icuSources/layout/LayoutEngine.h

   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
  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. */
  68     static const le_int32 kTypoFlagKern;
  69     /** @internal Flag to request ligatures. */
  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      *
 256      * @return the address of the table.
 257      *
 258      * @internal
 259      */
 260     virtual const void *getFontTable(LETag tableTag) const;
 261
 262     /**
 263      * This method does character to glyph mapping. The default implementation
 264      * uses the font instance to do the mapping. It will allocate the glyph and
 265      * character index arrays if they're not already allocated. If it allocates the
 266      * character index array, it will fill it it.
 267      *
 268      * This method supports right to left
 269      * text with the ability to store the glyphs in reverse order, and by supporting
 270      * character mirroring, which will replace a character which has a left and right
 271      * form, such as parens, with the opposite form before mapping it to a glyph index.
 272      *
 273      * Input parameters:
 274      * @param chars - the input character context
 275      * @param offset - the offset of the first character to be mapped
 276      * @param count - the number of characters to be mapped
 277      * @param reverse - if <code>TRUE</code>, the output will be in reverse order
 278      * @param mirror - if <code>TRUE</code>, do character mirroring
 279      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
 280      *                       indices arrays will be filled in.
 281      * @param success - set to an error code if the operation fails
 282      *
 283      * @see LEFontInstance
 284      *
 285      * @internal
 286      */
 287     virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 288
 289 #ifndef U_HIDE_INTERNAL_API
 290     /**
 291      * This is a convenience method that forces the advance width of mark
 292      * glyphs to be zero, which is required for proper selection and highlighting.
 293      *
 294      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 295      * @param markFilter - used to identify mark glyphs
 296      * @param success - output parameter set to an error code if the operation fails
 297      *
 298      * @see LEGlyphFilter
 299      *
 300      * @internal
 301      */
 302     static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 303
 304
 305     /**
 306      * This is a convenience method that forces the advance width of mark
 307      * glyphs to be zero, which is required for proper selection and highlighting.
 308      * This method uses the input characters to identify marks. This is required in
 309      * cases where the font does not contain enough information to identify them based
 310      * on the glyph IDs.
 311      *
 312      * @param chars - the array of input characters
 313      * @param charCount - the number of input characers
 314      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 315      * @param reverse - <code>TRUE</code> if the glyph array has been reordered
 316      * @param markFilter - used to identify mark glyphs
 317      * @param success - output parameter set to an error code if the operation fails
 318      *
 319      * @see LEGlyphFilter
 320      *
 321      * @internal
 322      */
 323     static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 324 #endif  /* U_HIDE_INTERNAL_API */
 325
 326 public:
 327     /**
 328      * The destructor. It will free any storage allocated for the
 329      * glyph, character index and position arrays by calling the reset
 330      * method. It is declared virtual so that it will be invoked by the
 331      * subclass destructors.
 332      *
 333      * @stable ICU 2.8
 334      */
 335     virtual ~LayoutEngine();
 336
 337     /**
 338      * This method will invoke the layout steps in their correct order by calling
 339      * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
 340      * compute the glyph, character index and position arrays.
 341      *
 342      * @param chars - the input character context
 343      * @param offset - the offset of the first character to process
 344      * @param count - the number of characters to process
 345      * @param max - the number of characters in the input context
 346      * @param rightToLeft - TRUE if the characers are in a right to left directional run
 347      * @param x - the initial X position
 348      * @param y - the initial Y position
 349      * @param success - output parameter set to an error code if the operation fails
 350      *
 351      * @return the number of glyphs in the glyph array
 352      *
 353      * Note: The glyph, character index and position array can be accessed
 354      * using the getter methods below.
 355      *
 356      * Note: If you call this method more than once, you must call the reset()
 357      * method first to free the glyph, character index and position arrays
 358      * allocated by the previous call.
 359      *
 360      * @stable ICU 2.8
 361      */
 362     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);
 363
 364     /**
 365      * This method returns the number of glyphs in the glyph array. Note
 366      * that the number of glyphs will be greater than or equal to the number
 367      * of characters used to create the LayoutEngine.
 368      *
 369      * @return the number of glyphs in the glyph array
 370      *
 371      * @stable ICU 2.8
 372      */
 373     le_int32 getGlyphCount() const;
 374
 375     /**
 376      * This method copies the glyph array into a caller supplied array.
 377      * The caller must ensure that the array is large enough to hold all
 378      * the glyphs.
 379      *
 380      * @param glyphs - the destiniation glyph array
 381      * @param success - set to an error code if the operation fails
 382      *
 383      * @stable ICU 2.8
 384      */
 385     void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
 386
 387     /**
 388      * This method copies the glyph array into a caller supplied array,
 389      * ORing in extra bits. (This functionality is needed by the JDK,
 390      * which uses 32 bits pre glyph idex, with the high 16 bits encoding
 391      * the composite font slot number)
 392      *
 393      * @param glyphs - the destination (32 bit) glyph array
 394      * @param extraBits - this value will be ORed with each glyph index
 395      * @param success - set to an error code if the operation fails
 396      *
 397      * @stable ICU 2.8
 398      */
 399     virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
 400
 401     /**
 402      * This method copies the character index array into a caller supplied array.
 403      * The caller must ensure that the array is large enough to hold a
 404      * character index for each glyph.
 405      *
 406      * @param charIndices - the destiniation character index array
 407      * @param success - set to an error code if the operation fails
 408      *
 409      * @stable ICU 2.8
 410      */
 411     void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
 412
 413     /**
 414      * This method copies the character index array into a caller supplied array.
 415      * The caller must ensure that the array is large enough to hold a
 416      * character index for each glyph.
 417      *
 418      * @param charIndices - the destiniation character index array
 419      * @param indexBase - an offset which will be added to each index
 420      * @param success - set to an error code if the operation fails
 421      *
 422      * @stable ICU 2.8
 423      */
 424     void getCharIndices(le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const;
 425
 426     /**
 427      * This method copies the position array into a caller supplied array.
 428      * The caller must ensure that the array is large enough to hold an
 429      * X and Y position for each glyph, plus an extra X and Y for the
 430      * advance of the last glyph.
 431      *
 432      * @param positions - the destiniation position array
 433      * @param success - set to an error code if the operation fails
 434      *
 435      * @stable ICU 2.8
 436      */
 437     void getGlyphPositions(float positions[], LEErrorCode &success) const;
 438
 439     /**
 440      * This method returns the X and Y position of the glyph at
 441      * the given index.
 442      *
 443      * Input parameters:
 444      * @param glyphIndex - the index of the glyph
 445      *
 446      * Output parameters:
 447      * @param x - the glyph's X position
 448      * @param y - the glyph's Y position
 449      * @param success - set to an error code if the operation fails
 450      *
 451      * @stable ICU 2.8
 452      */
 453     void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
 454
 455     /**
 456      * This method frees the glyph, character index and position arrays
 457      * so that the LayoutEngine can be reused to layout a different
 458      * characer array. (This method is also called by the destructor)
 459      *
 460      * @stable ICU 2.8
 461      */
 462     virtual void reset();
 463
 464     /**
 465      * This method returns a LayoutEngine capable of laying out text
 466      * in the given font, script and langauge. Note that the LayoutEngine
 467      * returned may be a subclass of LayoutEngine.
 468      *
 469      * @param fontInstance - the font of the text
 470      * @param scriptCode - the script of the text
 471      * @param languageCode - the language of the text
 472      * @param success - output parameter set to an error code if the operation fails
 473      *
 474      * @return a LayoutEngine which can layout text in the given font.
 475      *
 476      * @see LEFontInstance
 477      *
 478      * @stable ICU 2.8
 479      */
 480     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
 481
 482     /**
 483      * Override of existing call that provides flags to control typography.
 484      * @stable ICU 3.4
 485      */
 486     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
 487
 488     /**
 489      * ICU "poor man's RTTI", returns a UClassID for the actual class.
 490      *
 491      * @stable ICU 2.8
 492      */
 493     virtual UClassID getDynamicClassID() const;
 494
 495     /**
 496      * ICU "poor man's RTTI", returns a UClassID for this class.
 497      *
 498      * @stable ICU 2.8
 499      */
 500     static UClassID getStaticClassID();
 501
 502 };
 503
 504 U_NAMESPACE_END
 505 #endif