SDL_image jpeg IPTC patch.

--ryan. Date: Mon, 15 Aug 2005 21:24:39 -0700 (PDT) From: Jeremy Stanley <stanmuffin@yahoo.com> To: sdl@libsdl.org Subject: [SDL] SDL_Image: IMG_isJPG() fails on pictures with IPTC information I found that SDL_Image fails to load JPEG files to which I have added a caption using Picasa (a free as in beer picture organization tool; http://www.picasa.com). Picasa claims to store its captions in IPTC format. Photoshop apparently uses this format too, but I don't have that program so I can't verify that. The problem is that the IPTC information block is stored between the SOI (FF D8) and APP1 (FF E1) markers in the JPEG file, so that the "JFIF" or "Exif" constant is not stored at offset 6. Instead, the two bytes at offset 2 store FF ED and the next two bytes store the size of the block as a big endian word (including the size field). The APP1 (FF E1) marker will immediately follow. A simple fix could be inserted just after the second SDL_RWread() in IMG_isJPG(). Instead of throwing these four bytes away, we can check for the IPTC header and skip over it. The following code does the trick for me.
libsdl-org · Sep 8, 2005 · 5e3c1d4 · 5e3c1d4
1 parent 2c74770
commit 5e3c1d4
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/IMG_jpg.c b/IMG_jpg.c
@@ -47,6 +47,12 @@ int IMG_isJPG(SDL_RWops *src)
 	if ( SDL_RWread(src, magic, 2, 1) ) {
 		if ( (magic[0] == 0xFF) && (magic[1] == 0xD8) ) {
 			SDL_RWread(src, magic, 4, 1);
+
+			/* skip IPTC info block if it exists... */
+			if ( (magic[0] == 0xFF) && (magic[1] == 0xED) ) {
+				SDL_RWseek(src, (((Uint16)magic[2] << 8) |magic[3]) + 2, SEEK_CUR);
+			}
+
 			SDL_RWread(src, magic, 4, 1);
 			if ( memcmp((char *)magic, "JFIF", 4) == 0 ||
 			     memcmp((char *)magic, "Exif", 4) == 0 ||