demo: refuse to write image to terminal

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 6 insertions, 0 deletions

diff --git a/demo.c b/demo.c
index dbc20c7..063721c 100644
--- a/demo.c
+++ b/demo.c
@@ -3,6 +3,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 int
 main(void)
@@ -15,6 +16,11 @@ main(void)
 	double height;
 	size_t size, i;
 
+	if (isatty(STDOUT_FILENO)) {
+		fprintf(stderr, "Output file is a binary PAM image file, I am not writing that to a terminal.\n");
+		return 1;
+	}
+
 	rendering.smoothing           = LIBSKRIFT_SUBPIXEL;
 	rendering.subpixel_order      = LIBSKRIFT_NONE;
 	rendering.flags               = LIBSKRIFT_MIRROR_CHARS | LIBSKRIFT_MIRROR_TEXT;