Make samples per pixel a camera parameter

demo.c

@@ -9,6 +9,7 @@
 #define H 600
 #define FOCAL_LEN 1.0
 #define VIEWPORT_H 2.0
+#define SAMPLES_PER_PIXEL 100
 
 #define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
 
@@ -30,7 +31,8 @@ static pix_t pixbuf[W * H];
 int main()
 {
 	img_t img = { .pix = pixbuf };
-	camera_t camera = camera_init(camera_pos, FOCAL_LEN, VIEWPORT_H, W, H);
+	camera_t camera = camera_init(
+	    camera_pos, FOCAL_LEN, VIEWPORT_H, W, H, SAMPLES_PER_PIXEL);
 	camera_render(&camera, scene, NELEMS(scene), &img);
 
 	ff_write(STDOUT_FILENO, img);