https://gitlab.com/menelkir/libg15render/-/commit/ea940d38ca5c17685e4c13dcdcde43bbd6ec1fea
--- a/pixel.c
+++ b/pixel.c
@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <stdlib.h>
 #include <math.h>
+#include <unistd.h>
 #include "libg15render.h"
 
 void swap (int *x, int *y){