dwebp: move webp decoding to example_util

this will allow reuse by cwebp

Change-Id: I667252fdacfc5436112d21b040ca299273ec1515

examples/example_util.h

@@ -19,6 +19,9 @@
 extern "C" {
 #endif
 
+struct WebPDecoderConfig;
+struct WebPBitstreamFeatures;
+
 // Allocates storage for entire file 'file_name' and returns contents and size
 // in 'data' and 'data_size'. Returns 1 on success, 0 otherwise. '*data' should
 // be deleted using free().
@@ -35,6 +38,32 @@ int ExUtilReadFromStdin(const uint8_t** data, size_t* data_size);
 int ExUtilWriteFile(const char* const file_name,
                     const uint8_t* data, size_t data_size);
 
+//------------------------------------------------------------------------------
+// WebP decoding
+
+// Prints an informative error message regarding decode failure of 'in_file'.
+// 'status' is treated as a VP8StatusCode and if valid will be printed as a
+// text string.
+void ExUtilPrintWebPError(const char* const in_file, int status);
+
+// Reads a WebP from 'in_file', returning the contents and size in 'data' and
+// 'data_size'. 'bitstream' is populated using WebPGetFeatures().
+// Returns true on success.
+int ExUtilLoadWebP(const char* const in_file,
+                   const uint8_t** data, size_t* data_size,
+                   struct WebPBitstreamFeatures* bitstream);
+
+// Decodes the WebP contained in 'data'. 'config' is a structure previously
+// initialized by WebPInitDecoderConfig(). 'config->output' should have the
+// desired colorspace selected. If 'incremental' is set to true the WebP
+// incremental decoder will be used. 'verbose' will cause decode timing to be
+// reported.
+// Returns the decoder status. On success 'config->output' will contain the
+// decoded picture.
+enum VP8StatusCode ExUtilDecodeWebP(const uint8_t* const data, size_t data_size,
+                                    int incremental, int verbose,
+                                    struct WebPDecoderConfig* const config);
+
 #ifdef __cplusplus
 }    // extern "C"
 #endif