add a sniffer for the XWD format (#4613)

jcupitt · web-flow · commit 00d6076cf62b · 2025-07-19T15:05:46.000+01:00
otherwise we mistake it for TGA see #4612
diff --git a/libvips/foreign/magick.c b/libvips/foreign/magick.c
@@ -138,6 +138,15 @@ magick_sniff(const unsigned char *bytes, size_t length)
 		(bytes[4] != 0 || bytes[5] != 0))
 		return "ICO";
 
+	if (length >= 8 &&
+		bytes[1] == 0 &&
+		bytes[2] == 0 &&
+		bytes[5] == 0 &&
+		bytes[6] == 0 &&
+		(bytes[4] == 7 ||
+		 bytes[7] == 7))
+		return "XWD";
+
 	if (length >= 18 &&
 		(bytes[1] == 0 ||
 			bytes[1] == 1) &&
