Add hyphenation to line breaking

This patch adds hyphenation using the Liang hyphenation algorithm,
similar to TeX. It also improves the optimized line breaker so that
it works correctly and efficiently even when the line width is not
constant (there is a specialization for constant width, which is
probably worthwhile, but performance TODOs remain).

Still to be done:

* hyphenator has many shortcuts, only tested with English

* interaction between punctuation and hyphenation is problematic

Change-Id: I2d94a1668ebc536398b7c43fcf486333eeb7c6aa

1 files changed, 152 insertions, 0 deletions

diff --git a/libs/minikin/Hyphenator.cpp b/libs/minikin/Hyphenator.cpp
new file mode 100644
index 0000000..c50b386
--- /dev/null
+++ b/libs/minikin/Hyphenator.cpp
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vector>
+#include <memory>
+#include <cctype>
+#include <algorithm>
+#include <string>
+
+// HACK: for reading pattern file
+#include <fcntl.h>
+
+#define LOG_TAG "Minikin"
+#include "utils/Log.h"
+
+#include "minikin/Hyphenator.h"
+
+using std::vector;
+
+namespace android {
+
+static const uint16_t CHAR_SOFT_HYPHEN = 0x00AD;
+
+void Hyphenator::addPattern(const uint16_t* pattern, size_t size) {
+    vector<uint16_t> word;
+    vector<uint8_t> result;
+
+    // start by parsing the Liang-format pattern into a word and a result vector, the
+    // vector right-aligned but without leading zeros. Examples:
+    // a1bc2d -> abcd [1, 0, 2, 0]
+    // abc1 -> abc [1]
+    // 1a2b3c4d5 -> abcd [1, 2, 3, 4, 5]
+    bool lastWasLetter = false;
+    bool haveSeenNumber = false;
+    for (size_t i = 0; i < size; i++) {
+        uint16_t c = pattern[i];
+        if (isdigit(c)) {
+            result.push_back(c - '0');
+            lastWasLetter = false;
+            haveSeenNumber = true;
+        } else {
+            word.push_back(c);
+            if (lastWasLetter && haveSeenNumber) {
+                result.push_back(0);
+            }
+            lastWasLetter = true;
+        }
+    }
+    if (lastWasLetter) {
+        result.push_back(0);
+    }
+    Trie* t = &root;
+    for (size_t i = 0; i < word.size(); i++) {
+        t = &t->succ[word[i]];
+    }
+    t->result = result;
+}
+
+// If any soft hyphen is present in the word, use soft hyphens to decide hyphenation,
+// as recommended in UAX #14 (Use of Soft Hyphen)
+void Hyphenator::hyphenateSoft(vector<uint8_t>* result, const uint16_t* word, size_t len) {
+    (*result)[0] = 0;
+    for (size_t i = 1; i < len; i++) {
+        (*result)[i] = word[i - 1] == CHAR_SOFT_HYPHEN;
+    }
+}
+
+void Hyphenator::hyphenate(vector<uint8_t>* result, const uint16_t* word, size_t len) {
+    result->clear();
+    result->resize(len);
+    if (len < MIN_PREFIX + MIN_SUFFIX) return;
+    size_t maxOffset = len - MIN_SUFFIX + 1;
+    for (size_t i = 0; i < len + 1; i++) {
+        const Trie* node = &root;
+        for (size_t j = i; j < len + 2; j++) {
+            uint16_t c;
+            if (j == 0 || j == len + 1) {
+                c = '.';  // word boundary character in pattern data files
+            } else {
+                c = word[j - 1];
+                if (c == CHAR_SOFT_HYPHEN) {
+                    hyphenateSoft(result, word, len);
+                    return;
+                }
+                // TODO: use locale-sensitive case folding from ICU.
+                c = tolower(c);
+            }
+            auto search = node->succ.find(c);
+            if (search != node->succ.end()) {
+                node = &search->second;
+            } else {
+                break;
+            }
+            if (!node->result.empty()) {
+                int resultLen = node->result.size();
+                int offset = j + 1 - resultLen;
+                int start = std::max(MIN_PREFIX - offset, 0);
+                int end = std::min(resultLen, (int)maxOffset - offset);
+                // TODO performance: this inner loop can profitably be optimized
+                for (int k = start; k < end; k++) {
+                    (*result)[offset + k] = std::max((*result)[offset + k], node->result[k]);
+                }
+#if 0
+                // debug printing of matched patterns
+                std::string dbg;
+                for (size_t k = i; k <= j + 1; k++) {
+                    int off = k - j - 2 + resultLen;
+                    if (off >= 0 && node->result[off] != 0) {
+                        dbg.push_back((char)('0' + node->result[off]));
+                    }
+                    if (k < j + 1) {
+                        uint16_t c = (k == 0 || k == len + 1) ? '.' : word[k - 1];
+                        dbg.push_back((char)c);
+                    }
+                }
+                ALOGD("%d:%d %s", i, j, dbg.c_str());
+#endif
+            }
+        }
+    }
+    // Since the above calculation does not modify values outside
+    // [MIN_PREFIX, len - MIN_SUFFIX], they are left as 0.
+    for (size_t i = MIN_PREFIX; i < maxOffset; i++) {
+        (*result)[i] &= 1;
+    }
+}
+
+Hyphenator* Hyphenator::load(const uint16_t *patternData, size_t size) {
+    Hyphenator* result = new Hyphenator;
+    for (size_t i = 0; i < size; i++) {
+        size_t end = i;
+        while (patternData[end] != '\n') end++;
+        result->addPattern(patternData + i, end - i);
+        i = end;
+    }
+    return result;
+}
+
+}  // namespace android