icuSources/layout/LayoutEngine.h

   1
   2 /*
   3  *
   4  * (C) Copyright IBM Corp. 1998-2008 - 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      * @param success - set to an error code if the operation fails
 128      *
 129      * @see LEFontInstance
 130      * @see ScriptAndLanguageTags.h
 131      *
 132      * @internal
 133      */
 134     LayoutEngine(const LEFontInstance *fontInstance,
 135                  le_int32 scriptCode,
 136                  le_int32 languageCode,
 137                  le_int32 typoFlags,
 138                  LEErrorCode &success);
 139
 140     /**
 141      * This overrides the default no argument constructor to make it
 142      * difficult for clients to call it. Clients are expected to call
 143      * layoutEngineFactory.
 144      *
 145      * @internal
 146      */
 147     LayoutEngine();
 148
 149     /**
 150      * This method does any required pre-processing to the input characters. It
 151      * may generate output characters that differ from the input charcters due to
 152      * insertions, deletions, or reorderings. In such cases, it will also generate an
 153      * output character index array reflecting these changes.
 154      *
 155      * Subclasses must override this method.
 156      *
 157      * Input parameters:
 158      * @param chars - the input character context
 159      * @param offset - the index of the first character to process
 160      * @param count - the number of characters to process
 161      * @param max - the number of characters in the input context
 162      * @param rightToLeft - TRUE if the characters are in a right to left directional run
 163      * @param outChars - the output character array, if different from the input
 164      * @param glyphStorage - the object that holds the per-glyph storage. The character index array may be set.
 165      * @param success - set to an error code if the operation fails
 166      *
 167      * @return the output character count (input character count if no change)
 168      *
 169      * @internal
 170      */
 171     virtual le_int32 characterProcessing(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft,
 172             LEUnicode *&outChars, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 173
 174     /**
 175      * This method does the glyph processing. It converts an array of characters
 176      * into an array of glyph indices and character indices. The characters to be
 177      * processed are passed in a surrounding context. The context is specified as
 178      * a starting address and a maximum character count. An offset and a count are
 179      * used to specify the characters to be processed.
 180      *
 181      * The default implementation of this method only does character to glyph mapping.
 182      * Subclasses needing more elaborate glyph processing must override this method.
 183      *
 184      * Input parameters:
 185      * @param chars - the character context
 186      * @param offset - the offset of the first character to process
 187      * @param count - the number of characters to process
 188      * @param max - the number of characters in the context.
 189      * @param rightToLeft - TRUE if the text is in a right to left directional run
 190      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char indices arrays
 191      *                       will be set.
 192      *
 193      * Output parameters:
 194      * @param success - set to an error code if the operation fails
 195      *
 196      * @return the number of glyphs in the glyph index array
 197      *
 198      * @internal
 199      */
 200     virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 201
 202     /**
 203      * This method does basic glyph positioning. The default implementation positions
 204      * the glyphs based on their advance widths. This is sufficient for most uses. It
 205      * is not expected that many subclasses will override this method.
 206      *
 207      * Input parameters:
 208      * @param glyphStorage - the object which holds the per-glyph storage. The glyph position array will be set.
 209      * @param x - the starting X position
 210      * @param y - the starting Y position
 211      * @param success - set to an error code if the operation fails
 212      *
 213      * @internal
 214      */
 215     virtual void positionGlyphs(LEGlyphStorage &glyphStorage, float x, float y, LEErrorCode &success);
 216
 217     /**
 218      * This method does positioning adjustments like accent positioning and
 219      * kerning. The default implementation does nothing. Subclasses needing
 220      * position adjustments must override this method.
 221      *
 222      * Note that this method has both characters and glyphs as input so that
 223      * it can use the character codes to determine glyph types if that information
 224      * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
 225      * table)
 226      *
 227      * @param chars - the input character context
 228      * @param offset - the offset of the first character to process
 229      * @param count - the number of characters to process
 230      * @param reverse - <code>TRUE</code> if the glyphs in the glyph array have been reordered
 231      * @param glyphStorage - the object which holds the per-glyph storage. The glyph positions will be
 232      *                       adjusted as needed.
 233      * @param success - output parameter set to an error code if the operation fails
 234      *
 235      * @internal
 236      */
 237     virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 238
 239     /**
 240      * This method gets a table from the font associated with
 241      * the text. The default implementation gets the table from
 242      * the font instance. Subclasses which need to get the tables
 243      * some other way must override this method.
 244      *
 245      * @param tableTag - the four byte table tag.
 246      *
 247      * @return the address of the table.
 248      *
 249      * @internal
 250      */
 251     virtual const void *getFontTable(LETag tableTag) const;
 252
 253     /**
 254      * This method does character to glyph mapping. The default implementation
 255      * uses the font instance to do the mapping. It will allocate the glyph and
 256      * character index arrays if they're not already allocated. If it allocates the
 257      * character index array, it will fill it it.
 258      *
 259      * This method supports right to left
 260      * text with the ability to store the glyphs in reverse order, and by supporting
 261      * character mirroring, which will replace a character which has a left and right
 262      * form, such as parens, with the opposite form before mapping it to a glyph index.
 263      *
 264      * Input parameters:
 265      * @param chars - the input character context
 266      * @param offset - the offset of the first character to be mapped
 267      * @param count - the number of characters to be mapped
 268      * @param reverse - if <code>TRUE</code>, the output will be in reverse order
 269      * @param mirror - if <code>TRUE</code>, do character mirroring
 270      * @param glyphStorage - the object which holds the per-glyph storage. The glyph and char
 271      *                       indices arrays will be filled in.
 272      * @param success - set to an error code if the operation fails
 273      *
 274      * @see LEFontInstance
 275      *
 276      * @internal
 277      */
 278     virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphStorage &glyphStorage, LEErrorCode &success);
 279
 280     /**
 281      * This is a convenience method that forces the advance width of mark
 282      * glyphs to be zero, which is required for proper selection and highlighting.
 283      *
 284      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 285      * @param markFilter - used to identify mark glyphs
 286      * @param success - output parameter set to an error code if the operation fails
 287      *
 288      * @see LEGlyphFilter
 289      *
 290      * @internal
 291      */
 292     static void adjustMarkGlyphs(LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 293
 294
 295     /**
 296      * This is a convenience method that forces the advance width of mark
 297      * glyphs to be zero, which is required for proper selection and highlighting.
 298      * This method uses the input characters to identify marks. This is required in
 299      * cases where the font does not contain enough information to identify them based
 300      * on the glyph IDs.
 301      *
 302      * @param chars - the array of input characters
 303      * @param charCount - the number of input characers
 304      * @param glyphStorage - the object containing the per-glyph storage. The positions array will be modified.
 305      * @param reverse - <code>TRUE</code> if the glyph array has been reordered
 306      * @param markFilter - used to identify mark glyphs
 307      * @param success - output parameter set to an error code if the operation fails
 308      *
 309      * @see LEGlyphFilter
 310      *
 311      * @internal
 312      */
 313     static void adjustMarkGlyphs(const LEUnicode chars[], le_int32 charCount, le_bool reverse, LEGlyphStorage &glyphStorage, LEGlyphFilter *markFilter, LEErrorCode &success);
 314
 315
 316 public:
 317     /**
 318      * The destructor. It will free any storage allocated for the
 319      * glyph, character index and position arrays by calling the reset
 320      * method. It is declared virtual so that it will be invoked by the
 321      * subclass destructors.
 322      *
 323      * @stable ICU 2.8
 324      */
 325     virtual ~LayoutEngine();
 326
 327     /**
 328      * This method will invoke the layout steps in their correct order by calling
 329      * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods. It will
 330      * compute the glyph, character index and position arrays.
 331      *
 332      * @param chars - the input character context
 333      * @param offset - the offset of the first character to process
 334      * @param count - the number of characters to process
 335      * @param max - the number of characters in the input context
 336      * @param rightToLeft - TRUE if the characers are in a right to left directional run
 337      * @param x - the initial X position
 338      * @param y - the initial Y position
 339      * @param success - output parameter set to an error code if the operation fails
 340      *
 341      * @return the number of glyphs in the glyph array
 342      *
 343      * Note: The glyph, character index and position array can be accessed
 344      * using the getter methods below.
 345      *
 346      * Note: If you call this method more than once, you must call the reset()
 347      * method first to free the glyph, character index and position arrays
 348      * allocated by the previous call.
 349      *
 350      * @stable ICU 2.8
 351      */
 352     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);
 353
 354     /**
 355      * This method returns the number of glyphs in the glyph array. Note
 356      * that the number of glyphs will be greater than or equal to the number
 357      * of characters used to create the LayoutEngine.
 358      *
 359      * @return the number of glyphs in the glyph array
 360      *
 361      * @stable ICU 2.8
 362      */
 363     le_int32 getGlyphCount() const;
 364
 365     /**
 366      * This method copies the glyph array into a caller supplied array.
 367      * The caller must ensure that the array is large enough to hold all
 368      * the glyphs.
 369      *
 370      * @param glyphs - the destiniation glyph array
 371      * @param success - set to an error code if the operation fails
 372      *
 373      * @stable ICU 2.8
 374      */
 375     void getGlyphs(LEGlyphID glyphs[], LEErrorCode &success) const;
 376
 377     /**
 378      * This method copies the glyph array into a caller supplied array,
 379      * ORing in extra bits. (This functionality is needed by the JDK,
 380      * which uses 32 bits pre glyph idex, with the high 16 bits encoding
 381      * the composite font slot number)
 382      *
 383      * @param glyphs - the destination (32 bit) glyph array
 384      * @param extraBits - this value will be ORed with each glyph index
 385      * @param success - set to an error code if the operation fails
 386      *
 387      * @stable ICU 2.8
 388      */
 389     virtual void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits, LEErrorCode &success) const;
 390
 391     /**
 392      * This method copies the character index array into a caller supplied array.
 393      * The caller must ensure that the array is large enough to hold a
 394      * character index for each glyph.
 395      *
 396      * @param charIndices - the destiniation character index array
 397      * @param success - set to an error code if the operation fails
 398      *
 399      * @stable ICU 2.8
 400      */
 401     void getCharIndices(le_int32 charIndices[], LEErrorCode &success) const;
 402
 403     /**
 404      * This method copies the character index array into a caller supplied array.
 405      * The caller must ensure that the array is large enough to hold a
 406      * character index for each glyph.
 407      *
 408      * @param charIndices - the destiniation character index array
 409      * @param indexBase - an offset which will be added to each index
 410      * @param success - set to an error code if the operation fails
 411      *
 412      * @stable ICU 2.8
 413      */
 414     void getCharIndices(le_int32 charIndices[], le_int32 indexBase, LEErrorCode &success) const;
 415
 416     /**
 417      * This method copies the position array into a caller supplied array.
 418      * The caller must ensure that the array is large enough to hold an
 419      * X and Y position for each glyph, plus an extra X and Y for the
 420      * advance of the last glyph.
 421      *
 422      * @param positions - the destiniation position array
 423      * @param success - set to an error code if the operation fails
 424      *
 425      * @stable ICU 2.8
 426      */
 427     void getGlyphPositions(float positions[], LEErrorCode &success) const;
 428
 429     /**
 430      * This method returns the X and Y position of the glyph at
 431      * the given index.
 432      *
 433      * Input parameters:
 434      * @param glyphIndex - the index of the glyph
 435      *
 436      * Output parameters:
 437      * @param x - the glyph's X position
 438      * @param y - the glyph's Y position
 439      * @param success - set to an error code if the operation fails
 440      *
 441      * @stable ICU 2.8
 442      */
 443     void getGlyphPosition(le_int32 glyphIndex, float &x, float &y, LEErrorCode &success) const;
 444
 445     /**
 446      * This method frees the glyph, character index and position arrays
 447      * so that the LayoutEngine can be reused to layout a different
 448      * characer array. (This method is also called by the destructor)
 449      *
 450      * @stable ICU 2.8
 451      */
 452     virtual void reset();
 453
 454     /**
 455      * This method returns a LayoutEngine capable of laying out text
 456      * in the given font, script and langauge. Note that the LayoutEngine
 457      * returned may be a subclass of LayoutEngine.
 458      *
 459      * @param fontInstance - the font of the text
 460      * @param scriptCode - the script of the text
 461      * @param languageCode - the language of the text
 462      * @param success - output parameter set to an error code if the operation fails
 463      *
 464      * @return a LayoutEngine which can layout text in the given font.
 465      *
 466      * @see LEFontInstance
 467      *
 468      * @stable ICU 2.8
 469      */
 470     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, LEErrorCode &success);
 471
 472     /**
 473      * Override of existing call that provides flags to control typography.
 474      * @stable ICU 3.4
 475      */
 476     static LayoutEngine *layoutEngineFactory(const LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode, le_int32 typo_flags, LEErrorCode &success);
 477
 478     /**
 479      * ICU "poor man's RTTI", returns a UClassID for the actual class.
 480      *
 481      * @stable ICU 2.8
 482      */
 483     virtual UClassID getDynamicClassID() const;
 484
 485     /**
 486      * ICU "poor man's RTTI", returns a UClassID for this class.
 487      *
 488      * @stable ICU 2.8
 489      */
 490     static UClassID getStaticClassID();
 491
 492 };
 493
 494 U_NAMESPACE_END
 495 #endif
 496