1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
{- This Source Code Form is subject to the terms of the Mozilla Public License,
v. 2.0. If a copy of the MPL was not distributed with this file, You can
obtain one at https://mozilla.org/MPL/2.0/. -}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE DuplicateRecordFields #-}
module Graphics.Fountainhead.Metrics
( FontBBox(..)
, FontDescriptor(..)
, MetricsError(..)
, Number
, FontDescriptorFlag(..)
, collectMetrics
) where
import Data.ByteString (ByteString)
import Data.List (findIndex)
import Data.Text (Text)
import qualified Data.Text.Encoding as Text
import Graphics.Fountainhead.TrueType
( HeadTable(..)
, HheaTable(..)
, NameRecord(..)
, NameTable(..)
, PostHeader(..)
, PostTable(..)
, findTableByTag
)
import Graphics.Fountainhead.Parser
( ParseErrorBundle
, nameTableP
, parseFontDirectory
, parseTable
, headTableP
, hheaTableP
, postTableP
)
import qualified Text.Megaparsec as Megaparsec
import Data.Bifunctor (Bifunctor(..))
import Data.Int (Int16, Int32)
import Data.Word (Word16)
import GHC.Records (HasField(..))
import Graphics.Fountainhead.Type (Fixed32(..))
type Number = Float
data FontDescriptorFlag
= FixedPitch
| Serif
| Symbolic
| Script
| Nonsymbolic
| Italic
| AllCap
| SmallCap
| ForceBold
deriving (Eq, Show)
instance Enum FontDescriptorFlag
where
toEnum 1 = FixedPitch
toEnum 2 = Serif
toEnum 3 = Symbolic
toEnum 4 = Script
toEnum 6 = Nonsymbolic
toEnum 7 = Italic
toEnum 17 = AllCap
toEnum 18 = SmallCap
toEnum 19 = ForceBold
toEnum _ = error "Font description flag is not supported."
fromEnum FixedPitch = 1
fromEnum Serif = 2
fromEnum Symbolic = 3
fromEnum Script = 4
fromEnum Nonsymbolic = 6
fromEnum Italic = 7
fromEnum AllCap = 17
fromEnum SmallCap = 18
fromEnum ForceBold = 19
data FontBBox = FontBBox Number Number Number Number
deriving (Eq, Show)
data FontDescriptor = FontDescriptor
{ fontName :: Text
, flags :: [FontDescriptorFlag]
, stemV :: Number
, missingWidth :: Number
, fontBBox :: FontBBox
, italicAngle :: Number
, capHeight :: Number
, ascender :: Number
, descender :: Number
} deriving (Eq, Show)
data MetricsError
= MetricsParseError ParseErrorBundle
| MetricsRequiredTableMissingError String
| MetricsNameRecordNotFound Word16
deriving Eq
instance Show MetricsError
where
show (MetricsParseError errorBundle) = Megaparsec.errorBundlePretty errorBundle
show (MetricsRequiredTableMissingError tableName) =
"Required table " <> tableName <> " is missing."
show (MetricsNameRecordNotFound nameId) =
"Name record with ID " <> show nameId <> " was not found."
collectMetrics :: FilePath -> ByteString -> Either MetricsError FontDescriptor
collectMetrics fontFile ttfContents =
case parseFontDirectory fontFile ttfContents of
(_processedState, Left initialResult) -> Left
$ MetricsParseError initialResult
(processedState, Right initialResult) -> do
nameEntry <- maybeMetricsError (MetricsRequiredTableMissingError "name")
$ findTableByTag "name" initialResult
NameTable{ nameRecord, variable } <- first MetricsParseError
$ parseTable nameEntry nameTableP processedState
psNameIndex <- maybeMetricsError (MetricsNameRecordNotFound 6)
$ findIndex ((6 ==) . getField @"nameID") nameRecord
headEntry <- maybeMetricsError (MetricsRequiredTableMissingError "head")
$ findTableByTag "head" initialResult
headTable@HeadTable{ unitsPerEm } <- first MetricsParseError
$ parseTable headEntry headTableP processedState
let scale = (1000.0 :: Float) / fromIntegral unitsPerEm
hheaEntry <- maybeMetricsError (MetricsRequiredTableMissingError "hhea")
$ findTableByTag "hhea" initialResult
HheaTable{ ascent, descent } <- first MetricsParseError
$ parseTable hheaEntry hheaTableP processedState
postEntry <- maybeMetricsError (MetricsRequiredTableMissingError "post")
$ findTableByTag "post" initialResult
PostTable{ postHeader } <- first MetricsParseError
$ parseTable postEntry postTableP processedState
pure $ FontDescriptor
{ fontName = variableText nameRecord variable psNameIndex
, flags = []
, stemV = 1
, missingWidth = 0
, fontBBox = calculateBoundingBox scale headTable
, italicAngle = realToFrac $ getField @"italicAngle" postHeader
, capHeight = 0
, ascender = fromIntegral $ scalePs scale ascent
, descender = fromIntegral $ scalePs scale descent
}
where
calculateBoundingBox scale HeadTable{ xMin, xMax, yMin, yMax } =
let xMin' = fromIntegral $ scalePs scale xMin
yMin' = fromIntegral $ scalePs scale yMin
xMax' = fromIntegral $ scalePs scale xMax
yMax' = fromIntegral $ scalePs scale yMax
in FontBBox xMin' yMin' xMax' yMax'
scalePs :: Float -> Int16 -> Int16
scalePs scale value = truncate $ fromIntegral value * scale
variableText records variables recordIndex =
let NameRecord{ platformID } = records !! recordIndex
variable = variables !! recordIndex
in if platformID == 1
then Text.decodeUtf8 variable
else Text.decodeUtf16BE variable
maybeMetricsError metricsError Nothing = Left metricsError
maybeMetricsError _ (Just result) = Right result
|
