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
15U_NAMESPACE_BEGIN
16
17class LEFontInstance;
18class LEGlyphFilter;
19class 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 */
64class U_LAYOUT_API LayoutEngine : public UObject {
65public:
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
73protected:
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     */
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
332public:
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
510U_NAMESPACE_END
511#endif
512