WMF/EMF: Unpack signed integers using unpack()

PIL/WmfImagePlugin.py

@@ -14,6 +14,10 @@
 #
 # See the README file for information on usage and redistribution.
 #
+# WMF/EMF reference documentation:
+# https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-WMF/[MS-WMF].pdf
+# http://wvware.sourceforge.net/caolan/index.html
+# http://wvware.sourceforge.net/caolan/ora-wmf.html
 
 from PIL import Image, ImageFile, _binary
 
@@ -56,21 +60,9 @@ if hasattr(Image.core, "drawwmf"):
 # --------------------------------------------------------------------
 
 word = _binary.i16le
-
+short = _binary.si16le
-
-def short(c, o=0):
-    v = word(c, o)
-    if v >= 32768:
-        v -= 65536
-    return v
-
 dword = _binary.i32le
-
+_long = _binary.si32le
-def _long(c, o=0):
-    v = dword(c, o)
-    if v >= 1<<31:
-        v -= 1<<32
-    return v
 
 #
 # --------------------------------------------------------------------
@@ -132,7 +124,7 @@ class WmfStubImageFile(ImageFile.StubImageFile):
             y1 = _long(s, 20)
 
             # get frame (in 0.01 millimeter units)
-            frame = dword(s, 24), dword(s, 28), dword(s, 32), dword(s, 36)
+            frame = _long(s, 24), _long(s, 28), _long(s, 32), _long(s, 36)
 
             # normalize size to 72 dots per inch
             size = x1 - x0, y1 - y0

PIL/_binary.py

@@ -31,23 +31,41 @@ else:
 # TODO: replace with more readable struct.unpack equivalent
 def i16le(c, o=0):
     """
-    Converts a 2-bytes (16 bits) string to an integer.
+    Converts a 2-bytes (16 bits) string to an unsigned integer.
 
     c: string containing bytes to convert
     o: offset of bytes to convert in string
     """
     return unpack("<H", c[o:o+2])[0]
 
+def si16le(c, o=0):
+    """
+    Converts a 2-bytes (16 bits) string to a signed integer.
+
+    c: string containing bytes to convert
+    o: offset of bytes to convert in string
+    """
+    return unpack("<h", c[o:o+2])[0]
+
 
 def i32le(c, o=0):
     """
-    Converts a 4-bytes (32 bits) string to an integer.
+    Converts a 4-bytes (32 bits) string to an unsigned integer.
 
     c: string containing bytes to convert
     o: offset of bytes to convert in string
     """
     return unpack("<I", c[o:o+4])[0]
 
+def si32le(c, o=0):
+    """
+    Converts a 4-bytes (32 bits) string to a signed integer.
+
+    c: string containing bytes to convert
+    o: offset of bytes to convert in string
+    """
+    return unpack("<i", c[o:o+4])[0]
+
 
 def i16be(c, o=0):
     return unpack(">H", c[o:o+2])[0]

Tests/test_file_wmf.py

@@ -6,11 +6,25 @@ class TestFileWmf(PillowTestCase):
 
     def test_load_raw(self):
 
-        # Test basic EMF open
+        # Test basic EMF open and rendering
         im = Image.open('Tests/images/drawing.emf')
+        if hasattr(Image.core, "drawwmf"):
+            # Currently, support for WMF/EMF is Windows-only
+            im.load()
+            # Compare to reference rendering
+            imref = Image.open('Tests/images/drawing_emf_ref.png')
+            imref.load()
+            self.assert_image_equal(im, imref)
 
-        # Test basic WMF open
+        # Test basic WMF open and rendering
         im = Image.open('Tests/images/drawing.wmf')
+        if hasattr(Image.core, "drawwmf"):
+            # Currently, support for WMF/EMF is Windows-only
+            im.load()
+            # Compare to reference rendering
+            imref = Image.open('Tests/images/drawing_wmf_ref.png')
+            imref.load()
+            self.assert_image_equal(im, imref)
 
 
 if __name__ == '__main__':