add WebPISetIOHooks() to set some custom hooks on the incremental decoder object.

Change-Id: I01e973a1e45e3d60dc11fd284df3cbb938cf0485

src/dec/idec.c

@@ -621,6 +621,23 @@ uint8_t* WebPIDecGetYUV(const WebPIDecoder* const idec, int* last_y,
   return src->u.YUVA.y;
 }
 
+int WebPISetIOHooks(WebPIDecoder* const idec,
+                    VP8IoPutHook put,
+                    VP8IoSetupHook setup,
+                    VP8IoTeardownHook teardown,
+                    void* user_data) {
+  if (!idec || !idec->dec_ || idec->state_ > STATE_HEADER) {
+    return 0;
+  }
+
+  idec->io_.put = put;
+  idec->io_.setup = setup;
+  idec->io_.teardown = teardown;
+  idec->io_.opaque = user_data;
+
+  return 1;
+}
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }    // extern "C"
 #endif

src/webp/decode_vp8.h

@@ -38,6 +38,10 @@ extern "C" {
 
 // Input / Output
 typedef struct VP8Io VP8Io;
+typedef int (*VP8IoPutHook)(const VP8Io* io);
+typedef int (*VP8IoSetupHook)(VP8Io* io);
+typedef void (*VP8IoTeardownHook)(const VP8Io* io);
+
 struct VP8Io {
   // set by VP8GetHeaders()
   int width, height;         // picture dimensions, in pixels (invariable).
@@ -60,14 +64,14 @@ struct VP8Io {
   // in-loop filtering level, e.g.). Should return false in case of error
   // or abort request. The actual size of the area to update is mb_w x mb_h
   // in size, taking cropping into account.
-  int (*put)(const VP8Io* io);
+  VP8IoPutHook put;
 
   // called just before starting to decode the blocks.
   // Should returns 0 in case of error.
-  int (*setup)(VP8Io* io);
+  VP8IoSetupHook setup;
 
   // called just after block decoding is finished (or when an error occurred).
-  void (*teardown)(const VP8Io* io);
+  VP8IoTeardownHook teardown;
 
   // this is a recommendation for the user-side yuv->rgb converter. This flag
   // is set when calling setup() hook and can be overwritten by it. It then
@@ -99,6 +103,15 @@ struct VP8Io {
 // Internal, version-checked, entry point
 int VP8InitIoInternal(VP8Io* const, int);
 
+// Set the custom IO function pointers and user-data. The setter for IO hooks
+// should be called before initiating incremental decoding. Returns true if
+// WebPIdecoder object is successfully modified, false otherwise.
+int WebPISetIOHooks(WebPIDecoder* const idec,
+                    VP8IoPutHook put,
+                    VP8IoSetupHook setup,
+                    VP8IoTeardownHook teardown,
+                    void* user_data);
+
 // Main decoding object. This is an opaque structure.
 typedef struct VP8Decoder VP8Decoder;