font/sfnt: add a comment about contour ordering.
Change-Id: I591c735cc1c3108aa806b0a7be6c54152fe2029e
Reviewed-on: https://go-review.googlesource.com/34174
Reviewed-by: Dave Day <djd@golang.org>
diff --git a/font/sfnt/sfnt_test.go b/font/sfnt/sfnt_test.go
index fe43d32..38f0789 100644
--- a/font/sfnt/sfnt_test.go
+++ b/font/sfnt/sfnt_test.go
@@ -87,8 +87,13 @@
}
// wants' vectors correspond 1-to-1 to what's in the CFFTest.sfd file,
- // although for some unknown reason, FontForge reverses the order somewhere
- // along the way when converting from SFD to OpenType/CFF.
+ // although OpenType/CFF and FontForge's SFD have reversed orders.
+ // https://fontforge.github.io/validation.html says that "All paths must be
+ // drawn in a consistent direction. Clockwise for external paths,
+ // anti-clockwise for internal paths. (Actually PostScript requires the
+ // exact opposite, but FontForge reverses PostScript contours when it loads
+ // them so that everything is consistant internally -- and reverses them
+ // again when it saves them, of course)."
//
// The .notdef glyph isn't explicitly in the SFD file, but for some unknown
// reason, FontForge generates a .notdef glyph in the OpenType/CFF file.
