fix(docx): use proper DPI for svg to fallback png conversions

DPI only works when the desired size is known, otherwise rsvg-convert
will use the SVG's viewbox to guess the size in pixels.
That size is often very small, resulting in a very bad quality fallback
PNG.

Signed-off-by: Edwin Török <edwin@etorok.net>

src/Text/Pandoc/App.hs

@@ -49,7 +49,7 @@ import System.IO (nativeNewline, stdout)
 import qualified System.IO as IO (Newline (..))
 import Text.Pandoc
 import Text.Pandoc.Builder (setMeta)
-import Text.Pandoc.MediaBag (mediaItems)
+import Text.Pandoc.MediaBag (mediaItems')
 import Text.Pandoc.Image (svgToPng)
 import Text.Pandoc.App.Opt (Opt (..), LineEnding (..), defaultOpts,
                             IpynbOutput (..), OptInfo(..))
@@ -73,6 +73,7 @@ import qualified Text.Pandoc.UTF8 as UTF8
 #ifndef _WINDOWS
 import System.Posix.IO (stdOutput)
 import System.Posix.Terminal (queryTerminal)
+import Text.Pandoc.ImageSize (desiredSizeInPoints, imageSize)
 #endif
 
 convertWithOpts :: ScriptingEngine -> Opt -> IO ()
@@ -308,7 +309,7 @@ convertWithOpts' scriptingEngine istty datadir opts = do
             )
 
   when (format == "docx" && not (optSandbox opts)) $ do
-    createPngFallbacks (writerDpi writerOptions)
+    createPngFallbacks writerOptions
 
   output <- case writer of
     ByteStringWriter f
@@ -372,14 +373,15 @@ readAbbreviations mbfilepath =
     >>= fmap (Set.fromList . filter (not . T.null) . T.lines) .
          toTextM (fromMaybe mempty mbfilepath)
 
-createPngFallbacks :: (PandocMonad m, MonadIO m) => Int -> m ()
-createPngFallbacks dpi = do
+createPngFallbacks :: (PandocMonad m, MonadIO m) => WriterOptions -> m ()
+createPngFallbacks opts = do
   -- create fallback pngs for svgs
-  items <- mediaItems <$> getMediaBag
-  forM_ items $ \(fp, mt, bs) ->
+  items <- mediaItems' <$> getMediaBag
+  forM_ items $ \(fp, mt, bs, attr) ->
     case T.takeWhile (/=';') mt of
       "image/svg+xml" -> do
-        res <- svgToPng dpi bs
+        let dims = either (const Nothing) (Just . desiredSizeInPoints opts attr) (imageSize opts $ BL.toStrict bs)
+        res <- svgToPng dims (writerDpi opts) bs
         case res of
           Right bs' -> do
             let fp' = fp <> ".png"

src/Text/Pandoc/Image.hs

@@ -20,16 +20,21 @@ import qualified Control.Exception as E
 import Control.Monad.IO.Class (MonadIO(liftIO))
 import Text.Pandoc.Class.PandocMonad
 import qualified Data.Text as T
+import Text.Printf (printf)
 
 -- | Convert svg image to png. rsvg-convert
 -- is used and must be available on the path.
 svgToPng :: (PandocMonad m, MonadIO m)
-         => Int           -- ^ DPI
+         => Maybe (Double, Double) -- Width and Height in points
+         -> Int           -- ^ DPI
          -> L.ByteString  -- ^ Input image as bytestring
          -> m (Either Text L.ByteString)
-svgToPng dpi bs = do
+svgToPng dims dpi bs = do
   let dpi' = show dpi
   let args = ["-f","png","-a","--dpi-x",dpi',"--dpi-y",dpi']
+         ++ maybe [] (\(xpt, ypt) ->
+                           ["--width", printf "%.6fpt" xpt, "--height", printf "%.6fpt" ypt])
+                  dims
   trace (T.intercalate " " $ map T.pack $ "rsvg-convert" : args)
   liftIO $ E.catch
        (do (exit, out) <- pipeProcess Nothing "rsvg-convert"