LEFontInstance.h revision 51cfa1a9a96cad34675a6415fe86dfdf3f525bb6 
1
2/*
3 *
4 * (C) Copyright IBM Corp. 1998-2007 - All Rights Reserved
5 *
6 */
7
8#ifndef __LEFONTINSTANCE_H
9#define __LEFONTINSTANCE_H
10
11#include "LETypes.h"
12/**
13 * \file
14 * \brief C++ API: Layout Engine Font Instance object
15 */
16
17U_NAMESPACE_BEGIN
18
19/**
20 * Instances of this class are used by <code>LEFontInstance::mapCharsToGlyphs</code> and
21 * <code>LEFontInstance::mapCharToGlyph</code> to adjust character codes before the character
22 * to glyph mapping process. Examples of this are filtering out control characters
23 * and character mirroring - replacing a character which has both a left and a right
24 * hand form with the opposite form.
25 *
26 * @stable ICU 3.2
27 */
28class LECharMapper /* not : public UObject because this is an interface/mixin class */
29{
30public:
31    /**
32     * Destructor.
33     * @stable ICU 3.2
34     */
35    virtual ~LECharMapper();
36
37    /**
38     * This method does the adjustments.
39     *
40     * @param ch - the input character
41     *
42     * @return the adjusted character
43     *
44     * @stable ICU 2.8
45     */
46    virtual LEUnicode32 mapChar(LEUnicode32 ch) const = 0;
47};
48
49/**
50 * This is a forward reference to the class which holds the per-glyph
51 * storage.
52 *
53 * @stable ICU 3.0
54 */
55class LEGlyphStorage;
56
57/**
58 * This is a virtual base class that serves as the interface between a LayoutEngine
59 * and the platform font environment. It allows a LayoutEngine to access font tables, do
60 * character to glyph mapping, and obtain metrics information without knowing any platform
61 * specific details. There are also a few utility methods for converting between points,
62 * pixels and funits. (font design units)
63 *
64 * An instance of an <code>LEFontInstance</code> represents a font at a particular point
65 * size. Each instance can represent either a single physical font, or a composite font.
66 * A composite font is a collection of physical fonts, each of which contains a subset of
67 * the characters contained in the composite font.
68 *
69 * Note: with the exception of <code>getSubFont</code>, the methods in this class only
70 * make sense for a physical font. If you have an <code>LEFontInstance</code> which
71 * represents a composite font you should only call the methods below which have
72 * an <code>LEGlyphID</code>, an <code>LEUnicode</code> or an <code>LEUnicode32</code>
73 * as one of the arguments because these can be used to select a particular subfont.
74 *
75 * Subclasses which implement composite fonts should supply an implementation of these
76 * methods with some default behavior such as returning constant values, or using the
77 * values from the first subfont.
78 *
79 * @stable ICU 3.0
80 */
81class U_LAYOUT_API LEFontInstance : public UObject
82{
83public:
84
85    /**
86     * This virtual destructor is here so that the subclass
87     * destructors can be invoked through the base class.
88     *
89     * @stable ICU 2.8
90     */
91    virtual ~LEFontInstance();
92
93    /**
94     * Get a physical font which can render the given text. For composite fonts,
95     * if there is no single physical font which can render all of the text,
96     * return a physical font which can render an initial substring of the text,
97     * and set the <code>offset</code> parameter to the end of that substring.
98     *
99     * Internally, the LayoutEngine works with runs of text all in the same
100     * font and script, so it is best to call this method with text which is
101     * in a single script, passing the script code in as a hint. If you don't
102     * know the script of the text, you can use zero, which is the script code
103     * for characters used in more than one script.
104     *
105     * The default implementation of this method is intended for instances of
106     * <code>LEFontInstance</code> which represent a physical font. It returns
107     * <code>this</code> and indicates that the entire string can be rendered.
108     *
109     * This method will return a valid <code>LEFontInstance</code> unless you
110     * have passed illegal parameters, or an internal error has been encountered.
111     * For composite fonts, it may return the warning <code>LE_NO_SUBFONT_WARNING</code>
112     * to indicate that the returned font may not be able to render all of
113     * the text. Whenever a valid font is returned, the <code>offset</code> parameter
114     * will be advanced by at least one.
115     *
116     * Subclasses which implement composite fonts must override this method.
117     * Where it makes sense, they should use the script code as a hint to render
118     * characters from the COMMON script in the font which is used for the given
119     * script. For example, if the input text is a series of Arabic words separated
120     * by spaces, and the script code passed in is <code>arabScriptCode</code> you
121     * should return the font used for Arabic characters for all of the input text,
122     * including the spaces. If, on the other hand, the input text contains characters
123     * which cannot be rendered by the font used for Arabic characters, but which can
124     * be rendered by another font, you should return that font for those characters.
125     *
126     * @param chars   - the array of Unicode characters.
127     * @param offset  - a pointer to the starting offset in the text. On exit this
128     *                  will be set the the limit offset of the text which can be
129     *                  rendered using the returned font.
130     * @param limit   - the limit offset for the input text.
131     * @param script  - the script hint.
132     * @param success - set to an error code if the arguments are illegal, or no font
133     *                  can be returned for some reason. May also be set to
134     *                  <code>LE_NO_SUBFONT_WARNING</code> if the subfont which
135     *                  was returned cannot render all of the text.
136     *
137     * @return an <code>LEFontInstance</code> for the sub font which can render the characters, or
138     *         <code>NULL</code> if there is an error.
139     *
140     * @see LEScripts.h
141     *
142     * @stable ICU 3.2
143     */
144    virtual const LEFontInstance *getSubFont(const LEUnicode chars[], le_int32 *offset, le_int32 limit, le_int32 script, LEErrorCode &success) const;
145
146    //
147    // Font file access
148    //
149
150    /**
151     * This method reads a table from the font. Note that in general,
152     * it only makes sense to call this method on an <code>LEFontInstance</code>
153     * which represents a physical font - i.e. one which has been returned by
154     * <code>getSubFont()</code>. This is because each subfont in a composite font
155     * will have different tables, and there's no way to know which subfont to access.
156     *
157     * Subclasses which represent composite fonts should always return <code>NULL</code>.
158     *
159     * @param tableTag - the four byte table tag. (e.g. 'cmap')
160     *
161     * @return the address of the table in memory, or <code>NULL</code>
162     *         if the table doesn't exist.
163     *
164     * @stable ICU 2.8
165     */
166    virtual const void *getFontTable(LETag tableTag) const = 0;
167
168    /**
169     * This method is used to determine if the font can
170     * render the given character. This can usually be done
171     * by looking the character up in the font's character
172     * to glyph mapping.
173     *
174     * The default implementation of this method will return
175     * <code>TRUE</code> if <code>mapCharToGlyph(ch)</code>
176     * returns a non-zero value.
177     *
178     * @param ch - the character to be tested
179     *
180     * @return <code>TRUE</code> if the font can render ch.
181     *
182     * @stable ICU 3.2
183     */
184    virtual le_bool canDisplay(LEUnicode32 ch) const;
185
186    /**
187     * This method returns the number of design units in
188     * the font's EM square.
189     *
190     * @return the number of design units pre EM.
191     *
192     * @stable ICU 2.8
193     */
194    virtual le_int32 getUnitsPerEM() const = 0;
195
196    /**
197     * This method maps an array of character codes to an array of glyph
198     * indices, using the font's character to glyph map.
199     *
200     * The default implementation iterates over all of the characters and calls
201     * <code>mapCharToGlyph(ch, mapper)</code> on each one. It also handles surrogate
202     * characters, storing the glyph ID for the high surrogate, and a deleted glyph (0xFFFF)
203     * for the low surrogate.
204     *
205     * Most sublcasses will not need to implement this method.
206     *
207     * @param chars - the character array
208     * @param offset - the index of the first character
209     * @param count - the number of characters
210     * @param reverse - if <code>TRUE</code>, store the glyph indices in reverse order.
211     * @param mapper - the character mapper.
212     * @param filterZeroWidth - <code>TRUE</code> if ZWJ / ZWNJ characters should map to a glyph w/ no contours.
213     * @param glyphStorage - the object which contains the output glyph array
214     *
215     * @see LECharMapper
216     *
217     * @stable ICU 3.6
218     */
219    virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, const LECharMapper *mapper, le_bool filterZeroWidth, LEGlyphStorage &glyphStorage) const;
220
221    /**
222     * This method maps a single character to a glyph index, using the
223     * font's character to glyph map. The default implementation of this
224     * method calls the mapper, and then calls <code>mapCharToGlyph(mappedCh)</code>.
225     *
226     * @param ch - the character
227     * @param mapper - the character mapper
228     * @param filterZeroWidth - <code>TRUE</code> if ZWJ / ZWNJ characters should map to a glyph w/ no contours.
229     *
230     * @return the glyph index
231     *
232     * @see LECharMapper
233     *
234     * @stable ICU 3.6
235     */
236    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const;
237
238    /**
239     * This method maps a single character to a glyph index, using the
240     * font's character to glyph map. The default implementation of this
241     * method calls the mapper, and then calls <code>mapCharToGlyph(mappedCh)</code>.
242     *
243     * @param ch - the character
244     * @param mapper - the character mapper
245     *
246     * @return the glyph index
247     *
248     * @see LECharMapper
249     *
250     * @stable ICU 3.2
251     */
252    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const;
253
254    /**
255     * This method maps a single character to a glyph index, using the
256     * font's character to glyph map. There is no default implementation
257     * of this method because it requires information about the platform
258     * font implementation.
259     *
260     * @param ch - the character
261     *
262     * @return the glyph index
263     *
264     * @stable ICU 3.2
265     */
266    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch) const = 0;
267
268    //
269    // Metrics
270    //
271
272    /**
273     * This method gets the X and Y advance of a particular glyph, in pixels.
274     *
275     * @param glyph - the glyph index
276     * @param advance - the X and Y pixel values will be stored here
277     *
278     * @stable ICU 3.2
279     */
280    virtual void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const = 0;
281
282    /**
283     * This method gets the hinted X and Y pixel coordinates of a particular
284     * point in the outline of the given glyph.
285     *
286     * @param glyph - the glyph index
287     * @param pointNumber - the number of the point
288     * @param point - the point's X and Y pixel values will be stored here
289     *
290     * @return <code>TRUE</code> if the point coordinates could be stored.
291     *
292     * @stable ICU 2.8
293     */
294    virtual le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const = 0;
295
296    /**
297     * This method returns the width of the font's EM square
298     * in pixels.
299     *
300     * @return the pixel width of the EM square
301     *
302     * @stable ICU 2.8
303     */
304    virtual float getXPixelsPerEm() const = 0;
305
306    /**
307     * This method returns the height of the font's EM square
308     * in pixels.
309     *
310     * @return the pixel height of the EM square
311     *
312     * @stable ICU 2.8
313     */
314    virtual float getYPixelsPerEm() const = 0;
315
316    /**
317     * This method converts font design units in the
318     * X direction to points.
319     *
320     * @param xUnits - design units in the X direction
321     *
322     * @return points in the X direction
323     *
324     * @stable ICU 3.2
325     */
326    virtual float xUnitsToPoints(float xUnits) const;
327
328    /**
329     * This method converts font design units in the
330     * Y direction to points.
331     *
332     * @param yUnits - design units in the Y direction
333     *
334     * @return points in the Y direction
335     *
336     * @stable ICU 3.2
337     */
338    virtual float yUnitsToPoints(float yUnits) const;
339
340    /**
341     * This method converts font design units to points.
342     *
343     * @param units - X and Y design units
344     * @param points - set to X and Y points
345     *
346     * @stable ICU 3.2
347     */
348    virtual void unitsToPoints(LEPoint &units, LEPoint &points) const;
349
350    /**
351     * This method converts pixels in the
352     * X direction to font design units.
353     *
354     * @param xPixels - pixels in the X direction
355     *
356     * @return font design units in the X direction
357     *
358     * @stable ICU 3.2
359     */
360    virtual float xPixelsToUnits(float xPixels) const;
361
362    /**
363     * This method converts pixels in the
364     * Y direction to font design units.
365     *
366     * @param yPixels - pixels in the Y direction
367     *
368     * @return font design units in the Y direction
369     *
370     * @stable ICU 3.2
371     */
372    virtual float yPixelsToUnits(float yPixels) const;
373
374    /**
375     * This method converts pixels to font design units.
376     *
377     * @param pixels - X and Y pixel
378     * @param units - set to X and Y font design units
379     *
380     * @stable ICU 3.2
381     */
382    virtual void pixelsToUnits(LEPoint &pixels, LEPoint &units) const;
383
384    /**
385     * Get the X scale factor from the font's transform. The default
386     * implementation of <code>transformFunits()</code> will call this method.
387     *
388     * @return the X scale factor.
389     *
390     *
391     * @see transformFunits
392     *
393     * @stable ICU 3.2
394     */
395    virtual float getScaleFactorX() const = 0;
396
397    /**
398     * Get the Y scale factor from the font's transform. The default
399     * implementation of <code>transformFunits()</code> will call this method.
400     *
401     * @return the Yscale factor.
402     *
403     * @see transformFunits
404     *
405     * @stable ICU 3.2
406     */
407    virtual float getScaleFactorY() const = 0;
408
409    /**
410     * This method transforms an X, Y point in font design units to a
411     * pixel coordinate, applying the font's transform. The default
412     * implementation of this method calls <code>getScaleFactorX()</code>
413     * and <code>getScaleFactorY()</code>.
414     *
415     * @param xFunits - the X coordinate in font design units
416     * @param yFunits - the Y coordinate in font design units
417     * @param pixels - the tranformed co-ordinate in pixels
418     *
419     * @see getScaleFactorX
420     * @see getScaleFactorY
421     *
422     * @stable ICU 3.2
423     */
424    virtual void transformFunits(float xFunits, float yFunits, LEPoint &pixels) const;
425
426    /**
427     * This is a convenience method used to convert
428     * values in a 16.16 fixed point format to floating point.
429     *
430     * @param fixed - the fixed point value
431     *
432     * @return the floating point value
433     *
434     * @stable ICU 2.8
435     */
436    static inline float fixedToFloat(le_int32 fixed);
437
438    /**
439     * This is a convenience method used to convert
440     * floating point values to 16.16 fixed point format.
441     *
442     * @param theFloat - the floating point value
443     *
444     * @return the fixed point value
445     *
446     * @stable ICU 2.8
447     */
448    static inline le_int32 floatToFixed(float theFloat);
449
450    //
451    // These methods won't ever be called by the LayoutEngine,
452    // but are useful for clients of <code>LEFontInstance</code> who
453    // need to render text.
454    //
455
456    /**
457     * Get the font's ascent.
458     *
459     * @return the font's ascent, in points. This value
460     * will always be positive.
461     *
462     * @stable ICU 3.2
463     */
464    virtual le_int32 getAscent() const = 0;
465
466    /**
467     * Get the font's descent.
468     *
469     * @return the font's descent, in points. This value
470     * will always be positive.
471     *
472     * @stable ICU 3.2
473     */
474    virtual le_int32 getDescent() const = 0;
475
476    /**
477     * Get the font's leading.
478     *
479     * @return the font's leading, in points. This value
480     * will always be positive.
481     *
482     * @stable ICU 3.2
483     */
484    virtual le_int32 getLeading() const = 0;
485
486    /**
487     * Get the line height required to display text in
488     * this font. The default implementation of this method
489     * returns the sum of the ascent, descent, and leading.
490     *
491     * @return the line height, in points. This vaule will
492     * always be positive.
493     *
494     * @stable ICU 3.2
495     */
496    virtual le_int32 getLineHeight() const;
497
498    /**
499     * ICU "poor man's RTTI", returns a UClassID for the actual class.
500     *
501     * @stable ICU 3.2
502     */
503    virtual UClassID getDynamicClassID() const;
504
505    /**
506     * ICU "poor man's RTTI", returns a UClassID for this class.
507     *
508     * @stable ICU 3.2
509     */
510    static UClassID getStaticClassID();
511
512};
513
514inline float LEFontInstance::fixedToFloat(le_int32 fixed)
515{
516    return (float) (fixed / 65536.0);
517}
518
519inline le_int32 LEFontInstance::floatToFixed(float theFloat)
520{
521    return (le_int32) (theFloat * 65536.0);
522}
523
524U_NAMESPACE_END
525#endif
526
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528