From 1e31fae5d0ffc809ef4e36b02782368c45a99791 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Tue, 23 Sep 2025 15:36:08 +0100
Subject: [PATCH] Make samples per pixel a camera parameter

---
 demo.c           |  4 +++-
 include/camera.h |  3 ++-
 src/camera.c     | 15 +++++++--------
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/demo.c b/demo.c
index 23423d5..2d3e103 100644
--- a/demo.c
+++ b/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);
diff --git a/include/camera.h b/include/camera.h
index cf434f5..354f14c 100644
--- a/include/camera.h
+++ b/include/camera.h
@@ -11,11 +11,12 @@ typedef struct {
 	vec3_t pos;
 	vec3_t pix_origin, x_step, y_step;
 	uint32_t img_width, img_height;
+	unsigned samples_per_pixel;
 } camera_t;
 
 camera_t camera_init(
     vec3_t pos, double focal_len, double viewport_height, uint32_t img_width,
-    uint32_t img_height);
+    uint32_t img_height, unsigned samples_per_pixel);
 
 void camera_render(
     const camera_t *camera, const obj_t *scene, unsigned scene_count,
diff --git a/src/camera.c b/src/camera.c
index d923870..2a41393 100644
--- a/src/camera.c
+++ b/src/camera.c
@@ -11,14 +11,11 @@
 
 #define MAX_ITER 10
 #define MIN_T 1e-6
-
-#define NSAMPLES 100
-#define SAMPLE_WEIGHT (1.0 / (double)NSAMPLES)
 #define SAMPLE_STDDEV 0.333
 
 #define GAMMA 2.2
 
-#define NTHREADS 40
+#define NTHREADS 20
 
 typedef struct {
 	const camera_t *camera;
@@ -54,7 +51,7 @@ trace(ray_t ray, const obj_t *scene, unsigned scene_count, rng_t *rng)
 
 		vec3_t atten;
 		if (!material.scatter(material.params, hit, rng, &ray, &atten))
-			break;
+			return black;
 		colour = vec3_hadamard(colour, atten);
 	}
 
@@ -79,6 +76,7 @@ static int render_thread(void *arg)
 	work_slice_t *slice = (work_slice_t *)arg;
 	const camera_t *camera = slice->camera;
 	const uint32_t w = camera->img_width;
+	const double sample_weight = 1.0 / (double)camera->samples_per_pixel;
 
 	const unsigned stop_y = slice->start_y + slice->row_count;
 	for (unsigned y = slice->start_y; y < stop_y; ++y) {
@@ -88,7 +86,7 @@ static int render_thread(void *arg)
 			const vec3_t pix = vec3_add(row, vec3_scale(camera->x_step, x));
 
 			vec3_t colour = black;
-			for (unsigned i = 0; i < NSAMPLES; ++i) {
+			for (unsigned i = 0; i < camera->samples_per_pixel; ++i) {
 				const vec3_t jitter
 				    = rng_gaussian_xy(&slice->rng, SAMPLE_STDDEV);
 				const vec3_t offset = vec3_add(
@@ -102,7 +100,7 @@ static int render_thread(void *arg)
 				const vec3_t sample = trace(
 				    ray, slice->scene, slice->scene_count, &slice->rng);
 
-				colour = vec3_add(colour, vec3_scale(sample, SAMPLE_WEIGHT));
+				colour = vec3_add(colour, vec3_scale(sample, sample_weight));
 			}
 
 			setpix(colour, slice->pixels + (w * y + x));
@@ -116,7 +114,7 @@ static int render_thread(void *arg)
 
 camera_t camera_init(
     vec3_t pos, double focal_len, double viewport_height, uint32_t img_width,
-    uint32_t img_height)
+    uint32_t img_height, unsigned samples_per_pixel)
 {
 	const double aspect = (double)img_width / (double)img_height;
 	const double viewport_width = viewport_height * aspect;
@@ -138,6 +136,7 @@ camera_t camera_init(
 		.y_step = y_step,
 		.img_width = img_width,
 		.img_height = img_height,
+		.samples_per_pixel = samples_per_pixel,
 	};
 }