Date: Mon, 10 Apr 2006 08:29:17 -0400

From: Stea Greene Subject: [SDL] Patch for JPEG Loading in SDL_image This fixes the JPEG detection routine in SDL_image such that it should be able to detect any JPEG file, JFIF or not. It does this by parsing the headers and tags, rather than expecting specific ones in order with no gaps. This also enables it to load raw 32-bit JPEG files, with an alpha channel. While not defined specifically in the JPEG spec (as far as I know), this is the format used internally by the .blp files in some of Blizzard's recent titles. It detects this from the JPEG itself, and should not cause any problems with any normal JPEGs that were loadable previously (in fact, it should make more of them loadable). I've tested it on both little and big endian and on just about every kind of file I can find. So far, it has worked perfectly in every case. I've also tested it with a number of .blp files and it works great. Note that .blp is NOT really an image format, so this won't load them straight up. You have to process them a bit before you can load them as JPEGs. Once you do that (and it's trivial), this patch makes SDL_image load them fine.
libsdl-org · Apr 20, 2006 · ccb4bb7 · ccb4bb7
1 parent 297ed08
commit ccb4bb7
Showing 1 changed file with 79 additions and 26 deletions.
diff --git a/IMG_jpg.c b/IMG_jpg.c
@@ -35,29 +35,65 @@
 /* Define this for fast loading and not as good image quality */
 /*#define FAST_JPEG*/
 
+/* Define this for quicker (but less perfect) JPEG identification */
+#define FAST_IS_JPEG
+
 /* See if an image is contained in a data source */
 int IMG_isJPG(SDL_RWops *src)
 {
 	int start;
 	int is_JPG;
+	int in_scan;
 	Uint8 magic[4];
 
+	/* This detection code is by Steaphan Greene <stea@cs.binghamton.edu> */
+	/* Blame me, not Sam, if this doesn't work right. */
+	/* And don't forget to report the problem to the the sdl list too! */
+
 	start = SDL_RWtell(src);
 	is_JPG = 0;
+	in_scan = 0;
 	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 ||
-			     memcmp((char *)magic, "VVL", 3) == 0 ) {
-				is_JPG = 1;
+			is_JPG = 1;
+			while (is_JPG == 1) {
+				if(SDL_RWread(src, magic, 1, 2) != 2) {
+					is_JPG = 0;
+				} else if( (magic[0] != 0xFF) && (in_scan == 0) ) {
+					is_JPG = 0;
+				} else if( (magic[0] != 0xFF) || (magic[1] == 0xFF) ) {
+					/* Extra padding in JPEG (legal) */
+					/* or this is data and we are scanning */
+					SDL_RWseek(src, -1, SEEK_CUR);
+				} else if(magic[1] == 0xD9) {
+					/* Got to end of good JPEG */
+					break;
+				} else if( (in_scan == 1) && (magic[1] == 0x00) ) {
+					/* This is an encoded 0xFF within the data */
+				} else if( (magic[1] >= 0xD0) && (magic[1] < 0xD9) ) {
+					/* These have nothing else */
+				} else if(SDL_RWread(src, magic+2, 1, 2) != 2) {
+					is_JPG = 0;
+				} else {
+					/* Yes, it's big-endian */
+					Uint32 start;
+					Uint32 size;
+					Uint32 end;
+					start = SDL_RWtell(src);
+					size = (magic[2] << 8) + magic[3];
+					end = SDL_RWseek(src, size-2, SEEK_CUR);
+					if ( end != start + size - 2 ) is_JPG = 0;
+					if ( magic[1] == 0xDA ) {
+						/* Now comes the actual JPEG meat */
+#ifdef	FAST_IS_JPEG
+						/* Ok, I'm convinced.  It is a JPEG. */
+						break;
+#else
+						/* I'm not convinced.  Prove it! */
+						in_scan = 1;
+#endif
+					}
+				}
 			}
 		}
 	}
@@ -231,26 +267,43 @@ SDL_Surface *IMG_LoadJPG_RW(SDL_RWops *src)
 	jpeg_SDL_RW_src(&cinfo, src);
 	jpeg_read_header(&cinfo, TRUE);
 
-	/* Set 24-bit RGB output */
-	cinfo.out_color_space = JCS_RGB;
-	cinfo.quantize_colors = FALSE;
+	if(cinfo.num_components == 4) {
+		/* Set 32-bit Raw output */
+		cinfo.out_color_space = JCS_CMYK;
+		cinfo.quantize_colors = FALSE;
+		jpeg_calc_output_dimensions(&cinfo);
+
+		/* Allocate an output surface to hold the image */
+		surface = SDL_AllocSurface(SDL_SWSURFACE,
+		        cinfo.output_width, cinfo.output_height, 32,
+#if SDL_BYTEORDER == SDL_LIL_ENDIAN
+		                   0x00FF0000, 0x0000FF00, 0x000000FF, 0xFF000000);
+#else
+		                   0x0000FF00, 0x00FF0000, 0xFF000000, 0x000000FF);
+#endif
+	} else {
+		/* Set 24-bit RGB output */
+		cinfo.out_color_space = JCS_RGB;
+		cinfo.quantize_colors = FALSE;
 #ifdef FAST_JPEG
-	cinfo.scale_num   = 1;
-	cinfo.scale_denom = 1;
-	cinfo.dct_method = JDCT_FASTEST;
-	cinfo.do_fancy_upsampling = FALSE;
+		cinfo.scale_num   = 1;
+		cinfo.scale_denom = 1;
+		cinfo.dct_method = JDCT_FASTEST;
+		cinfo.do_fancy_upsampling = FALSE;
 #endif
-	jpeg_calc_output_dimensions(&cinfo);
+		jpeg_calc_output_dimensions(&cinfo);
 
-	/* Allocate an output surface to hold the image */
-	surface = SDL_AllocSurface(SDL_SWSURFACE,
-	               cinfo.output_width, cinfo.output_height, 24,
+		/* Allocate an output surface to hold the image */
+		surface = SDL_AllocSurface(SDL_SWSURFACE,
+		        cinfo.output_width, cinfo.output_height, 24,
 #if SDL_BYTEORDER == SDL_LIL_ENDIAN
-	                           0x0000FF, 0x00FF00, 0xFF0000,
+		                   0x0000FF, 0x00FF00, 0xFF0000,
 #else
-	                           0xFF0000, 0x00FF00, 0x0000FF,
+		                   0xFF0000, 0x00FF00, 0x0000FF,
 #endif
-				   0);
+		                   0);
+	}
+
 	if ( surface == NULL ) {
 		jpeg_destroy_decompress(&cinfo);
 		SDL_RWseek(src, start, SEEK_SET);