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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 Data.Text (Text)
import qualified Data.Text.Encoding as Text
import Graphics.Fountainhead.TrueType
( HeadTable(..)
, HheaTable(..)
, NameRecord(..)
, NameTable(..)
, Os2BaseFields(..)
, Os2Version4Fields(..)
, Os2Version5Fields(..)
, Os2Table(..)
, PostHeader(..)
, PostTable(..)
, findTableByTag
, pattern Os2Version4CommonFields
)
import Graphics.Fountainhead.Parser
( ParseErrorBundle
, nameTableP
, parseFontDirectory
, parseTable
, headTableP
, hheaTableP
, 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
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
(capHeight, weightClass) <- getCapHeight processedState initialResult
pure $ FontDescriptor
{ fontName = variableText nameRecord variable psNameIndex
, flags = []
, stemV = calculateStemV $ fromIntegral weightClass
, missingWidth = 0
, 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
os2Entry <- maybeMetricsError (MetricsRequiredTableMissingError "OS/2")
$ findTableByTag "OS/2" initialResult
os2Table <- first MetricsParseError
$ parseTable os2Entry os2TableP processedState
case os2Table of
Os2Version4CommonFields Os2BaseFields{ usWeightClass } Os2Version4Fields{ sCapHeight } ->
Right (sCapHeight, usWeightClass)
Os2Version5 Os2BaseFields{ usWeightClass } _ Os2Version5Fields{ sCapHeight } ->
Right (sCapHeight, usWeightClass)
_ -> 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 :: 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
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