From 43670cbfbab7bb128cf906ef924c473801a58482 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cobrien@witekio.com>
Date: Tue, 23 Sep 2025 15:35:26 +0100
Subject: [PATCH] Randomise scene

---
 demo.c        | 67 +++++++++++++++++++++++++++++++++++++--------------
 include/rng.h |  2 ++
 src/rng.c     | 30 +++++++++++------------
 3 files changed, 66 insertions(+), 33 deletions(-)

diff --git a/demo.c b/demo.c
index 07e6d64..e82da25 100644
--- a/demo.c
+++ b/demo.c
@@ -7,40 +7,71 @@
 
 #define W 800
 #define H 600
+
+#define OBJ_COUNT 32
+
+#define MAX_DIST 100.0
+#define MAX_RAD 10.0
+#define MIN_RAD 1.0
+
 #define FOV 90
 #define SAMPLES_PER_PIXEL 100
 
-#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
-
-static const vec3_t camera_pos = { 0.0, 1.5, -2.0 };
-static const vec3_t camera_target = { 0.0, 1.0, 1.0 };
+static const vec3_t camera_pos = { -100.0, 25.0, -100.0 };
+static const vec3_t target = { 0.0, 0.0, 0.0 };
 
 static const vec3_t sky = { 0.6, 0.7, 1.0 };
 
-static const obj_t objs[] = {
-	SPHERE(1.0, 1.0, 3.0, 1.0, LAMBERTIAN(0.6, 0.2, 0.8)),
-	SPHERE(-0.8, 1.0, 3.8, 1.0, LAMBERTIAN(1.0, 1.0, 1.0)),
-	SPHERE(-1.0, 0.2, 2.6, 0.2, LAMBERTIAN(0.2, 0.9, 0.3)),
-	SPHERE(0.3, 0.3, 1.8, 0.3, LAMBERTIAN(0.9, 0.6, 0.2)),
-	SPHERE(-1.6, 0.2, 2.0, 0.2, REFLECTIVE(1.0, 0.9, 0.4, 0.0)),
-	SPHERE(-6.0, 6.0, 5.0, 6.0, REFLECTIVE(0.9, 0.9, 0.9, 0.05)),
-	SPHERE(-0.7, 0.25, 1.5, 0.25, DIELECTRIC(1.5)),
-	SPHERE(0.0, -1000.0, 0.0, 1000.0, LAMBERTIAN(0.3, 0.3, 0.3)),
+static const material_t floor = LAMBERTIAN(1.0, 0.94, 0.80);
+static const material_t gold = REFLECTIVE(1.0, 0.9, 0.5, 0.0);
+static const material_t silver = REFLECTIVE(0.9, 0.9, 0.9, 0.0);
+static const material_t bronze = REFLECTIVE(0.9, 0.7, 0.5, 0.0);
+static const material_t glass = DIELECTRIC(1.5);
+
+static const material_t metals[] = { gold, silver, bronze };
+
+static obj_t objs[OBJ_COUNT] = {
+	[0] = SPHERE(0.0, -100000.0, 0.0, 100000.0, floor),
 };
 
 static pix_t pixbuf[W * H];
 
+static void rand_obj(obj_t *out, rng_t *rng)
+{
+	material_t material;
+	const uint32_t rand = rng_uint32(rng);
+	if (rand % 2 == 0) {
+		const double r = rng_canon(rng);
+		const double g = rng_canon(rng);
+		const double b = rng_canon(rng);
+		material = (material_t)LAMBERTIAN(r, g, b);
+	} else if (rand % 3 == 0) {
+		material = glass;
+	} else {
+		material = metals[rng_uint32(rng) % 3];
+	}
+
+	const double r = MIN_RAD + (MAX_RAD - MIN_RAD) * rng_canon(rng);
+	const double x = MAX_DIST * rng_disc(rng);
+	const double z = MAX_DIST * rng_disc(rng);
+	*out = (obj_t)SPHERE(x, r, z, r, material);
+}
+
 int main()
 {
+	rng_t rng = rng_init(0);
+	for (int i = 1; i < OBJ_COUNT; ++i)
+		rand_obj(objs + i, &rng);
+
+	img_t img = { .pix = pixbuf };
+	camera_t camera
+	    = camera_init(camera_pos, target, FOV, W, H, SAMPLES_PER_PIXEL);
+
 	const scene_t scene = {
 		.sky_colour = sky,
 		.objs = objs,
-		.obj_count = NELEMS(objs),
+		.obj_count = OBJ_COUNT,
 	};
-
-	img_t img = { .pix = pixbuf };
-	camera_t camera = camera_init(
-	    camera_pos, camera_target, FOV, W, H, SAMPLES_PER_PIXEL);
 	camera_render(&camera, &scene, &img);
 
 	ff_write(STDOUT_FILENO, img);
diff --git a/include/rng.h b/include/rng.h
index 0d422f4..2ff4800 100644
--- a/include/rng.h
+++ b/include/rng.h
@@ -10,7 +10,9 @@ typedef struct {
 } rng_t;
 
 rng_t rng_init(unsigned seed);
+uint32_t rng_uint32(rng_t *rng);
 double rng_canon(rng_t *rng);
+double rng_disc(rng_t *rng);
 vec3_t rng_vec3(rng_t *rng);
 vec3_t rng_gaussian_xy(rng_t *rng, double stddev);
 
diff --git a/src/rng.c b/src/rng.c
index 7cc508a..acc5e6a 100644
--- a/src/rng.c
+++ b/src/rng.c
@@ -9,7 +9,14 @@
 #define M_PI 3.14159265258979323846264
 #endif
 
-static uint32_t next(rng_t *rng)
+rng_t rng_init(unsigned seed)
+{
+	struct timeval tv;
+	gettimeofday(&tv, nullptr);
+	return (rng_t) { .state = tv.tv_usec + seed };
+}
+
+uint32_t rng_uint32(rng_t *rng)
 {
 	uint32_t x = rng->state;
 	x ^= x << 13;
@@ -18,26 +25,19 @@ static uint32_t next(rng_t *rng)
 	return rng->state = x;
 }
 
-static double disc(rng_t *rng)
+double rng_canon(rng_t *rng)
+{
+	return (double)rng_uint32(rng) / (double)UINT32_MAX;
+}
+
+double rng_disc(rng_t *rng)
 {
 	return 2.0 * rng_canon(rng) - 1.0;
 }
 
-rng_t rng_init(unsigned seed)
-{
-	struct timeval tv;
-	gettimeofday(&tv, nullptr);
-	return (rng_t) { .state = tv.tv_usec + seed };
-}
-
-double rng_canon(rng_t *rng)
-{
-	return (double)next(rng) / (double)UINT32_MAX;
-}
-
 vec3_t rng_vec3(rng_t *rng)
 {
-	const vec3_t v = { disc(rng), disc(rng), disc(rng) };
+	const vec3_t v = { rng_disc(rng), rng_disc(rng), rng_disc(rng) };
 	return vec3_unit(v);
 }