Add front/back face detection

demo.c

@@ -4,6 +4,7 @@
 #include "ray.h"
 #include "vec3.h"
 
+#include <float.h>
 #include <limits.h>
 #include <math.h>
 #include <stdio.h>
@@ -34,7 +35,7 @@ static vec3_t raycol(ray_t ray)
 {
 	hit_t hit;
 	for (unsigned i = 0; i < NELEMS(scene); ++i) {
-		if (scene[i].intersect(scene[i].params, ray, &hit))
+		if (scene[i].intersect(scene[i].params, ray, &hit, 0.0, DBL_MAX))
 			return vec3_scale(vec3_add(hit.normal, white), 0.5);
 	}