph index array
206      *
207      * @internal
208      */
209     virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success);
210 
211     /**
212      * This method does basic glyph positioning. The default implementation positions
213      * the glyphs based on their advance widths. This is sufficient for most uses. It
214      * is not expected that many subclasses will override this method.
215      *
216      * Input parameters:
217      * @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
218      * @param x - the starting X position
219      * @param y - the starting Y position
220      * @param success - set to an error code if the operation fails
221      *
222      * @internal
223      */
224     virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
225 
226     /**
227      * This method does positioning adjustments like accent positioning and
228      * kerning. The default implementation does nothing. Subclasses needing
229      * position adjustments must override this method.
230      *
231      * Note that this method has both characters and glyphs as input so that
232      * it can use the character codes to determine glyph types if that information
233      * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
234      * table)
235      *
236      * @param chars - the input character context
237      * @param offset - the offset of the first character to process
238      * @param count - the number of characters to process
239      * @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
240      * @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
241      *                       adjusted as needed.
242      * @param success - output parameter set to an error code if the operation fails
243      *
244      * @internal
245      */
246     virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
247 
248     /**
249      * This method gets a table from the font associated with
250      * the text. The default implementation gets the table from
251      * the font instance. Subclasses which need to get the tables
252      * some other way must override this method.
253      *
254      * @param tableTag - the four byte table tag.
255      * @param length - length to use
256      *
257      * @return the address of the table.
258      *
259      * @internal
260      */
261     virtual const void *getFontTable(LETag tableTag, size_t &length) const;
262 
263     /**
264      * @deprecated
265      */
getFontTable(LETag tableTag)266     virtual const void *getFontTable(LETag tableTag) const { size_t ignored; return getFontTable(tableTag, ignored); }
267 
268     /**
269      * This method does character to glyph mapping. The default implementation
270      * uses the font instance to do the mapping. It will allocate the glyph and
271      * character index arrays if they're not already allocated. If it allocates the
272      * character index array, it will fill it it.
273      *
274      * This method supports right to left
275      * text with the ability to store the glyphs in reverse order, and by supporting
276      * character mirroring, which will replace a character which has a left and right
277      * form, such as parens, with the opposite form before mapping it to a glyph index.
278      *
279      * Input parameters:
280      * @param chars - the input character context
281      * @param offset - the offset of the first character to be mapped
282      * @param count - the number of characters to be mapped
283      * @param reverse - if <code>TRUE</code>, the output will be in reverse order
284      * @param mirror - if <code>TRUE</code>, do character mirroring
285      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
286      *                       indices arrays will be filled in.
287      * @param success - set to an error code if the operation fails
288      *
289      * @see LEFontInstance
290      *
291      * @internal
292      */
293     virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
294 
295 #ifndef U_HIDE_INTERNAL_API
296     /**
297      * This is a convenience method that forces the advance width of mark
298      * glyphs to be zero, which is required for proper selection and highlighting.
299      *
300      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
301      * @param markFilter - used to identify mark glyphs
302      * @param success - output parameter set to an error code if the operation fails
303      *
304      * @see LEGlyphFilter
305      *
306      * @internal
307      */
308     static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
309 
310 
311     /**
312      * This is a convenience method that forces the advance width of mark
313      * glyphs to be zero, which is required for proper selection and highlighting.
314      * This method uses the input characters to identify marks. This is required in
315      * cases where the font does not contain enough information to identify them based
316      * on the glyph IDs.
317      *
318      * @param chars - the array of input characters
319      * @param charCount - the number of input characers
320      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
321      * @param reverse - <code>TRUE</code> if the glyph array has been reordered
322      * @param markFilter - used to identify mark glyphs
323      * @param success - output parameter set to an error code if the operation fails
324      *
325      * @see LEGlyphFilter
326      *
327      * @internal
328      */
329     static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
330 #endif  /* U_HIDE_INTERNAL_API */
331 
332 public:
333     /**
334      * The destructor. It will free any storage allocated for the
335      * glyph, character index and position arrays by calling the reset
336      * method. It is declared virtual so that it will be invoked by the
337      * subclass destructors.
338      *
339      * @stable ICU 2.8
340      */
341     virtual ~LayoutEngine();
342 
343     /**
344      * This method will invoke the layout steps in their correct order by calling
345      * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
346      * compute the glyph, character index and position arrays.
347      *
348      * @param chars - the input character context
349      * @param offset - the offset of the first character to process
350      * @param count - the number of characters to process
351      * @param max - the number of characters in the input context
352      * @param rightToLeft - TRUE if the characers are in a right to left directional run
353      * @param x - the initial X position
354      * @param y - the initial Y position
355      * @param success - output parameter set to an error code if the operation fails
356      *
357      * @return the number of glyphs in the glyph array
358      *
359      * Note: The glyph, character index and position array can be accessed
360      * using the getter methods below.
361      *
362      * Note: If you call this method more than once, you must call the reset()
363      * method first to free the glyph, character index and position arrays
364      * allocated by the previous call.
365      *
366      * @stable ICU 2.8
367      */
368     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);
369 
370     /**
371      * This method returns the number of glyphs in the glyph array. Note
372      * that the number of glyphs will be greater than or equal to the number
373      * of characters used to create the LayoutEngine.
374      *
375      * @return the number of glyphs in the glyph array
376      *
377      * @stable ICU 2.8
378      */
379     le_int32 getGlyphCount() const;
380 
381     /**
382      * This method copies the glyph array into a caller supplied array.
383      * The caller must ensure that the array is large enough to hold all
384      * the glyphs.
385      *
386      * @param glyphs - the destiniation glyph array
387      * @param success - set to an error code if the operation fails
388      *
389      * @stable ICU 2.8
390      */
391     void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
392 
393     /**
394      * This method copies the glyph array into a caller supplied array,
395      * ORing in extra bits. (This functionality is needed by the JDK,
396      * which uses 32 bits pre glyph idex, with the high 16 bits encoding
397      * the composite font slot number)
398      *
399      * @param glyphs - the destination (32 bit) glyph array
400      * @param extraBits - this value will be ORed with each glyph index
401      * @param success - set to an error code if the operation fails
402      *
403      * @stable ICU 2.8
404      */
405     virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
406 
407     /**
408      * This method copies the character index array into a caller supplied array.
409      * The caller must ensure that the array is large enough to hold a
410      * character index for each glyph.
411      *
412      * @param charIndices - the destiniation character index array
413      * @param success - set to an error code if the operation fails
414      *
415      * @stable ICU 2.8
416      */
417     void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
418 
419     /**
420      * This method copies the character index array into a caller supplied array.
421      * The caller must ensure that the array is large enough to hold a
422      * character index for each glyph.
423      *
424      * @param charIndices - the destiniation character index array
425      * @param indexBase - an offset which will be added to each index
426      * @param success - set to an error code if the operation fails
427      *
428      * @stable ICU 2.8
429      */
430     void getCharIndices(le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const;
431 
432     /**
433      * This method copies the position array into a caller supplied array.
434      * The caller must ensure that the array is large enough to hold an
435      * X and Y position for each glyph, plus an extra X and Y for the
436      * advance of the last glyph.
437      *
438      * @param positions - the destiniation position array
439      * @param success - set to an error code if the operation fails
440      *
441      * @stable ICU 2.8
442      */
443     void getGlyphPositions(float positions[], LEErrorCode &success) const;
444 
445     /**
446      * This method returns the X and Y position of the glyph at
447      * the given index.
448      *
449      * Input parameters:
450      * @param glyphIndex - the index of the glyph
451      *
452      * Output parameters:
453      * @param x - the glyph's X position
454      * @param y - the glyph's Y position
455      * @param success - set to an error code if the operation fails
456      *
457      * @stable ICU 2.8
458      */
459     void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
460 
461     /**
462      * This method frees the glyph, character index and position arrays
463      * so that the LayoutEngine can be reused to layout a different
464      * characer array. (This method is also called by the destructor)
465      *
466      * @stable ICU 2.8
467      */
468     virtual void reset();
469 
470     /**
471      * This method returns a LayoutEngine capable of laying out text
472      * in the given font, script and langauge. Note that the LayoutEngine
473      * returned may be a subclass of LayoutEngine.
474      *
475      * @param fontInstance - the font of the text
476      * @param scriptCode - the script of the text
477      * @param languageCode - the language of the text
478      * @param success - output parameter set to an error code if the operation fails
479      *
480      * @return a LayoutEngine which can layout text in the given font.
481      *
482      * @see LEFontInstance
483      *
484      * @stable ICU 2.8
485      */
486     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
487 
488     /**
489      * Override of existing call that provides flags to control typography.
490      * @stable ICU 3.4
491      */
492     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
493 
494     /**
495      * ICU "poor man's RTTI", returns a UClassID for the actual class.
496      *
497      * @stable ICU 2.8
498      */
499     virtual UClassID getDynamicClassID() const;
500 
501     /**
502      * ICU "poor man's RTTI", returns a UClassID for this class.
503      *
504      * @stable ICU 2.8
505      */
506     static UClassID getStaticClassID();
507 
508 };
509 
510 U_NAMESPACE_END
511 #endif
512