Parallelise rendering

src/rng.c

@@ -1,23 +1,31 @@
 #include "rng.h"
 
 #include <limits.h>
-#include <stdlib.h>
 #include <sys/time.h>
 
-void rng_init()
+static uint32_t next(rng_t *rng)
+{
+	uint32_t x = rng->state;
+	x ^= x << 13;
+	x ^= x >> 17;
+	x ^= x << 5;
+	return rng->state = x;
+}
+
+rng_t rng_init(unsigned seed)
 {
 	struct timeval tv;
-	gettimeofday(&tv, NULL);
-	srand(tv.tv_usec);
+	gettimeofday(&tv, nullptr);
+	return (rng_t) { .state = tv.tv_usec + seed };
 }
 
-double rng_double()
+double rng_double(rng_t *rng)
 {
-	return 2.0 * (double)rand() / (double)INT_MAX - 1.0;
+	return 2.0 * (double)next(rng) / (double)UINT32_MAX - 1.0;
 }
 
-vec3_t rng_vec3()
+vec3_t rng_vec3(rng_t *rng)
 {
-	const vec3_t v = { rng_double(), rng_double(), rng_double() };
+	const vec3_t v = { rng_double(rng), rng_double(rng), rng_double(rng) };
 	return vec3_unit(v);
 }