1 /*
2 * Copyright 2019 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 package androidx.compose.ui.text.font
17
18 private const val AllFlags = 0xffff
19 private const val WeightFlag = 0x1
20 private const val StyleFlag = 0x2
21
22 /**
23 * Possible options for font synthesis.
24 *
25 * `FontSynthesis` is used to specify whether the system should fake bold or slanted glyphs when the
26 * [FontFamily] used does not contain bold or oblique [Font]s.
27 *
28 * If the font family does not include a requested [FontWeight] or [FontStyle], the system fakes
29 * bold or slanted glyphs when the [Weight] or [Style], respectively, or both when [All] is set. If
30 * this is not desired, use [None] to disable font synthesis.
31 *
32 * It is possible to fake an increase of [FontWeight] but not a decrease. It is possible to fake a
33 * regular font slanted, but not vice versa.
34 *
35 * `FontSynthesis` works the same way as the
36 * [CSS font-synthesis](https://www.w3.org/TR/css-fonts-4/#font-synthesis) property.
37 *
38 * @sample androidx.compose.ui.text.samples.FontFamilySynthesisSample
39 */
40 @kotlin.jvm.JvmInline
41 value class FontSynthesis internal constructor(internal val value: Int) {
42
toStringnull43 override fun toString(): String {
44 return when (this) {
45 None -> "None"
46 Weight -> "Weight"
47 Style -> "Style"
48 All -> "All"
49 else -> "Invalid"
50 }
51 }
52
53 // NOTE: The values below are selected to be used as flags. See isWeightOn for instance.
54 companion object {
55 /**
56 * Turns off font synthesis. Neither bold nor slanted faces are synthesized if they don't
57 * exist in the [FontFamily]
58 */
59 val None = FontSynthesis(0)
60
61 /**
62 * Only a bold font is synthesized, if it is not available in the [FontFamily]. Slanted
63 * fonts will not be synthesized.
64 */
65 val Weight = FontSynthesis(WeightFlag)
66
67 /**
68 * Only an slanted font is synthesized, if it is not available in the [FontFamily]. Bold
69 * fonts will not be synthesized.
70 */
71 val Style = FontSynthesis(StyleFlag)
72
73 /**
74 * The system synthesizes both bold and slanted fonts if either of them are not available in
75 * the [FontFamily]
76 */
77 val All = FontSynthesis(AllFlags)
78 }
79
80 internal val isWeightOn: Boolean
81 get() = value and WeightFlag != 0
82
83 internal val isStyleOn: Boolean
84 get() = value and StyleFlag != 0
85 }
86
87 /**
88 * Perform platform-specific font synthesis such as fake bold or fake italic.
89 *
90 * Platforms are not required to support synthesis, in which case they should return [typeface].
91 *
92 * Platforms that support synthesis should check [FontSynthesis.isWeightOn] and
93 * [FontSynthesis.isStyleOn] in this method before synthesizing bold or italic, respectively.
94 *
95 * @param typeface a platform-specific typeface
96 * @param font initial font that generated the typeface via loading
97 * @param requestedWeight app-requested weight (may be different than the font's weight)
98 * @param requestedStyle app-requested style (may be different than the font's style)
99 * @return a synthesized typeface, or the passed [typeface] if synthesis is not needed or supported.
100 */
synthesizeTypefacenull101 internal expect fun FontSynthesis.synthesizeTypeface(
102 typeface: Any,
103 font: Font,
104 requestedWeight: FontWeight,
105 requestedStyle: FontStyle
106 ): Any
107