From 585d0bde25764ac774eaa5d309d8e887d4fef22b Mon Sep 17 00:00:00 2001
From: David Baer <david@amyanddavid.net>
Date: Wed, 21 Apr 2021 22:22:57 -0400
Subject: [PATCH] Allow piping image to stdout

---
 src/image.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/image.c b/src/image.c
index b2a3ff6..b6eac9e 100644
--- a/src/image.c
+++ b/src/image.c
@@ -93,11 +93,15 @@ int writePNG(mazegrid_t const* g, char const* filename) {
     png_structp png_ptr = NULL;
     png_infop info_ptr  = NULL;
     
-    f = fopen(filename, "wb");
-    if (NULL == f) {
-        fprintf(stderr, "Could not open %s for writing.\n", filename);
-        code = 0;
-        goto exit;
+    if (strcmp(filename, "-") == 0) {
+        f = stdout;
+    } else {
+        f = fopen(filename, "wb");
+        if (NULL == f) {
+            fprintf(stderr, "Could not open %s for writing.\n", filename);
+            code = 0;
+            goto exit;
+        }
     }
 
     png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
@@ -134,7 +138,9 @@ int writePNG(mazegrid_t const* g, char const* filename) {
     png_write_end(png_ptr, NULL);
 
 exit:
-    if (f != NULL) fclose(f);
+    if (strcmp(filename, "-") != 0) {
+        if (f != NULL) fclose(f);
+    }
 	if (info_ptr != NULL) {
         png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);
         png_destroy_info_struct(png_ptr, &info_ptr);