From 542ec7c7a5e756e8a3463fd41ee18db37c6b4e4f Mon Sep 17 00:00:00 2001
From: Robin Stuart <rstuart114@gmail.com>
Date: Fri, 26 Aug 2016 11:44:02 +0100
Subject: [PATCH] When libpng is not found, default to GIF output

---
 backend/CMakeLists.txt | 4 +++-
 backend/library.c      | 9 +++++++++
 backend/raster.c       | 1 -
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/backend/CMakeLists.txt b/backend/CMakeLists.txt
index ba149d15..3dd8d073 100644
--- a/backend/CMakeLists.txt
+++ b/backend/CMakeLists.txt
@@ -22,7 +22,9 @@ add_library(zint SHARED ${zint_SRCS})
 set_target_properties(zint PROPERTIES 	SOVERSION "${ZINT_VERSION_MAJOR}.${ZINT_VERSION_MINOR}"
 					VERSION ${ZINT_VERSION})
 
-target_link_libraries(zint ${PNG_LIBRARIES} )
+if(PNG_FOUND)
+    target_link_libraries(zint ${PNG_LIBRARIES} )
+endif(PNG_FOUND)
 target_link_libraries(zint -lm)
 
 install(TARGETS zint  ${INSTALL_TARGETS_DEFAULT_ARGS} )
diff --git a/backend/library.c b/backend/library.c
index ec044180..62d594e0 100644
--- a/backend/library.c
+++ b/backend/library.c
@@ -781,7 +781,11 @@ int ZBarcode_Encode(struct zint_symbol *symbol, unsigned char *source, int lengt
     }
 
     if (strcmp(symbol->outfile, "") == 0) {
+#ifdef NO_PNG
+        strcpy(symbol->outfile, "out.gif");
+#else    
         strcpy(symbol->outfile, "out.png");
+#endif
     }
 #ifndef _MSC_VER
     unsigned char local_source[length + 1];
@@ -1085,6 +1089,11 @@ int ZBarcode_Print(struct zint_symbol *symbol, int rotate_angle) {
         return ZINT_ERROR_INVALID_OPTION;
     }
 
+    if (error_number == ZINT_ERROR_INVALID_OPTION) {
+        /* If libpng is not installed */
+        strcpy(symbol->errtxt, "Unknown output format");
+    }
+    
     error_tag(symbol->errtxt, error_number);
     return error_number;
 }
diff --git a/backend/raster.c b/backend/raster.c
index 51f7b829..d13c1c5a 100644
--- a/backend/raster.c
+++ b/backend/raster.c
@@ -927,7 +927,6 @@ int plot_raster(struct zint_symbol *symbol, int rotate_angle, int file_type) {
 
 #ifdef NO_PNG
     if (file_type == OUT_PNG_FILE) {
-        printf("libpng not found");
         return ZINT_ERROR_INVALID_OPTION;
     }
 #endif /* NO_PNG */