Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame^] | 1 | // Copyright 2011 Google Inc. All Rights Reserved. |
| 2 | |
| 3 | package android.text; |
| 4 | |
| 5 | |
| 6 | /** |
| 7 | * Some objects that implement TextDirectionHeuristic. |
| 8 | * @hide |
| 9 | */ |
| 10 | public class TextDirectionHeuristics { |
| 11 | |
| 12 | /** Always decides that the direction is left to right. */ |
| 13 | public static final TextDirectionHeuristic LTR = |
| 14 | new TextDirectionHeuristicInternal(null /* no algorithm */, false); |
| 15 | |
| 16 | /** Always decides that the direction is right to left. */ |
| 17 | public static final TextDirectionHeuristic RTL = |
| 18 | new TextDirectionHeuristicInternal(null /* no algorithm */, true); |
| 19 | |
| 20 | /** |
| 21 | * Determines the direction based on the first strong directional character, |
| 22 | * including bidi format chars, falling back to left to right if it |
| 23 | * finds none. This is the default behavior of the Unicode Bidirectional |
| 24 | * Algorithm. |
| 25 | */ |
| 26 | public static final TextDirectionHeuristic FIRSTSTRONG_LTR = |
| 27 | new TextDirectionHeuristicInternal(FirstStrong.INSTANCE, false); |
| 28 | |
| 29 | /** |
| 30 | * Determines the direction based on the first strong directional character, |
| 31 | * including bidi format chars, falling back to right to left if it |
| 32 | * finds none. This is similar to the default behavior of the Unicode |
| 33 | * Bidirectional Algorithm, just with different fallback behavior. |
| 34 | */ |
| 35 | public static final TextDirectionHeuristic FIRSTSTRONG_RTL = |
| 36 | new TextDirectionHeuristicInternal(FirstStrong.INSTANCE, true); |
| 37 | |
| 38 | /** |
| 39 | * If the text contains any strong right to left non-format character, determines |
| 40 | * that the direction is right to left, falling back to left to right if it |
| 41 | * finds none. |
| 42 | */ |
| 43 | public static final TextDirectionHeuristic ANYRTL_LTR = |
| 44 | new TextDirectionHeuristicInternal(AnyStrong.INSTANCE_RTL, false); |
| 45 | |
| 46 | /** |
| 47 | * If the text contains any strong left to right non-format character, determines |
| 48 | * that the direction is left to right, falling back to right to left if it |
| 49 | * finds none. |
| 50 | */ |
| 51 | public static final TextDirectionHeuristic ANYLTR_RTL = |
| 52 | new TextDirectionHeuristicInternal(AnyStrong.INSTANCE_LTR, true); |
| 53 | |
| 54 | /** |
| 55 | * Examines only the strong directional non-format characters, and if either |
| 56 | * left to right or right to left characters are 60% or more of this total, |
| 57 | * determines that the direction follows the majority of characters. Falls |
| 58 | * back to left to right if neither direction meets this threshold. |
| 59 | */ |
| 60 | public static final TextDirectionHeuristic CHARCOUNT_LTR = |
| 61 | new TextDirectionHeuristicInternal(CharCount.INSTANCE_DEFAULT, false); |
| 62 | |
| 63 | /** |
| 64 | * Examines only the strong directional non-format characters, and if either |
| 65 | * left to right or right to left characters are 60% or more of this total, |
| 66 | * determines that the direction follows the majority of characters. Falls |
| 67 | * back to right to left if neither direction meets this threshold. |
| 68 | */ |
| 69 | public static final TextDirectionHeuristic CHARCOUNT_RTL = |
| 70 | new TextDirectionHeuristicInternal(CharCount.INSTANCE_DEFAULT, true); |
| 71 | |
| 72 | private static enum TriState { |
| 73 | TRUE, FALSE, UNKNOWN; |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Computes the text direction based on an algorithm. Subclasses implement |
| 78 | * {@link #defaultIsRtl} to handle cases where the algorithm cannot determine the |
| 79 | * direction from the text alone. |
| 80 | * @hide |
| 81 | */ |
| 82 | public static abstract class TextDirectionHeuristicImpl implements TextDirectionHeuristic { |
| 83 | private final TextDirectionAlgorithm mAlgorithm; |
| 84 | |
| 85 | public TextDirectionHeuristicImpl(TextDirectionAlgorithm algorithm) { |
| 86 | mAlgorithm = algorithm; |
| 87 | } |
| 88 | |
| 89 | /** |
| 90 | * Return true if the default text direction is rtl. |
| 91 | */ |
| 92 | abstract protected boolean defaultIsRtl(); |
| 93 | |
| 94 | @Override |
| 95 | public boolean isRtl(CharSequence text, int start, int end) { |
| 96 | if (text == null || start < 0 || end < start || text.length() < end) { |
| 97 | throw new IllegalArgumentException(); |
| 98 | } |
| 99 | if (mAlgorithm == null) { |
| 100 | return defaultIsRtl(); |
| 101 | } |
| 102 | text = text.subSequence(start, end); |
| 103 | char[] chars = text.toString().toCharArray(); |
| 104 | return doCheck(chars, 0, chars.length); |
| 105 | } |
| 106 | |
| 107 | @Override |
| 108 | public boolean isRtl(char[] chars, int start, int count) { |
| 109 | if (chars == null || start < 0 || count < 0 || chars.length - count < start) { |
| 110 | throw new IllegalArgumentException(); |
| 111 | } |
| 112 | if (mAlgorithm == null) { |
| 113 | return defaultIsRtl(); |
| 114 | } |
| 115 | return doCheck(chars, start, count); |
| 116 | } |
| 117 | |
| 118 | private boolean doCheck(char[] chars, int start, int count) { |
| 119 | switch(mAlgorithm.checkRtl(chars, start, count)) { |
| 120 | case TRUE: |
| 121 | return true; |
| 122 | case FALSE: |
| 123 | return false; |
| 124 | default: |
| 125 | return defaultIsRtl(); |
| 126 | } |
| 127 | } |
| 128 | } |
| 129 | |
| 130 | private static class TextDirectionHeuristicInternal extends TextDirectionHeuristicImpl { |
| 131 | private final boolean mDefaultIsRtl; |
| 132 | |
| 133 | private TextDirectionHeuristicInternal(TextDirectionAlgorithm algorithm, |
| 134 | boolean defaultIsRtl) { |
| 135 | super(algorithm); |
| 136 | mDefaultIsRtl = defaultIsRtl; |
| 137 | } |
| 138 | |
| 139 | @Override |
| 140 | protected boolean defaultIsRtl() { |
| 141 | return mDefaultIsRtl; |
| 142 | } |
| 143 | } |
| 144 | |
| 145 | private static TriState isRtlText(int directionality) { |
| 146 | switch (directionality) { |
| 147 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT: |
| 148 | return TriState.FALSE; |
| 149 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT: |
| 150 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_ARABIC: |
| 151 | return TriState.TRUE; |
| 152 | default: |
| 153 | return TriState.UNKNOWN; |
| 154 | } |
| 155 | } |
| 156 | |
| 157 | private static TriState isRtlTextOrFormat(int directionality) { |
| 158 | switch (directionality) { |
| 159 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT: |
| 160 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT_EMBEDDING: |
| 161 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT_OVERRIDE: |
| 162 | return TriState.FALSE; |
| 163 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT: |
| 164 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_ARABIC: |
| 165 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_EMBEDDING: |
| 166 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_OVERRIDE: |
| 167 | return TriState.TRUE; |
| 168 | default: |
| 169 | return TriState.UNKNOWN; |
| 170 | } |
| 171 | } |
| 172 | |
| 173 | /** |
| 174 | * Interface for an algorithm to guess the direction of a paragraph of text. |
| 175 | * |
| 176 | * @hide |
| 177 | */ |
| 178 | public static interface TextDirectionAlgorithm { |
| 179 | /** |
| 180 | * Returns whether the range of text is RTL according to the algorithm. |
| 181 | * |
| 182 | * @hide |
| 183 | */ |
| 184 | TriState checkRtl(char[] text, int start, int count); |
| 185 | } |
| 186 | |
| 187 | /** |
| 188 | * Algorithm that uses the first strong directional character to determine |
| 189 | * the paragraph direction. This is the standard Unicode Bidirectional |
| 190 | * algorithm. |
| 191 | * |
| 192 | * @hide |
| 193 | */ |
| 194 | public static class FirstStrong implements TextDirectionAlgorithm { |
| 195 | @Override |
| 196 | public TriState checkRtl(char[] text, int start, int count) { |
| 197 | TriState result = TriState.UNKNOWN; |
| 198 | for (int i = start, e = start + count; i < e && result == TriState.UNKNOWN; ++i) { |
| 199 | result = isRtlTextOrFormat(Character.getDirectionality(text[i])); |
| 200 | } |
| 201 | return result; |
| 202 | } |
| 203 | |
| 204 | private FirstStrong() { |
| 205 | } |
| 206 | |
| 207 | public static final FirstStrong INSTANCE = new FirstStrong(); |
| 208 | } |
| 209 | |
| 210 | /** |
| 211 | * Algorithm that uses the presence of any strong directional non-format |
| 212 | * character (e.g. excludes LRE, LRO, RLE, RLO) to determine the |
| 213 | * direction of text. |
| 214 | * |
| 215 | * @hide |
| 216 | */ |
| 217 | public static class AnyStrong implements TextDirectionAlgorithm { |
| 218 | private final boolean mLookForRtl; |
| 219 | |
| 220 | @Override |
| 221 | public TriState checkRtl(char[] text, int start, int count) { |
| 222 | boolean haveUnlookedFor = false; |
| 223 | for (int i = start, e = start + count; i < e; ++i) { |
| 224 | switch (isRtlText(Character.getDirectionality(text[i]))) { |
| 225 | case TRUE: |
| 226 | if (mLookForRtl) { |
| 227 | return TriState.TRUE; |
| 228 | } |
| 229 | haveUnlookedFor = true; |
| 230 | break; |
| 231 | case FALSE: |
| 232 | if (!mLookForRtl) { |
| 233 | return TriState.FALSE; |
| 234 | } |
| 235 | haveUnlookedFor = true; |
| 236 | break; |
| 237 | default: |
| 238 | break; |
| 239 | } |
| 240 | } |
| 241 | if (haveUnlookedFor) { |
| 242 | return mLookForRtl ? TriState.FALSE : TriState.TRUE; |
| 243 | } |
| 244 | return TriState.UNKNOWN; |
| 245 | } |
| 246 | |
| 247 | private AnyStrong(boolean lookForRtl) { |
| 248 | this.mLookForRtl = lookForRtl; |
| 249 | } |
| 250 | |
| 251 | public static final AnyStrong INSTANCE_RTL = new AnyStrong(true); |
| 252 | public static final AnyStrong INSTANCE_LTR = new AnyStrong(false); |
| 253 | } |
| 254 | |
| 255 | /** |
| 256 | * Algorithm that uses the relative proportion of strong directional |
| 257 | * characters (excluding LRE, LRO, RLE, RLO) to determine the direction |
| 258 | * of the paragraph, if the proportion exceeds a given threshold. |
| 259 | * |
| 260 | * @hide |
| 261 | */ |
| 262 | public static class CharCount implements TextDirectionAlgorithm { |
| 263 | private final float mThreshold; |
| 264 | |
| 265 | @Override |
| 266 | public TriState checkRtl(char[] text, int start, int count) { |
| 267 | int countLtr = 0; |
| 268 | int countRtl = 0; |
| 269 | for(int i = start, e = start + count; i < e; ++i) { |
| 270 | switch (isRtlText(Character.getDirectionality(text[i]))) { |
| 271 | case TRUE: |
| 272 | ++countLtr; |
| 273 | break; |
| 274 | case FALSE: |
| 275 | ++countRtl; |
| 276 | break; |
| 277 | default: |
| 278 | break; |
| 279 | } |
| 280 | } |
| 281 | int limit = (int)((countLtr + countRtl) * mThreshold); |
| 282 | if (limit > 0) { |
| 283 | if (countLtr > limit) { |
| 284 | return TriState.FALSE; |
| 285 | } |
| 286 | if (countRtl > limit) { |
| 287 | return TriState.TRUE; |
| 288 | } |
| 289 | } |
| 290 | return TriState.UNKNOWN; |
| 291 | } |
| 292 | |
| 293 | private CharCount(float threshold) { |
| 294 | mThreshold = threshold; |
| 295 | } |
| 296 | |
| 297 | public static CharCount withThreshold(float threshold) { |
| 298 | if (threshold < 0 || threshold > 1) { |
| 299 | throw new IllegalArgumentException(); |
| 300 | } |
| 301 | if (threshold == DEFAULT_THRESHOLD) { |
| 302 | return INSTANCE_DEFAULT; |
| 303 | } |
| 304 | return new CharCount(threshold); |
| 305 | } |
| 306 | |
| 307 | public static final float DEFAULT_THRESHOLD = 0.6f; |
| 308 | public static final CharCount INSTANCE_DEFAULT = new CharCount(DEFAULT_THRESHOLD); |
| 309 | } |
| 310 | } |