From a34a502989463aee1f08f1bd17733264df99f813 Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Tue, 9 Jul 2013 17:33:21 -0700
Subject: [PATCH] pngdec: output error messages from libpng

Change-Id: I1981562eeab2ad07eb797cea589a033943e7f21d
---
 examples/pngdec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/examples/pngdec.c b/examples/pngdec.c
index 59e8b77d..332f6bbd 100644
--- a/examples/pngdec.c
+++ b/examples/pngdec.c
@@ -26,8 +26,8 @@
 #include "webp/encode.h"
 #include "./metadata.h"
 
-static void PNGAPI error_function(png_structp png, png_const_charp dummy) {
-  (void)dummy;  // remove variable-unused warning
+static void PNGAPI error_function(png_structp png, png_const_charp error) {
+  if (error != NULL) fprintf(stderr, "libpng error: %s\n", error);
   longjmp(png_jmpbuf(png), 1);
 }