diff --git a/src/Graphics/Fountainhead/Dumper.hs b/src/Graphics/Fountainhead/Dumper.hs
index 680c0f7..e7c6156 100644
--- a/src/Graphics/Fountainhead/Dumper.hs
+++ b/src/Graphics/Fountainhead/Dumper.hs
@@ -18,11 +18,13 @@ module Graphics.Fountainhead.Dumper
 
 import Data.ByteString (ByteString)
 import Data.Int (Int64)
+import Data.Word (Word16)
 import qualified Data.IntMap as IntMap
 import qualified Data.Text.Encoding as Text
 import qualified Data.Text.Lazy as Text.Lazy
 import qualified Data.Text.Lazy.Builder as Text.Builder
 import qualified Data.Text.Lazy.Builder.Int as Text.Builder
+import Data.Vector (Vector)
 import qualified Data.Vector as Vector
 import Data.Void
 import GHC.Records (HasField(..))
@@ -42,6 +44,7 @@ import Graphics.Fountainhead.Parser
     , cmapTableP
     )
 import Data.Foldable (Foldable(..))
+import Data.Maybe (fromMaybe)
 
 type ParseErrorOrDump
     = Either (Megaparsec.ParseErrorBundle ByteString Void) Text.Builder.Builder
@@ -128,6 +131,7 @@ dumpCmap CmapTable{..}
         (CmapFormat2 _) -> "Format 2"
         (CmapFormat4 CmapFormat4Table{..}) ->
             let segCount = Vector.length startCode
+                dumpSegment' = dumpSegment segCount glyphIndexArray
              in "Format 4 - Segment mapping to delta values\n\
                 \                 Length:     994\n\
                 \                 Version:      0\n\
@@ -140,14 +144,32 @@ dumpCmap CmapTable{..}
                 <> newlineBuilder <> "                 rangeShift:     "
                 <> Text.Builder.decimal (segCount * 2 - fromIntegral searchRange)
                 <> newlineBuilder
-                <> fold (Vector.izipWith4 (dumpSegment segCount) startCode endCode idDelta idRangeOffset)
+                <> fold (Vector.izipWith4 (dumpSegmentSummary segCount) startCode endCode idDelta idRangeOffset)
+                <> "                 Number of glyphIndex "
+                <> Text.Builder.decimal (Vector.length glyphIndexArray) <> newlineBuilder
+                <> fold (Vector.imap dumpGlyphAtIndex glyphIndexArray)
+                <> fold (Vector.izipWith4 dumpSegment' startCode endCode idDelta idRangeOffset)
         (CmapFormat6 _) -> "Format 6"
         (CmapFormat8 _) -> "Format 8"
         (CmapFormat10 _) -> "Format 10"
         (CmapFormat12 _) -> "Format 12"
         (CmapFormat13 _) -> "Format 13"
         (CmapFormat14 _) -> "Format 14"
-    dumpSegment segCount index startCode' endCode' idDelta' idRangeOffset'
+    dumpSegment :: Int -> Vector Word16 -> Int -> Word16 -> Word16 -> Word16 -> Word16 -> Text.Builder.Builder
+    dumpSegment segCount glyphIndexArray' segmentIndex startCode' endCode' idDelta' idRangeOffset' =
+        let charRange = [startCode'..endCode']
+            dumpSegmentCharIndex' =
+                dumpSegmentCharIndex segCount glyphIndexArray' segmentIndex idDelta' idRangeOffset' startCode'
+         in "Segment " <> Text.Builder.decimal segmentIndex <> ":\n"
+            <> foldMap dumpSegmentCharIndex' charRange
+    dumpSegmentCharIndex segCount glyphIndexArray' segmentIndex idDelta' idRangeOffset' startCode' charCode =
+        let calculateGlyphIndex' =
+                calculateGlyphIndex charCode segmentIndex segCount glyphIndexArray' idRangeOffset' idDelta' startCode'
+         in "                 Char 0x"
+            <> halfPaddedHexadecimal charCode <> " -> Index "
+            <> Text.Builder.decimal calculateGlyphIndex'
+            <> newlineBuilder
+    dumpSegmentSummary segCount index startCode' endCode' idDelta' idRangeOffset'
         = "                 Seg " <> justifyNumber 5 index
         <> " : St = " <> halfPaddedHexadecimal startCode'
         <> ", En = " <> halfPaddedHexadecimal endCode'
@@ -155,9 +177,23 @@ dumpCmap CmapTable{..}
         <> ", RO = " <> justifyNumber 6 idRangeOffset'
         <> ", gId# = " <> dumpGlyphId index segCount idRangeOffset'
         <> newlineBuilder
-    dumpGlyphId index segCount idRangeOffset'
-        | idRangeOffset' == 0 = "N/A"
-        | otherwise = Text.Builder.decimal $ index - segCount + (fromIntegral idRangeOffset' `div` 2)
+    dumpGlyphId segmentIndex segCount idRangeOffset'
+        = maybe "N/A" Text.Builder.decimal
+        $ calculateGlyphId segmentIndex segCount idRangeOffset'
+    calculateGlyphIndex :: Word16 -> Int -> Int -> Vector Word16 -> Word16 -> Word16 -> Word16 -> Int
+    calculateGlyphIndex c segmentIndex segCount glyphIndexArray' idRangeOffset' idDelta' startCode' =
+        let defaultIndex = fromIntegral $ c + idDelta'
+            addOffset = fromIntegral
+                . fromMaybe 0
+                . (glyphIndexArray' Vector.!?)
+                . (+ fromIntegral (c - startCode'))
+         in maybe defaultIndex addOffset
+            $ calculateGlyphId segmentIndex segCount idRangeOffset'
+    calculateGlyphId segmentIndex segCount idRangeOffset'
+        | idRangeOffset' == 0 = Nothing
+        | otherwise = Just $ segmentIndex - segCount + (fromIntegral idRangeOffset' `div` 2)
+    dumpGlyphAtIndex index element = "                 glyphIdArray[" <> Text.Builder.decimal index <> "] =  "
+        <> Text.Builder.decimal element <> newlineBuilder
 
 dumpTables
     :: Megaparsec.State ByteString Void