Extract metrics from the OS/2 table

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/Graphics/Fountainhead/TrueType.hs b/lib/Graphics/Fountainhead/TrueType.hs
index 55d55ae..03852b5 100644
--- a/lib/Graphics/Fountainhead/TrueType.hs
+++ b/lib/Graphics/Fountainhead/TrueType.hs
@@ -4,7 +4,10 @@
 
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE ViewPatterns #-}
 
 -- | Types representing a TrueType font.
 module Graphics.Fountainhead.TrueType
@@ -85,6 +88,7 @@ module Graphics.Fountainhead.TrueType
     , findTableByTag
     , unLocaTable
     , nameStringOffset
+    , pattern Os2Version4CommonFields
     ) where
 
 import Data.ByteString (ByteString)
@@ -545,6 +549,21 @@ data Os2Table
     | Os2Version5 Os2BaseFields Os2MicrosoftFields Os2Version5Fields
     deriving (Eq, Show)
 
+pattern Os2Version4CommonFields :: Os2BaseFields -> Os2Version4Fields -> Os2Table
+pattern Os2Version4CommonFields baseFields versionFields <-
+    (os2Version4CommonFields -> Just (baseFields, versionFields))
+
+{-# COMPLETE Os2Version4CommonFields, Os2Version0, Os2Version1, Os2Version5 #-}
+
+os2Version4CommonFields :: Os2Table -> Maybe (Os2BaseFields, Os2Version4Fields)
+os2Version4CommonFields = \case
+    Os2Version0{} -> Nothing
+    Os2Version1{} -> Nothing
+    Os2Version2 baseFields _ versionFields -> Just (baseFields, versionFields)
+    Os2Version3 baseFields _ versionFields -> Just (baseFields, versionFields)
+    Os2Version4 baseFields _ versionFields -> Just (baseFields, versionFields)
+    Os2Version5{} -> Nothing
+
 data Os2Version1Fields = Os2Version1Fields
     { ulCodePageRange1 :: Word32
     , ulCodePageRange2 :: Word32