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{- 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 #-}
{-# LANGUAGE PatternSynonyms #-}
module Graphics.Fountainhead.Metrics
( FontBBox(..)
, FontDescriptor(..)
, MetricsError(..)
, Number
, FontDescriptorFlag(..)
, collectMetrics
) where
import Data.ByteString (ByteString)
import Data.List (findIndex)
import qualified Data.List.NonEmpty as NonEmpty
import Data.Text (Text)
import qualified Data.Text.Encoding as Text
import Graphics.Fountainhead.TrueType
( BSerifStyle(..)
, FontDirectory(..)
, HeadTable(..)
, HheaTable(..)
, HmtxTable(..)
, LongHorMetric(..)
, NameRecord(..)
, NameTable(..)
, Os2BaseFields(..)
, Os2Version4Fields(..)
, Os2Version5Fields(..)
, Os2Table(..)
, Panose(..)
, PostHeader(..)
, PostTable(..)
, findTableByTag
, pattern Os2Version4CommonFields
)
import Graphics.Fountainhead.Parser
( Parser
, ParseErrorBundle
, ParseState
, nameTableP
, parseFontDirectory
, parseTable
, headTableP
, hheaTableP
, hmtxTableP
, os2TableP
, postTableP
)
import qualified Text.Megaparsec as Megaparsec
import Data.Bifunctor (Bifunctor(..))
import Data.Int (Int16)
import Data.Word (Word16)
import GHC.Records (HasField(..))
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
| UnsupportedOs2VersionError
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."
show UnsupportedOs2VersionError =
"OS/2 version 1 does not contain cap height."
collectMetrics :: FilePath -> ByteString -> Either MetricsError FontDescriptor
collectMetrics fontFile ttfContents =
case parseFontDirectory fontFile ttfContents of
(_processedState, Left initialResult) -> Left
$ MetricsParseError initialResult
(processedState, Right initialResult) -> do
let parseForMetrics' :: String -> Parser a -> Either MetricsError a
parseForMetrics' = parseForMetrics processedState initialResult
NameTable{ nameRecord, variable } <- parseForMetrics' "name" nameTableP
psNameIndex <- maybeMetricsError (MetricsNameRecordNotFound 6)
$ findIndex ((6 ==) . getField @"nameID") nameRecord
headTable@HeadTable{ unitsPerEm } <- parseForMetrics' "head" headTableP
let scale = (1000.0 :: Float) / fromIntegral unitsPerEm
HheaTable{ ascent, descent, numOfLongHorMetrics } <-
parseForMetrics' "hhea" hheaTableP
PostTable{ postHeader } <- parseForMetrics' "post" postTableP
(capHeight, os2BaseFields) <- getCapHeight processedState initialResult
let Os2BaseFields{ usWeightClass, panose } = os2BaseFields
HmtxTable{ hMetrics } <- parseForMetrics' "hmtx"
$ hmtxTableP numOfLongHorMetrics
let fixedPitchFlag = if getField @"isFixedPitch" postHeader > 0 then Just FixedPitch else Nothing
isSerifFlag = if isSerif $ getField @"bSerifStyle" panose then Just Serif else Nothing
pure $ FontDescriptor
{ fontName = variableText nameRecord variable psNameIndex
, flags = []
, stemV = calculateStemV $ fromIntegral usWeightClass
, missingWidth = fromIntegral $ scalePs scale
$ getField @"advanceWidth" $ NonEmpty.head hMetrics
, fontBBox = calculateBoundingBox scale headTable
, italicAngle = realToFrac $ getField @"italicAngle" postHeader
, capHeight = fromIntegral $ scalePs scale capHeight
, ascender = fromIntegral $ scalePs scale ascent
, descender = fromIntegral $ scalePs scale descent
}
where
calculateStemV weightClass = 10 + 220 * (weightClass - 50) / 900
getCapHeight processedState initialResult = do
os2Table <- parseForMetrics processedState initialResult "OS/2" os2TableP
case os2Table of
Os2Version4CommonFields os2BaseFields Os2Version4Fields{ sCapHeight } ->
Right (sCapHeight, os2BaseFields)
Os2Version5 os2BaseFields _ Os2Version5Fields{ sCapHeight } ->
Right (sCapHeight, os2BaseFields)
_ -> Left UnsupportedOs2VersionError
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 :: Integral a => Float -> a -> 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
parseForMetrics
:: forall a
. ParseState
-> FontDirectory
-> String
-> Parser a
-> Either MetricsError a
parseForMetrics processedState fontDirectory tableName tableParser =
let foundTable = findTableByTag tableName fontDirectory
missingError = MetricsRequiredTableMissingError tableName
parseTable' rawTable = parseTable rawTable tableParser processedState
in maybeMetricsError missingError foundTable
>>= first MetricsParseError . parseTable'
maybeMetricsError :: forall a. MetricsError -> Maybe a -> Either MetricsError a
maybeMetricsError metricsError Nothing = Left metricsError
maybeMetricsError _ (Just result) = Right result
isSerif :: BSerifStyle -> Bool
isSerif AnySerifStyle = False
isSerif NoFitSerifStyle = False
isSerif CoveSerifStyle = True
isSerif ObtuseCoveSerifStyle = True
isSerif SquareCoveSerifStyle = True
isSerif ObtuseSquareCoveSerifStyle = True
isSerif SquareSerifStyle = True
isSerif ThinSerifStyle = True
isSerif BoneSerifStyle = True
isSerif ExaggeratedSerifStyle =True
isSerif TriangleSerifStyle = True
isSerif NormalSansSerifStyle = False
isSerif ObtuseSansSerifStyle = False
isSerif PerpSansSerifStyle = False
isSerif FlaredSerifStyle = True
isSerif RoundedSerifStyle = True
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