LayoutUtils.cpp revision 510047d8fd99c960d131c701bdee217d1970987f 
1/*
2 * Copyright (C) 2015 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 */
16
17#define LOG_TAG "Minikin"
18
19#include "LayoutUtils.h"
20
21namespace minikin {
22
23const uint16_t CHAR_NBSP = 0x00A0;
24
25/*
26 * Determine whether the code unit is a word space for the purposes of justification.
27 */
28bool isWordSpace(uint16_t code_unit) {
29    return code_unit == ' ' || code_unit == CHAR_NBSP;
30}
31
32/**
33 * For the purpose of layout, a word break is a boundary with no
34 * kerning or complex script processing. This is necessarily a
35 * heuristic, but should be accurate most of the time.
36 */
37static bool isWordBreakAfter(uint16_t c) {
38    if (c == ' ' || (0x2000 <= c && c <= 0x200A) || c == 0x3000) {
39        // spaces
40        return true;
41    }
42    // Note: kana is not included, as sophisticated fonts may kern kana
43    return false;
44}
45
46static bool isWordBreakBefore(uint16_t c) {
47    // CJK ideographs (and yijing hexagram symbols)
48    return isWordBreakAfter(c) || (0x3400 <= c && c <= 0x9FFF);
49}
50
51/**
52 * Return offset of previous word break. It is either < offset or == 0.
53 */
54size_t getPrevWordBreakForCache(
55        const uint16_t* chars, size_t offset, size_t len) {
56    if (offset == 0) return 0;
57    if (offset > len) offset = len;
58    if (isWordBreakBefore(chars[offset - 1])) {
59        return offset - 1;
60    }
61    for (size_t i = offset - 1; i > 0; i--) {
62        if (isWordBreakBefore(chars[i]) || isWordBreakAfter(chars[i - 1])) {
63            return i;
64        }
65    }
66    return 0;
67}
68
69/**
70 * Return offset of next word break. It is either > offset or == len.
71 */
72size_t getNextWordBreakForCache(
73        const uint16_t* chars, size_t offset, size_t len) {
74    if (offset >= len) return len;
75    if (isWordBreakAfter(chars[offset])) {
76        return offset + 1;
77    }
78    for (size_t i = offset + 1; i < len; i++) {
79        // No need to check isWordBreakAfter(chars[i - 1]) since it is checked
80        // in previous iteration.  Note that isWordBreakBefore returns true
81        // whenever isWordBreakAfter returns true.
82        if (isWordBreakBefore(chars[i])) {
83            return i;
84        }
85    }
86    return len;
87}
88
89}  // namespace minikin
90