Flip and rotate images in LaTeX output

Ordinarily the LaTeX writer doesn't really need to get the bytes of the
images it's including, but we have to check them to get an EXIF
orientation. If the media fetch fails we're just punting and assuming a
default orientation.

It would be slightly dubious to bother doing this at all but LaTeX is
the default format for PDF output so it's worth making the effort.

src/Text/Pandoc/ImageSize.hs

@@ -27,6 +27,7 @@ module Text.Pandoc.ImageSize ( ImageType(..)
                              , Flip(..)
                              , Rotate(..)
                              , dimension
+                             , rotateDirection
                              , lengthToDim
                              , scaleDimension
                              , inInch
@@ -515,3 +516,11 @@ imageTransform img =
     exifToTransform 7 = def{tFlip = FlipH, tRotate = R90}
     exifToTransform 8 = def{tRotate = R270}
     exifToTransform _ = def
+
+rotateDirection :: Rotate -> Direction -> Direction
+rotateDirection R0 x = x
+rotateDirection R90 Width = Height
+rotateDirection R90 Height = Width
+rotateDirection R180 x = x
+rotateDirection R270 Width = Height
+rotateDirection R270 Height = Width

src/Text/Pandoc/Writers/LaTeX.hs

@@ -30,6 +30,7 @@ import Control.Monad
       liftM,
       when,
       unless )
+import Control.Monad.Except (catchError)
 import Data.Containers.ListUtils (nubOrd)
 import Data.Char (isDigit)
 import Data.List (intersperse, (\\))
@@ -41,7 +42,7 @@ import qualified Data.Text as T
 import Network.URI (unEscapeString)
 import Text.DocTemplates (FromContext(lookupContext), renderTemplate)
 import Text.Collate.Lang (renderLang, Lang(langLanguage))
-import Text.Pandoc.Class.PandocMonad (PandocMonad, report, toLang)
+import Text.Pandoc.Class.PandocMonad (PandocMonad, report, toLang, fetchItem)
 import Text.Pandoc.Definition
 import Text.Pandoc.Highlighting (formatLaTeXBlock, formatLaTeXInline, highlight,
                                  styleToLaTeX)
@@ -1075,23 +1076,25 @@ inlineToLaTeX (Image attr@(_,_,kvs) _ (source, _)) = do
   modify $ \s -> s{ stGraphics = True
                   , stSVG = stSVG s || isSVG }
   opts <- gets stOptions
-  let showDim dir = let d = text (show dir) <> "="
-                    in case dimension dir attr of
+  (ImageTransform flp rot) <- catchError ((imageTransform . fst) <$> fetchItem source) (\_ -> return def)
+  let redir = rotateDirection rot
+      showDim dir = let d = text (show dir) <> "="
+                    in case dimension (redir dir) attr of
                          Just (Pixel a)   ->
                            [d <> literal (showInInch opts (Pixel a)) <> "in"]
                          Just (Percent a) ->
                            [d <> literal (showFl (a / 100)) <>
-                             case dir of
+                             case (redir dir) of
                                 Width  -> "\\linewidth"
                                 Height -> "\\textheight"
                            ]
                          Just dim         ->
                            [d <> text (show dim)]
                          Nothing          ->
                            case dir of
-                                Width | isJust (dimension Height attr) ->
+                                Width | isJust (dimension (redir Height) attr) ->
                                   [d <> "\\linewidth"]
-                                Height | isJust (dimension Width attr) ->
+                                Height | isJust (dimension (redir Width) attr) ->
                                   [d <> "\\textheight"]
                                 _ -> []
       optList = showDim Width <> showDim Height <>
@@ -1107,14 +1110,30 @@ inlineToLaTeX (Image attr@(_,_,kvs) _ (source, _)) = do
       source' = if isURI source
                    then source
                    else T.pack $ unEscapeString $ T.unpack source
+      -- For images in vertically-mirrored exif orientation, \scalebox{1}[-1]
+      -- will reflect them to below the baseline. It seems like to get the
+      -- final image to be aligned with the baseline again, we have to rotate
+      -- it 180 degrees from the default (baseline) origin and then rotate
+      -- it again about the center so it's facing right side up. In real life
+      -- where there's only 8 possible EXIF orientations, there's never any
+      -- other rotation required for a vertical flip, but I think it would
+      -- still interact correctly if it somehow came up.
+      flipbox NoFlip x = x
+      flipbox FlipH x = "\\scalebox{-1}[1]" <> braces x
+      flipbox FlipV x = "\\rotatebox[origin=c]{180}{\\rotatebox{180}{{\\scalebox{1}[-1]" <> braces x <> "}}}"
+      rotatebox R0 x = x
+      rotatebox R90 x = "\\rotatebox[origin=br]{-90}" <> braces x
+      rotatebox R180 x = "\\rotatebox[origin=c]{180}" <> braces x
+      rotatebox R270 x = "\\rotatebox[origin=bl]{-270}" <> braces x
   source'' <- stringToLaTeX URLString source'
   inHeading <- gets stInHeading
   return $
     (if inHeading then "\\protect" else "") <>
     (case dimension Width attr `mplus` dimension Height attr of
        Just _ -> id
        Nothing -> ("\\pandocbounded" <>) . braces)
-      ((if isSVG then "\\includesvg" else "\\includegraphics") <>
+      ((rotatebox rot . flipbox flp) $
+       (if isSVG then "\\includesvg" else "\\includegraphics") <>
         options <> braces (literal source''))
 inlineToLaTeX (Note contents) = do
   setEmptyLine False