Fabrice Di Meglio | 4b60c30 | 2011-08-17 16:56:55 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2011 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 16 | |
| 17 | package android.text; |
| 18 | |
| 19 | |
Fabrice Di Meglio | 3fb824b | 2012-02-28 17:58:31 -0800 | [diff] [blame] | 20 | import android.view.View; |
Fabrice Di Meglio | 7810b5f | 2011-08-24 18:26:14 -0700 | [diff] [blame] | 21 | |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 22 | /** |
| 23 | * Some objects that implement TextDirectionHeuristic. |
Gilles Debunne | cefb4bc | 2012-05-02 18:14:56 -0700 | [diff] [blame] | 24 | * |
| 25 | * @hide |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 26 | */ |
| 27 | public class TextDirectionHeuristics { |
| 28 | |
| 29 | /** Always decides that the direction is left to right. */ |
| 30 | public static final TextDirectionHeuristic LTR = |
| 31 | new TextDirectionHeuristicInternal(null /* no algorithm */, false); |
| 32 | |
| 33 | /** Always decides that the direction is right to left. */ |
| 34 | public static final TextDirectionHeuristic RTL = |
| 35 | new TextDirectionHeuristicInternal(null /* no algorithm */, true); |
| 36 | |
| 37 | /** |
| 38 | * Determines the direction based on the first strong directional character, |
| 39 | * including bidi format chars, falling back to left to right if it |
| 40 | * finds none. This is the default behavior of the Unicode Bidirectional |
| 41 | * Algorithm. |
| 42 | */ |
| 43 | public static final TextDirectionHeuristic FIRSTSTRONG_LTR = |
| 44 | new TextDirectionHeuristicInternal(FirstStrong.INSTANCE, false); |
| 45 | |
| 46 | /** |
| 47 | * Determines the direction based on the first strong directional character, |
| 48 | * including bidi format chars, falling back to right to left if it |
| 49 | * finds none. This is similar to the default behavior of the Unicode |
| 50 | * Bidirectional Algorithm, just with different fallback behavior. |
| 51 | */ |
| 52 | public static final TextDirectionHeuristic FIRSTSTRONG_RTL = |
| 53 | new TextDirectionHeuristicInternal(FirstStrong.INSTANCE, true); |
| 54 | |
| 55 | /** |
Fabrice Di Meglio | 4b60c30 | 2011-08-17 16:56:55 -0700 | [diff] [blame] | 56 | * If the text contains any strong right to left non-format character, determines |
| 57 | * that the direction is right to left, falling back to left to right if it |
| 58 | * finds none. |
| 59 | */ |
| 60 | public static final TextDirectionHeuristic ANYRTL_LTR = |
| 61 | new TextDirectionHeuristicInternal(AnyStrong.INSTANCE_RTL, false); |
| 62 | |
| 63 | /** |
Fabrice Di Meglio | 7810b5f | 2011-08-24 18:26:14 -0700 | [diff] [blame] | 64 | * Force the paragraph direction to the Locale direction. Falls back to left to right. |
| 65 | */ |
| 66 | public static final TextDirectionHeuristic LOCALE = TextDirectionHeuristicLocale.INSTANCE; |
| 67 | |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 68 | private static enum TriState { |
| 69 | TRUE, FALSE, UNKNOWN; |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Computes the text direction based on an algorithm. Subclasses implement |
| 74 | * {@link #defaultIsRtl} to handle cases where the algorithm cannot determine the |
| 75 | * direction from the text alone. |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 76 | */ |
Fabrice Di Meglio | e7beae3 | 2012-02-13 15:23:57 -0800 | [diff] [blame] | 77 | private static abstract class TextDirectionHeuristicImpl implements TextDirectionHeuristic { |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 78 | private final TextDirectionAlgorithm mAlgorithm; |
| 79 | |
| 80 | public TextDirectionHeuristicImpl(TextDirectionAlgorithm algorithm) { |
| 81 | mAlgorithm = algorithm; |
| 82 | } |
| 83 | |
| 84 | /** |
| 85 | * Return true if the default text direction is rtl. |
| 86 | */ |
| 87 | abstract protected boolean defaultIsRtl(); |
| 88 | |
| 89 | @Override |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 90 | public boolean isRtl(char[] chars, int start, int count) { |
| 91 | if (chars == null || start < 0 || count < 0 || chars.length - count < start) { |
| 92 | throw new IllegalArgumentException(); |
| 93 | } |
| 94 | if (mAlgorithm == null) { |
| 95 | return defaultIsRtl(); |
| 96 | } |
| 97 | return doCheck(chars, start, count); |
| 98 | } |
| 99 | |
| 100 | private boolean doCheck(char[] chars, int start, int count) { |
| 101 | switch(mAlgorithm.checkRtl(chars, start, count)) { |
| 102 | case TRUE: |
| 103 | return true; |
| 104 | case FALSE: |
| 105 | return false; |
| 106 | default: |
| 107 | return defaultIsRtl(); |
| 108 | } |
| 109 | } |
| 110 | } |
| 111 | |
| 112 | private static class TextDirectionHeuristicInternal extends TextDirectionHeuristicImpl { |
| 113 | private final boolean mDefaultIsRtl; |
| 114 | |
| 115 | private TextDirectionHeuristicInternal(TextDirectionAlgorithm algorithm, |
| 116 | boolean defaultIsRtl) { |
| 117 | super(algorithm); |
| 118 | mDefaultIsRtl = defaultIsRtl; |
| 119 | } |
| 120 | |
| 121 | @Override |
| 122 | protected boolean defaultIsRtl() { |
| 123 | return mDefaultIsRtl; |
| 124 | } |
| 125 | } |
| 126 | |
| 127 | private static TriState isRtlText(int directionality) { |
| 128 | switch (directionality) { |
| 129 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT: |
| 130 | return TriState.FALSE; |
| 131 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT: |
| 132 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_ARABIC: |
| 133 | return TriState.TRUE; |
| 134 | default: |
| 135 | return TriState.UNKNOWN; |
| 136 | } |
| 137 | } |
| 138 | |
| 139 | private static TriState isRtlTextOrFormat(int directionality) { |
| 140 | switch (directionality) { |
| 141 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT: |
| 142 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT_EMBEDDING: |
| 143 | case Character.DIRECTIONALITY_LEFT_TO_RIGHT_OVERRIDE: |
| 144 | return TriState.FALSE; |
| 145 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT: |
| 146 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_ARABIC: |
| 147 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_EMBEDDING: |
| 148 | case Character.DIRECTIONALITY_RIGHT_TO_LEFT_OVERRIDE: |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 149 | return TriState.TRUE; |
| 150 | default: |
| 151 | return TriState.UNKNOWN; |
| 152 | } |
| 153 | } |
| 154 | |
| 155 | /** |
| 156 | * Interface for an algorithm to guess the direction of a paragraph of text. |
| 157 | * |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 158 | */ |
Fabrice Di Meglio | e7beae3 | 2012-02-13 15:23:57 -0800 | [diff] [blame] | 159 | private static interface TextDirectionAlgorithm { |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 160 | /** |
| 161 | * Returns whether the range of text is RTL according to the algorithm. |
| 162 | * |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 163 | */ |
| 164 | TriState checkRtl(char[] text, int start, int count); |
| 165 | } |
| 166 | |
| 167 | /** |
| 168 | * Algorithm that uses the first strong directional character to determine |
| 169 | * the paragraph direction. This is the standard Unicode Bidirectional |
| 170 | * algorithm. |
| 171 | * |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 172 | */ |
Fabrice Di Meglio | e7beae3 | 2012-02-13 15:23:57 -0800 | [diff] [blame] | 173 | private static class FirstStrong implements TextDirectionAlgorithm { |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 174 | @Override |
| 175 | public TriState checkRtl(char[] text, int start, int count) { |
| 176 | TriState result = TriState.UNKNOWN; |
| 177 | for (int i = start, e = start + count; i < e && result == TriState.UNKNOWN; ++i) { |
| 178 | result = isRtlTextOrFormat(Character.getDirectionality(text[i])); |
| 179 | } |
| 180 | return result; |
| 181 | } |
| 182 | |
| 183 | private FirstStrong() { |
| 184 | } |
| 185 | |
| 186 | public static final FirstStrong INSTANCE = new FirstStrong(); |
| 187 | } |
| 188 | |
| 189 | /** |
| 190 | * Algorithm that uses the presence of any strong directional non-format |
| 191 | * character (e.g. excludes LRE, LRO, RLE, RLO) to determine the |
| 192 | * direction of text. |
| 193 | * |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 194 | */ |
Fabrice Di Meglio | e7beae3 | 2012-02-13 15:23:57 -0800 | [diff] [blame] | 195 | private static class AnyStrong implements TextDirectionAlgorithm { |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 196 | private final boolean mLookForRtl; |
| 197 | |
| 198 | @Override |
| 199 | public TriState checkRtl(char[] text, int start, int count) { |
| 200 | boolean haveUnlookedFor = false; |
| 201 | for (int i = start, e = start + count; i < e; ++i) { |
| 202 | switch (isRtlText(Character.getDirectionality(text[i]))) { |
| 203 | case TRUE: |
| 204 | if (mLookForRtl) { |
| 205 | return TriState.TRUE; |
| 206 | } |
| 207 | haveUnlookedFor = true; |
| 208 | break; |
| 209 | case FALSE: |
| 210 | if (!mLookForRtl) { |
| 211 | return TriState.FALSE; |
| 212 | } |
| 213 | haveUnlookedFor = true; |
| 214 | break; |
| 215 | default: |
| 216 | break; |
| 217 | } |
| 218 | } |
| 219 | if (haveUnlookedFor) { |
| 220 | return mLookForRtl ? TriState.FALSE : TriState.TRUE; |
| 221 | } |
| 222 | return TriState.UNKNOWN; |
| 223 | } |
| 224 | |
| 225 | private AnyStrong(boolean lookForRtl) { |
| 226 | this.mLookForRtl = lookForRtl; |
| 227 | } |
| 228 | |
| 229 | public static final AnyStrong INSTANCE_RTL = new AnyStrong(true); |
| 230 | public static final AnyStrong INSTANCE_LTR = new AnyStrong(false); |
| 231 | } |
| 232 | |
| 233 | /** |
Fabrice Di Meglio | 7810b5f | 2011-08-24 18:26:14 -0700 | [diff] [blame] | 234 | * Algorithm that uses the Locale direction to force the direction of a paragraph. |
| 235 | */ |
Fabrice Di Meglio | e7beae3 | 2012-02-13 15:23:57 -0800 | [diff] [blame] | 236 | private static class TextDirectionHeuristicLocale extends TextDirectionHeuristicImpl { |
Fabrice Di Meglio | 7810b5f | 2011-08-24 18:26:14 -0700 | [diff] [blame] | 237 | |
| 238 | public TextDirectionHeuristicLocale() { |
| 239 | super(null); |
| 240 | } |
| 241 | |
| 242 | @Override |
| 243 | protected boolean defaultIsRtl() { |
Fabrice Di Meglio | d3d9f3f | 2012-09-18 12:55:32 -0700 | [diff] [blame^] | 244 | final int dir = TextUtils.getLayoutDirectionFromLocale(java.util.Locale.getDefault()); |
Fabrice Di Meglio | 3fb824b | 2012-02-28 17:58:31 -0800 | [diff] [blame] | 245 | return (dir == View.LAYOUT_DIRECTION_RTL); |
Fabrice Di Meglio | 7810b5f | 2011-08-24 18:26:14 -0700 | [diff] [blame] | 246 | } |
| 247 | |
| 248 | public static final TextDirectionHeuristicLocale INSTANCE = |
| 249 | new TextDirectionHeuristicLocale(); |
| 250 | } |
Doug Felt | cb379120 | 2011-07-07 11:57:48 -0700 | [diff] [blame] | 251 | } |