LayoutUtils.cpp revision 9b0b003dc15c6741ddf164d1aa39965110b79b80 
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#include "LayoutUtils.h"
18
19namespace minikin {
20
21/*
22 * Determine whether the code unit is a word space for the purposes of justification.
23 * TODO: Support NBSP and other stretchable whitespace (b/34013491 and b/68204709).
24 */
25bool isWordSpace(uint16_t code_unit) {
26    return code_unit == ' ';
27}
28
29/**
30 * For the purpose of layout, a word break is a boundary with no
31 * kerning or complex script processing. This is necessarily a
32 * heuristic, but should be accurate most of the time.
33 */
34static bool isWordBreakAfter(uint16_t c) {
35    if (c == ' ' || (0x2000 <= c && c <= 0x200A) || c == 0x3000) {
36        // spaces
37        return true;
38    }
39    // Note: kana is not included, as sophisticated fonts may kern kana
40    return false;
41}
42
43static bool isWordBreakBefore(uint16_t c) {
44    // CJK ideographs (and yijing hexagram symbols)
45    return isWordBreakAfter(c) || (0x3400 <= c && c <= 0x9FFF);
46}
47
48/**
49 * Return offset of previous word break. It is either < offset or == 0.
50 */
51size_t getPrevWordBreakForCache(const uint16_t* chars, size_t offset, size_t len) {
52    if (offset == 0) return 0;
53    if (offset > len) offset = len;
54    if (isWordBreakBefore(chars[offset - 1])) {
55        return offset - 1;
56    }
57    for (size_t i = offset - 1; i > 0; i--) {
58        if (isWordBreakBefore(chars[i]) || isWordBreakAfter(chars[i - 1])) {
59            return i;
60        }
61    }
62    return 0;
63}
64
65/**
66 * Return offset of next word break. It is either > offset or == len.
67 */
68size_t getNextWordBreakForCache(const uint16_t* chars, size_t offset, size_t len) {
69    if (offset >= len) return len;
70    if (isWordBreakAfter(chars[offset])) {
71        return offset + 1;
72    }
73    for (size_t i = offset + 1; i < len; i++) {
74        // No need to check isWordBreakAfter(chars[i - 1]) since it is checked
75        // in previous iteration.  Note that isWordBreakBefore returns true
76        // whenever isWordBreakAfter returns true.
77        if (isWordBreakBefore(chars[i])) {
78            return i;
79        }
80    }
81    return len;
82}
83
84}  // namespace minikin
85