Clarify restrictions on OpenType fonts, namely that they must be derived from TrueType outlines, not PostScript

2 files changed, 16 insertions, 5 deletions

diff --git a/font.go b/font.go
index 102efa5..35f59f1 100644
--- a/font.go
+++ b/font.go
@@ -374,10 +374,13 @@ func makeDefinitionFile(fileStr, tpStr, encodingFileStr string, embed bool, encL
 // gofpdf generates. See the makefont utility in the gofpdf package for a
 // command line interface to this function.
 //
-// fontFileStr is the name of the TrueType (or OpenType based on TrueType,
-// extension .ttf) or binary Type1 file (extension .pfb) from which to generate
-// a definition file. If a Type1 file is specified, a metric file with the same
-// pathname except with the extension .afm must be present.
+// fontFileStr is the name of the TrueType file (extension .ttf), OpenType file
+// (extension .otf) or binary Type1 file (extension .pfb) from which to
+// generate a definition file. If an OpenType file is specified, it must be one
+// that is based on TrueType outlines, not PostScript outlines; this cannot be
+// determined from the file extension alone. If a Type1 file is specified, a
+// metric file with the same pathname except with the extension .afm must be
+// present.
 //
 // encodingFileStr is the name of the encoding file that corresponds to the
 // font.
diff --git a/makefont/makefont.go b/makefont/makefont.go
index d3ea19f..eb2993e 100644
--- a/makefont/makefont.go
+++ b/makefont/makefont.go
@@ -14,7 +14,15 @@ func errPrintf(fmtStr string, args ...interface{}) {
 func showHelp() {
 	errPrintf("Usage: %s [options] font_file [font_file...]\n", os.Args[0])
 	flag.PrintDefaults()
-	errPrintf("Example: %s --embed --enc=../font/cp1252.map --dst=../font calligra.ttf /opt/font/symbol.pfb\n", os.Args[0])
+	fmt.Fprintln(os.Stderr, "\n"+
+		"font_file is the name of the TrueType file (extension .ttf), OpenType file\n"+
+		"(extension .otf) or binary Type1 file (extension .pfb) from which to\n"+
+		"generate a definition file. If an OpenType file is specified, it must be one\n"+
+		"that is based on TrueType outlines, not PostScript outlines; this cannot be\n"+
+		"determined from the file extension alone. If a Type1 file is specified, a\n"+
+		"metric file with the same pathname except with the extension .afm must be\n"+
+		"present.")
+	errPrintf("\nExample: %s --embed --enc=../font/cp1252.map --dst=../font calligra.ttf /opt/font/symbol.pfb\n", os.Args[0])
 }
 
 func tutorialSummary(f *gofpdf.Fpdf, fileStr string) {