icuSources/layout/LayoutEngine.h

   1
   2 /*
   3  *
   4  * (C) Copyright IBM Corp. 1998-2007 - All Rights Reserved
   5  *
   6  */
   7
   8 #ifndef __LAYOUTENGINE_H
   9 #define __LAYOUTENGINE_H
  10
  11 #include "LETypes.h"
  12
  13 /**
  14  * \file
  15  * \brief C++ API: Virtual base class for complex text layout.
  16  */
  17
  18 U_NAMESPACE_BEGIN
  19
  20 class LEFontInstance;
  21 class LEGlyphFilter;
  22 class LEGlyphStorage;
  23
  24 /**
  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.
  30  *
  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.
  33  *
  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.
  40  *
  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.
  46  *
  47  * The steps are:
  48  *
  49  * 1) Glyph processing - character to glyph mapping and any other glyph processing
  50  *    such as ligature substitution and contextual forms.
  51  *
  52  * 2) Glyph positioning - position the glyphs based on their advance widths.
  53  *
  54  * 3) Glyph position adjustments - adjustment of glyph positions for kerning,
  55  *    accent placement, etc.
  56  *
  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.
  61  *
  62  * @see LEFontInstance
  63  * @see ScriptAndLanguageTags.h
  64  *
  65  * @stable ICU 2.8
  66  */
  67 class U_LAYOUT_API LayoutEngine : public UObject {
  68 protected:
  69     /**
  70      * The object which holds the glyph storage
  71      *
  72      * @internal
  73      */
  74     LEGlyphStorage *fGlyphStorage;
  75
  76     /**
  77      * The font instance for the text font.
  78      *
  79      * @see LEFontInstance
  80      *
  81      * @internal
  82      */
  83     const LEFontInstance *fFontInstance;
  84
  85     /**
  86      * The script code for the text
  87      *
  88      * @see ScriptAndLanguageTags.h for script codes.
  89      *
  90      * @internal
  91      */
  92     le_int32 fScriptCode;
  93
  94     /**
  95      * The langauge code for the text
  96      *
  97      * @see ScriptAndLanguageTags.h for language codes.
  98      *
  99      * @internal
 100      */
 101     le_int32 fLanguageCode;
 102
 103     /**
 104      * The typographic control flags
 105      *
 106      * @internal
 107      */
 108     le_int32 fTypoFlags;
 109
 110     /**
 111      * <code>TRUE</code> if <code>mapCharsToGlyphs</code> should replace ZWJ / ZWNJ with a glyph
 112      * with no contours.
 113      *
 114      * @internal
 115      */
 116     le_bool fFilterZeroWidth;
 117
 118     /**
 119      * This constructs an instance for a given font, script and language. Subclass constructors
 120      * must call this constructor.
 121      *
 122      * @param fontInstance - the font for the text
 123      * @param scriptCode - the script for the text
 124      * @param languageCode - the language for the text
 125      * @param typoFlags - the typographic control flags for the text.  Set bit 1 if kerning
 126      * is desired, set bit 2 if ligature formation is desired.  Others are reserved.
 127      *
 128      * @see LEFontInstance
 129      * @see ScriptAndLanguageTags.h
 130      *
 131      * @internal
 132      */
 133     LayoutEngine(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typoFlags);
 134
 135     /**
 136      * This overrides the default no argument constructor to make it
 137      * difficult for clients to call it. Clients are expected to call
 138      * layoutEngineFactory.
 139      *
 140      * @internal
 141      */
 142     LayoutEngine();
 143
 144     /**
 145      * This method does any required pre-processing to the input characters. It
 146      * may generate output characters that differ from the input charcters due to
 147      * insertions, deletions, or reorderings. In such cases, it will also generate an
 148      * output character index array reflecting these changes.
 149      *
 150      * Subclasses must override this method.
 151      *
 152      * Input parameters:
 153      * @param chars - the input character context
 154      * @param offset - the index of the first character to process
 155      * @param count - the number of characters to process
 156      * @param max - the number of characters in the input context
 157      * @param rightToLeft - TRUE if the characters are in a right to left directional run
 158      * @param outChars - the output character array, if different from the input
 159      * @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
 160      * @param success - set to an error code if the operation fails
 161      *
 162      * @return the output character count (input character count if no change)
 163      *
 164      * @internal
 165      */
 166     virtual le_int32 characterProcessing(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft,
 167             LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 168
 169     /**
 170      * This method does the glyph processing. It converts an array of characters
 171      * into an array of glyph indices and character indices. The characters to be
 172      * processed are passed in a surrounding context. The context is specified as
 173      * a starting address and a maximum character count. An offset and a count are
 174      * used to specify the characters to be processed.
 175      *
 176      * The default implementation of this method only does character to glyph mapping.
 177      * Subclasses needing more elaborate glyph processing must override this method.
 178      *
 179      * Input parameters:
 180      * @param chars - the character context
 181      * @param offset - the offset of the first character to process
 182      * @param count - the number of characters to process
 183      * @param max - the number of characters in the context.
 184      * @param rightToLeft - TRUE if the text is in a right to left directional run
 185      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
 186      *                       will be set.
 187      *
 188      * Output parameters:
 189      * @param success - set to an error code if the operation fails
 190      *
 191      * @return the number of glyphs in the glyph index array
 192      *
 193      * @internal
 194      */
 195     virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 196
 197     /**
 198      * This method does basic glyph positioning. The default implementation positions
 199      * the glyphs based on their advance widths. This is sufficient for most uses. It
 200      * is not expected that many subclasses will override this method.
 201      *
 202      * Input parameters:
 203      * @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
 204      * @param x - the starting X position
 205      * @param y - the starting Y position
 206      * @param success - set to an error code if the operation fails
 207      *
 208      * @internal
 209      */
 210     virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
 211
 212     /**
 213      * This method does positioning adjustments like accent positioning and
 214      * kerning. The default implementation does nothing. Subclasses needing
 215      * position adjustments must override this method.
 216      *
 217      * Note that this method has both characters and glyphs as input so that
 218      * it can use the character codes to determine glyph types if that information
 219      * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
 220      * table)
 221      *
 222      * @param chars - the input character context
 223      * @param offset - the offset of the first character to process
 224      * @param count - the number of characters to process
 225      * @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
 226      * @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
 227      *                       adjusted as needed.
 228      * @param success - output parameter set to an error code if the operation fails
 229      *
 230      * @internal
 231      */
 232     virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 233
 234     /**
 235      * This method gets a table from the font associated with
 236      * the text. The default implementation gets the table from
 237      * the font instance. Subclasses which need to get the tables
 238      * some other way must override this method.
 239      *
 240      * @param tableTag - the four byte table tag.
 241      *
 242      * @return the address of the table.
 243      *
 244      * @internal
 245      */
 246     virtual const void *getFontTable(LETag tableTag) const;
 247
 248     /**
 249      * This method does character to glyph mapping. The default implementation
 250      * uses the font instance to do the mapping. It will allocate the glyph and
 251      * character index arrays if they're not already allocated. If it allocates the
 252      * character index array, it will fill it it.
 253      *
 254      * This method supports right to left
 255      * text with the ability to store the glyphs in reverse order, and by supporting
 256      * character mirroring, which will replace a character which has a left and right
 257      * form, such as parens, with the opposite form before mapping it to a glyph index.
 258      *
 259      * Input parameters:
 260      * @param chars - the input character context
 261      * @param offset - the offset of the first character to be mapped
 262      * @param count - the number of characters to be mapped
 263      * @param reverse - if <code>TRUE</code>, the output will be in reverse order
 264      * @param mirror - if <code>TRUE</code>, do character mirroring
 265      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
 266      *                       indices arrays will be filled in.
 267      * @param success - set to an error code if the operation fails
 268      *
 269      * @see LEFontInstance
 270      *
 271      * @internal
 272      */
 273     virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 274
 275     /**
 276      * This is a convenience method that forces the advance width of mark
 277      * glyphs to be zero, which is required for proper selection and highlighting.
 278      *
 279      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 280      * @param markFilter - used to identify mark glyphs
 281      * @param success - output parameter set to an error code if the operation fails
 282      *
 283      * @see LEGlyphFilter
 284      *
 285      * @internal
 286      */
 287     static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 288
 289
 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      * This method uses the input characters to identify marks. This is required in
 294      * cases where the font does not contain enough information to identify them based
 295      * on the glyph IDs.
 296      *
 297      * @param chars - the array of input characters
 298      * @param charCount - the number of input characers
 299      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 300      * @param reverse - <code>TRUE</code> if the glyph array has been reordered
 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(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 309
 310
 311 public:
 312     /**
 313      * The destructor. It will free any storage allocated for the
 314      * glyph, character index and position arrays by calling the reset
 315      * method. It is declared virtual so that it will be invoked by the
 316      * subclass destructors.
 317      *
 318      * @stable ICU 2.8
 319      */
 320     virtual ~LayoutEngine();
 321
 322     /**
 323      * This method will invoke the layout steps in their correct order by calling
 324      * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
 325      * compute the glyph, character index and position arrays.
 326      *
 327      * @param chars - the input character context
 328      * @param offset - the offset of the first character to process
 329      * @param count - the number of characters to process
 330      * @param max - the number of characters in the input context
 331      * @param rightToLeft - TRUE if the characers are in a right to left directional run
 332      * @param x - the initial X position
 333      * @param y - the initial Y position
 334      * @param success - output parameter set to an error code if the operation fails
 335      *
 336      * @return the number of glyphs in the glyph array
 337      *
 338      * Note: The glyph, character index and position array can be accessed
 339      * using the getter methods below.
 340      *
 341      * Note: If you call this method more than once, you must call the reset()
 342      * method first to free the glyph, character index and position arrays
 343      * allocated by the previous call.
 344      *
 345      * @stable ICU 2.8
 346      */
 347     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);
 348
 349     /**
 350      * This method returns the number of glyphs in the glyph array. Note
 351      * that the number of glyphs will be greater than or equal to the number
 352      * of characters used to create the LayoutEngine.
 353      *
 354      * @return the number of glyphs in the glyph array
 355      *
 356      * @stable ICU 2.8
 357      */
 358     le_int32 getGlyphCount() const;
 359
 360     /**
 361      * This method copies the glyph array into a caller supplied array.
 362      * The caller must ensure that the array is large enough to hold all
 363      * the glyphs.
 364      *
 365      * @param glyphs - the destiniation glyph array
 366      * @param success - set to an error code if the operation fails
 367      *
 368      * @stable ICU 2.8
 369      */
 370     void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
 371
 372     /**
 373      * This method copies the glyph array into a caller supplied array,
 374      * ORing in extra bits. (This functionality is needed by the JDK,
 375      * which uses 32 bits pre glyph idex, with the high 16 bits encoding
 376      * the composite font slot number)
 377      *
 378      * @param glyphs - the destination (32 bit) glyph array
 379      * @param extraBits - this value will be ORed with each glyph index
 380      * @param success - set to an error code if the operation fails
 381      *
 382      * @stable ICU 2.8
 383      */
 384     virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
 385
 386     /**
 387      * This method copies the character index array into a caller supplied array.
 388      * The caller must ensure that the array is large enough to hold a
 389      * character index for each glyph.
 390      *
 391      * @param charIndices - the destiniation character index array
 392      * @param success - set to an error code if the operation fails
 393      *
 394      * @stable ICU 2.8
 395      */
 396     void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
 397
 398     /**
 399      * This method copies the character index array into a caller supplied array.
 400      * The caller must ensure that the array is large enough to hold a
 401      * character index for each glyph.
 402      *
 403      * @param charIndices - the destiniation character index array
 404      * @param indexBase - an offset which will be added to each index
 405      * @param success - set to an error code if the operation fails
 406      *
 407      * @stable ICU 2.8
 408      */
 409     void getCharIndices(le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const;
 410
 411     /**
 412      * This method copies the position array into a caller supplied array.
 413      * The caller must ensure that the array is large enough to hold an
 414      * X and Y position for each glyph, plus an extra X and Y for the
 415      * advance of the last glyph.
 416      *
 417      * @param positions - the destiniation position array
 418      * @param success - set to an error code if the operation fails
 419      *
 420      * @stable ICU 2.8
 421      */
 422     void getGlyphPositions(float positions[], LEErrorCode &success) const;
 423
 424     /**
 425      * This method returns the X and Y position of the glyph at
 426      * the given index.
 427      *
 428      * Input parameters:
 429      * @param glyphIndex - the index of the glyph
 430      *
 431      * Output parameters:
 432      * @param x - the glyph's X position
 433      * @param y - the glyph's Y position
 434      * @param success - set to an error code if the operation fails
 435      *
 436      * @stable ICU 2.8
 437      */
 438     void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
 439
 440     /**
 441      * This method frees the glyph, character index and position arrays
 442      * so that the LayoutEngine can be reused to layout a different
 443      * characer array. (This method is also called by the destructor)
 444      *
 445      * @stable ICU 2.8
 446      */
 447     virtual void reset();
 448
 449     /**
 450      * This method returns a LayoutEngine capable of laying out text
 451      * in the given font, script and langauge. Note that the LayoutEngine
 452      * returned may be a subclass of LayoutEngine.
 453      *
 454      * @param fontInstance - the font of the text
 455      * @param scriptCode - the script of the text
 456      * @param languageCode - the language of the text
 457      * @param success - output parameter set to an error code if the operation fails
 458      *
 459      * @return a LayoutEngine which can layout text in the given font.
 460      *
 461      * @see LEFontInstance
 462      *
 463      * @stable ICU 2.8
 464      */
 465     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
 466
 467     /**
 468      * Override of existing call that provides flags to control typography.
 469      * @stable ICU 3.4
 470      */
 471     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
 472
 473     /**
 474      * ICU "poor man's RTTI", returns a UClassID for the actual class.
 475      *
 476      * @stable ICU 2.8
 477      */
 478     virtual UClassID getDynamicClassID() const;
 479
 480     /**
 481      * ICU "poor man's RTTI", returns a UClassID for this class.
 482      *
 483      * @stable ICU 2.8
 484      */
 485     static UClassID getStaticClassID();
 486
 487 };
 488
 489 U_NAMESPACE_END
 490 #endif
 491