image_dec: add WebPGetEnabledInputFileFormats()

and use it to output the types supported in the examples

Change-Id: Ia6b8624a2146cf72c679129065a72f215644e1e9

examples/cwebp.c

@@ -620,6 +620,7 @@ static void HelpLong(void) {
   printf("  -af .................... auto-adjust filter strength\n");
   printf("  -pre <int> ............. pre-processing filter\n");
   printf("\n");
+  printf("Supported input formats:\n  %s\n", WebPGetEnabledInputFileFormats());
 }
 
 //------------------------------------------------------------------------------

examples/img2webp.c

@@ -65,6 +65,8 @@ static void Help(void) {
          "arguments will be\n");
   printf("tokenized from this file. The file name must not start with "
          "the character '-'.\n");
+  printf("\nSupported input formats:\n  %s\n",
+         WebPGetEnabledInputFileFormats());
 }
 
 //------------------------------------------------------------------------------
@@ -186,7 +188,7 @@ int main(int argc, const char* argv[]) {
         verbose = 1;
       } else if (!strcmp(argv[c], "-h") || !strcmp(argv[c], "-help")) {
         Help();
-        goto End;
+        FREE_WARGV_AND_RETURN(0);
       } else if (!strcmp(argv[c], "-version")) {
         const int enc_version = WebPGetEncoderVersion();
         const int mux_version = WebPGetMuxVersion();

extras/get_disto.c

@@ -223,7 +223,8 @@ static void Help(void) {
           "  -o <file> . save the diff map as a WebP lossless file\n"
           "  -scale .... scale the difference map to fit [0..255] range\n"
           "  -gray ..... use grayscale for difference map (-scale)\n"
-          " Also handles PNG, JPG and TIFF files, in addition to WebP.\n");
+          "\nSupported input formats:\n  %s\n",
+          WebPGetEnabledInputFileFormats());
 }
 
 int main(int argc, const char* argv[]) {

imageio/image_dec.c

@@ -11,6 +11,24 @@
 
 #include "./image_dec.h"
 
+const char* WebPGetEnabledInputFileFormats(void) {
+  return "WebP"
+#ifdef WEBP_HAVE_JPEG
+         ", JPEG"
+#endif
+#ifdef WEBP_HAVE_PNG
+         ", PNG"
+#endif
+         ", PNM (PGM, PPM, PAM)"
+#ifdef WEBP_HAVE_TIFF
+         ", TIFF"
+#endif
+#ifdef HAVE_WINCODEC_H
+         ", Windows Imaging Component (WIC)"
+#endif
+         "";
+}
+
 static WEBP_INLINE uint32_t GetBE32(const uint8_t buf[]) {
   return ((uint32_t)buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];
 }

imageio/image_dec.h

@@ -41,6 +41,9 @@ typedef enum {
   WEBP_UNSUPPORTED_FORMAT
 } WebPInputFileFormat;
 
+// Returns a comma separated list of enabled input formats.
+const char* WebPGetEnabledInputFileFormats(void);
+
 // Try to infer the image format. 'data_size' should be larger than 12.
 // Returns WEBP_UNSUPPORTED_FORMAT if format can't be guess safely.
 WebPInputFileFormat WebPGuessImageType(const uint8_t* const data,