1/*
2 * (C) Copyright IBM Corp. 1998-2011 - 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    /** @internal Flag to request kerning. */
67    static const le_int32 kTypoFlagKern;
68    /** @internal Flag to request ligatures. */
69    static const le_int32 kTypoFlagLiga;
70
71protected:
72    /**
73     * The object which holds the glyph storage
74     *
75     * @internal
76     */
77    LEGlyphStorage *fGlyphStorage;
78
79    /**
80     * The font instance for the text font.
81     *
82     * @see LEFontInstance
83     *
84     * @internal
85     */
86    const LEFontInstance *fFontInstance;
87
88    /**
89     * The script code for the text
90     *
91     * @see ScriptAndLanguageTags.h for script codes.
92     *
93     * @internal
94     */
95    le_int32 fScriptCode;
96
97    /**
98     * The langauge code for the text
99     *
100     * @see ScriptAndLanguageTags.h for language codes.
101     *
102     * @internal
103     */
104    le_int32 fLanguageCode;
105
106    /**
107     * The typographic control flags
108     *
109     * @internal
110     */
111    le_int32 fTypoFlags;
112
113    /**
114     * <code>TRUE</code> if <code>mapCharsToGlyphs</code> should replace ZWJ / ZWNJ with a glyph
115     * with no contours.
116     *
117     * @internal
118     */
119    le_bool fFilterZeroWidth;
120
121    /**
122     * This constructs an instance for a given font, script and language. Subclass constructors
123     * must call this constructor.
124     *
125     * @param fontInstance - the font for the text
126     * @param scriptCode - the script for the text
127     * @param languageCode - the language for the text
128     * @param typoFlags - the typographic control flags for the text (a bitfield).  Use kTypoFlagKern
129     * if kerning is desired, kTypoFlagLiga if ligature formation is desired.  Others are reserved.
130     * @param success - set to an error code if the operation fails
131     *
132     * @see LEFontInstance
133     * @see ScriptAndLanguageTags.h
134     *
135     * @internal
136     */
137    LayoutEngine(const LEFontInstance *fontInstance,
138                 le_int32 scriptCode,
139                 le_int32 languageCode,
140                 le_int32 typoFlags,
141                 LEErrorCode &success);
142
143    /**
144     * This overrides the default no argument constructor to make it
145     * difficult for clients to call it. Clients are expected to call
146     * layoutEngineFactory.
147     *
148     * @internal
149     */
150    LayoutEngine();
151
152    /**
153     * This method does any required pre-processing to the input characters. It
154     * may generate output characters that differ from the input charcters due to
155     * insertions, deletions, or reorderings. In such cases, it will also generate an
156     * output character index array reflecting these changes.
157     *
158     * Subclasses must override this method.
159     *
160     * Input parameters:
161     * @param chars - the input character context
162     * @param offset - the index of the first character to process
163     * @param count - the number of characters to process
164     * @param max - the number of characters in the input context
165     * @param rightToLeft - TRUE if the characters are in a right to left directional run
166     * @param outChars - the output character array, if different from the input
167     * @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
168     * @param success - set to an error code if the operation fails
169     *
170     * @return the output character count (input character count if no change)
171     *
172     * @internal
173     */
174    virtual le_int32 characterProcessing(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft,
175            LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success);
176
177    /**
178     * This method does the glyph processing. It converts an array of characters
179     * into an array of glyph indices and character indices. The characters to be
180     * processed are passed in a surrounding context. The context is specified as
181     * a starting address and a maximum character count. An offset and a count are
182     * used to specify the characters to be processed.
183     *
184     * The default implementation of this method only does character to glyph mapping.
185     * Subclasses needing more elaborate glyph processing must override this method.
186     *
187     * Input parameters:
188     * @param chars - the character context
189     * @param offset - the offset of the first character to process
190     * @param count - the number of characters to process
191     * @param max - the number of characters in the context.
192     * @param rightToLeft - TRUE if the text is in a right to left directional run
193     * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
194     *                       will be set.
195     *
196     * Output parameters:
197     * @param success - set to an error code if the operation fails
198     *
199     * @return the number of glyphs in the glyph index array
200     *
201     * @internal
202     */
203    virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success);
204
205    /**
206     * This method does basic glyph positioning. The default implementation positions
207     * the glyphs based on their advance widths. This is sufficient for most uses. It
208     * is not expected that many subclasses will override this method.
209     *
210     * Input parameters:
211     * @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
212     * @param x - the starting X position
213     * @param y - the starting Y position
214     * @param success - set to an error code if the operation fails
215     *
216     * @internal
217     */
218    virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
219
220    /**
221     * This method does positioning adjustments like accent positioning and
222     * kerning. The default implementation does nothing. Subclasses needing
223     * position adjustments must override this method.
224     *
225     * Note that this method has both characters and glyphs as input so that
226     * it can use the character codes to determine glyph types if that information
227     * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
228     * table)
229     *
230     * @param chars - the input character context
231     * @param offset - the offset of the first character to process
232     * @param count - the number of characters to process
233     * @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
234     * @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
235     *                       adjusted as needed.
236     * @param success - output parameter set to an error code if the operation fails
237     *
238     * @internal
239     */
240    virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
241
242    /**
243     * This method gets a table from the font associated with
244     * the text. The default implementation gets the table from
245     * the font instance. Subclasses which need to get the tables
246     * some other way must override this method.
247     *
248     * @param tableTag - the four byte table tag.
249     *
250     * @return the address of the table.
251     *
252     * @internal
253     */
254    virtual const void *getFontTable(LETag tableTag) const;
255
256    /**
257     * This method does character to glyph mapping. The default implementation
258     * uses the font instance to do the mapping. It will allocate the glyph and
259     * character index arrays if they're not already allocated. If it allocates the
260     * character index array, it will fill it it.
261     *
262     * This method supports right to left
263     * text with the ability to store the glyphs in reverse order, and by supporting
264     * character mirroring, which will replace a character which has a left and right
265     * form, such as parens, with the opposite form before mapping it to a glyph index.
266     *
267     * Input parameters:
268     * @param chars - the input character context
269     * @param offset - the offset of the first character to be mapped
270     * @param count - the number of characters to be mapped
271     * @param reverse - if <code>TRUE</code>, the output will be in reverse order
272     * @param mirror - if <code>TRUE</code>, do character mirroring
273     * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
274     *                       indices arrays will be filled in.
275     * @param success - set to an error code if the operation fails
276     *
277     * @see LEFontInstance
278     *
279     * @internal
280     */
281    virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
282
283    /**
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     *
287     * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
288     * @param markFilter - used to identify mark glyphs
289     * @param success - output parameter set to an error code if the operation fails
290     *
291     * @see LEGlyphFilter
292     *
293     * @internal
294     */
295    static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
296
297
298    /**
299     * This is a convenience method that forces the advance width of mark
300     * glyphs to be zero, which is required for proper selection and highlighting.
301     * This method uses the input characters to identify marks. This is required in
302     * cases where the font does not contain enough information to identify them based
303     * on the glyph IDs.
304     *
305     * @param chars - the array of input characters
306     * @param charCount - the number of input characers
307     * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
308     * @param reverse - <code>TRUE</code> if the glyph array has been reordered
309     * @param markFilter - used to identify mark glyphs
310     * @param success - output parameter set to an error code if the operation fails
311     *
312     * @see LEGlyphFilter
313     *
314     * @internal
315     */
316    static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
317
318
319public:
320    /**
321     * The destructor. It will free any storage allocated for the
322     * glyph, character index and position arrays by calling the reset
323     * method. It is declared virtual so that it will be invoked by the
324     * subclass destructors.
325     *
326     * @stable ICU 2.8
327     */
328    virtual ~LayoutEngine();
329
330    /**
331     * This method will invoke the layout steps in their correct order by calling
332     * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
333     * compute the glyph, character index and position arrays.
334     *
335     * @param chars - the input character context
336     * @param offset - the offset of the first character to process
337     * @param count - the number of characters to process
338     * @param max - the number of characters in the input context
339     * @param rightToLeft - TRUE if the characers are in a right to left directional run
340     * @param x - the initial X position
341     * @param y - the initial Y position
342     * @param success - output parameter set to an error code if the operation fails
343     *
344     * @return the number of glyphs in the glyph array
345     *
346     * Note: The glyph, character index and position array can be accessed
347     * using the getter methods below.
348     *
349     * Note: If you call this method more than once, you must call the reset()
350     * method first to free the glyph, character index and position arrays
351     * allocated by the previous call.
352     *
353     * @stable ICU 2.8
354     */
355    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);
356
357    /**
358     * This method returns the number of glyphs in the glyph array. Note
359     * that the number of glyphs will be greater than or equal to the number
360     * of characters used to create the LayoutEngine.
361     *
362     * @return the number of glyphs in the glyph array
363     *
364     * @stable ICU 2.8
365     */
366    le_int32 getGlyphCount() const;
367
368    /**
369     * This method copies the glyph array into a caller supplied array.
370     * The caller must ensure that the array is large enough to hold all
371     * the glyphs.
372     *
373     * @param glyphs - the destiniation glyph array
374     * @param success - set to an error code if the operation fails
375     *
376     * @stable ICU 2.8
377     */
378    void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
379
380    /**
381     * This method copies the glyph array into a caller supplied array,
382     * ORing in extra bits. (This functionality is needed by the JDK,
383     * which uses 32 bits pre glyph idex, with the high 16 bits encoding
384     * the composite font slot number)
385     *
386     * @param glyphs - the destination (32 bit) glyph array
387     * @param extraBits - this value will be ORed with each glyph index
388     * @param success - set to an error code if the operation fails
389     *
390     * @stable ICU 2.8
391     */
392    virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
393
394    /**
395     * This method copies the character index array into a caller supplied array.
396     * The caller must ensure that the array is large enough to hold a
397     * character index for each glyph.
398     *
399     * @param charIndices - the destiniation character index array
400     * @param success - set to an error code if the operation fails
401     *
402     * @stable ICU 2.8
403     */
404    void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
405
406    /**
407     * This method copies the character index array into a caller supplied array.
408     * The caller must ensure that the array is large enough to hold a
409     * character index for each glyph.
410     *
411     * @param charIndices - the destiniation character index array
412     * @param indexBase - an offset which will be added to each index
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[], le_int32 indexBase, LEErrorCode &success) const;
418
419    /**
420     * This method copies the position array into a caller supplied array.
421     * The caller must ensure that the array is large enough to hold an
422     * X and Y position for each glyph, plus an extra X and Y for the
423     * advance of the last glyph.
424     *
425     * @param positions - the destiniation position array
426     * @param success - set to an error code if the operation fails
427     *
428     * @stable ICU 2.8
429     */
430    void getGlyphPositions(float positions[], LEErrorCode &success) const;
431
432    /**
433     * This method returns the X and Y position of the glyph at
434     * the given index.
435     *
436     * Input parameters:
437     * @param glyphIndex - the index of the glyph
438     *
439     * Output parameters:
440     * @param x - the glyph's X position
441     * @param y - the glyph's Y position
442     * @param success - set to an error code if the operation fails
443     *
444     * @stable ICU 2.8
445     */
446    void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
447
448    /**
449     * This method frees the glyph, character index and position arrays
450     * so that the LayoutEngine can be reused to layout a different
451     * characer array. (This method is also called by the destructor)
452     *
453     * @stable ICU 2.8
454     */
455    virtual void reset();
456
457    /**
458     * This method returns a LayoutEngine capable of laying out text
459     * in the given font, script and langauge. Note that the LayoutEngine
460     * returned may be a subclass of LayoutEngine.
461     *
462     * @param fontInstance - the font of the text
463     * @param scriptCode - the script of the text
464     * @param languageCode - the language of the text
465     * @param success - output parameter set to an error code if the operation fails
466     *
467     * @return a LayoutEngine which can layout text in the given font.
468     *
469     * @see LEFontInstance
470     *
471     * @stable ICU 2.8
472     */
473    static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
474
475    /**
476     * Override of existing call that provides flags to control typography.
477     * @stable ICU 3.4
478     */
479    static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
480
481    /**
482     * ICU "poor man's RTTI", returns a UClassID for the actual class.
483     *
484     * @stable ICU 2.8
485     */
486    virtual UClassID getDynamicClassID() const;
487
488    /**
489     * ICU "poor man's RTTI", returns a UClassID for this class.
490     *
491     * @stable ICU 2.8
492     */
493    static UClassID getStaticClassID();
494
495};
496
497U_NAMESPACE_END
498#endif
499