From 4708393c3b647480046d72d42e7b67eef768dee2 Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Thu, 21 Jun 2012 18:27:54 -0700
Subject: [PATCH] demux: add {Next,Prev}Chunk

replaces WebPDemuxSetChunk(). makes this consistent with the Frame
interface.

Change-Id: Ia2b1b98cc290f35b41fd14ee35a2a17cecac7ba8
---
 src/mux/demux.c | 16 +++++++++++++---
 src/webp/mux.h  |  7 ++++---
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/mux/demux.c b/src/mux/demux.c
index 2b4caf2f..d219ddfe 100644
--- a/src/mux/demux.c
+++ b/src/mux/demux.c
@@ -853,10 +853,20 @@ int WebPDemuxGetChunk(const WebPDemuxer* const dmux,
   return SetChunk(fourcc, chunk_num, iter);
 }
 
-int WebPDemuxSetChunk(WebPChunkIterator* const iter, int chunk) {
+int WebPDemuxNextChunk(WebPChunkIterator* const iter) {
   if (iter != NULL) {
-    const uint8_t* const header = iter->chunk_.bytes_ - CHUNK_HEADER_SIZE;
-    return SetChunk((const char*)header, chunk, iter);
+    const char* const fourcc =
+        (const char*)iter->chunk_.bytes_ - CHUNK_HEADER_SIZE;
+    return SetChunk(fourcc, iter->chunk_num_ + 1, iter);
+  }
+  return 0;
+}
+
+int WebPDemuxPrevChunk(WebPChunkIterator* const iter) {
+  if (iter != NULL && iter->chunk_num_ > 1) {
+    const char* const fourcc =
+        (const char*)iter->chunk_.bytes_ - CHUNK_HEADER_SIZE;
+    return SetChunk(fourcc, iter->chunk_num_ - 1, iter);
   }
   return 0;
 }
diff --git a/src/webp/mux.h b/src/webp/mux.h
index ee3a7d4a..c86fd5a9 100644
--- a/src/webp/mux.h
+++ b/src/webp/mux.h
@@ -585,10 +585,11 @@ WEBP_EXTERN(int) WebPDemuxGetChunk(const WebPDemuxer* const dmux,
                                    const char fourcc[4], int chunk_number,
                                    WebPChunkIterator* const iter);
 
-// Sets 'iter->chunk_' to point to chunk 'chunk_number'.
+// Sets 'iter->chunk_' to point to the next ('iter->chunk_num_' + 1) or previous
+// ('iter->chunk_num_' - 1) chunk. These functions do not loop.
 // Returns true on success, false otherwise.
-WEBP_EXTERN(int) WebPDemuxSetChunk(WebPChunkIterator* const iter,
-                                   int chunk_number);
+WEBP_EXTERN(int) WebPDemuxNextChunk(WebPChunkIterator* const iter);
+WEBP_EXTERN(int) WebPDemuxPrevChunk(WebPChunkIterator* const iter);
 
 // Releases any memory associated with 'iter'.
 // Must be called before destroying the associated WebPDemuxer with