1 /*
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3  *
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8  * by Oracle in the LICENSE file that accompanied this code.
9  *
10  * This code is distributed in the hope that it will be useful, but WITHOUT
11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13  * version 2 for more details (a copy is included in the LICENSE file that
14  * accompanied this code).
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25 
26 /*
27  *
28  * (C) Copyright IBM Corp. 2003 - All Rights Reserved
29  */
30 
31 package sun.font;
32 
33 /**
34  * Iterates over runs of fonts in a CompositeFont, optionally taking script runs into account.
35  */
36 public final class FontRunIterator {
37     CompositeFont font;
38     char[] text;
39     int start;
40     int limit;
41 
42     CompositeGlyphMapper mapper; // handy cache
43 
44     int slot = -1;
45     int pos;
46 
init(CompositeFont font, char[] text, int start, int limit)47     public void init(CompositeFont font, char[] text, int start, int limit) {
48         if (font == null || text == null || start < 0 || limit < start || limit > text.length) {
49             throw new IllegalArgumentException();
50         }
51 
52         this.font = font;
53         this.text = text;
54         this.start = start;
55         this.limit = limit;
56 
57         this.mapper = (CompositeGlyphMapper)font.getMapper();
58         this.slot = -1;
59         this.pos = start;
60     }
61 
getFont()62     public PhysicalFont getFont() {
63         return slot == -1 ? null : font.getSlotFont(slot);
64     }
65 
getGlyphMask()66     public int getGlyphMask() {
67         return slot << 24;
68     }
69 
getPos()70     public int getPos() {
71         return pos;
72     }
73 
74     /*
75      * characters that are in the 'common' script become part of the
76      * surrounding script run.  we want to fetch these from the same font
77      * used to get surrounding characters, where possible.  but we don't
78      * want to force non-common characters to come from other than their
79      * standard font.
80      *
81      * what we really want to do is this:
82      * 1) fetch a code point from the text.
83      * 2) get its 'native' script code
84      * 3) determine its 'resolved' script code
85      * 4) if its native script is COMMON, and its resolved script is the same as the previous
86      *    code point's, then see if the previous font supports this code point.  if so, use it.
87      * 5) otherwise resolve the font as usual
88      * 6) break the run when either the physical font or the resolved script changes.
89      *
90      * problems: we optimize latin-1 and cjk text assuming a fixed
91      * width for each character.  since latin-1 digits and punctuation
92      * are common, following this algorithm they will change to match
93      * the fonts used for the preceding text, and potentially change metrics.
94      *
95      * this also seems to have the potential for changing arbitrary runs of text, e.g.
96      * any number of digits and spaces can change depending on the preceding (or following!)
97      * non-COMMON character's font assignment.  this is not good.
98      *
99      * since the goal is to enable layout to be performed using as few physical fonts as
100      * possible, and the primary cause of switching fonts is to handle spaces, perhaps
101      * we should just special-case spaces and assign them from the current font, whatever
102      * it may be.
103      *
104      * One could also argue that the job of the composite font is to assign physical fonts
105      * to text runs, however it wishes.  we don't necessarily have to provide script info
106      * to let it do this.  it can determine based on whatever.  so having a special 'next'
107      * function that takes script (and limit) is redundant.  It can fetch the script again
108      * if need be.
109      *
110      * both this and the script iterator are turning char sequences into code point
111      * sequences.  maybe it would be better to feed a single code point into each iterator-- push
112      * the data instead of pull it?
113      */
114 
next(int script, int lim)115     public boolean next(int script, int lim) {
116         if (pos == lim) {
117             return false;
118         }
119 
120         int ch = nextCodePoint(lim);
121         int sl = mapper.charToGlyph(ch) & CompositeGlyphMapper.SLOTMASK;
122         slot = sl >>> 24;
123         while ((ch = nextCodePoint(lim)) != DONE && (mapper.charToGlyph(ch) & CompositeGlyphMapper.SLOTMASK) == sl);
124         pushback(ch);
125 
126         return true;
127     }
128 
next()129     public boolean next() {
130         return next(Script.COMMON, limit);
131     }
132 
133     static final int SURROGATE_START = 0x10000;
134     static final int LEAD_START = 0xd800;
135     static final int LEAD_LIMIT = 0xdc00;
136     static final int TAIL_START = 0xdc00;
137     static final int TAIL_LIMIT = 0xe000;
138     static final int LEAD_SURROGATE_SHIFT = 10;
139     static final int SURROGATE_OFFSET = SURROGATE_START - (LEAD_START << LEAD_SURROGATE_SHIFT) - TAIL_START;
140 
141     static final int DONE = -1;
142 
nextCodePoint()143     int nextCodePoint() {
144         return nextCodePoint(limit);
145     }
146 
nextCodePoint(int lim)147     int nextCodePoint(int lim) {
148         if (pos >= lim) {
149             return DONE;
150         }
151         int ch = text[pos++];
152         if (ch >= LEAD_START && ch < LEAD_LIMIT && pos < lim) {
153             int nch = text[pos];
154             if (nch >= TAIL_START && nch < TAIL_LIMIT) {
155                 ++pos;
156                 ch = (ch << LEAD_SURROGATE_SHIFT) + nch + SURROGATE_OFFSET;
157             }
158         }
159         return ch;
160     }
161 
pushback(int ch)162     void pushback(int ch) {
163         if (ch >= 0) {
164             if (ch >= 0x10000) {
165                 pos -= 2;
166             } else {
167                 pos -= 1;
168             }
169         }
170     }
171 }
172