diff --git a/demo.c b/demo.c
new file mode 100644
index 0000000..078f417
--- /dev/null
+++ b/demo.c
@@ -0,0 +1,27 @@
+#include "ff.h"
+
+#include <math.h>
+#include <unistd.h>
+
+#define W 800
+#define H 600
+
+int main()
+{
+	pix_t pix[W * H] = {};
+	img_t img = { .w = W, .h = H, .pix = pix };
+
+	for (unsigned y = 0; y < H; ++y) {
+		for (unsigned x = 0; x < W; ++x) {
+			pix_t *out = pix + (W * y + x);
+			out->r = 0xffff * x / W;
+			out->g = 0;
+			out->b = 0xffff * y / H;
+			out->a = 0xffff;
+		}
+	}
+
+	ff_write(STDOUT_FILENO, img);
+
+	return 0;
+}