From f89a779b8fa822607feada2418d903e72db43a3c 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] Add camera aperture / depth-of-field

---
 demo.c           |  5 ++++-
 include/camera.h |  4 +++-
 src/camera.c     | 12 +++++++-----
 src/render.c     | 14 ++++++++++++--
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/demo.c b/demo.c
index 922b36a..ca5a918 100644
--- a/demo.c
+++ b/demo.c
@@ -13,6 +13,8 @@
 #define MIN_RAD 1.0
 
 #define FOV 90
+#define APERTURE 0.5
+#define FOCAL_LEN 100.0
 #define SAMPLES_PER_PIXEL 100
 
 static const vec3_t camera_pos = { -100.0, 25.0, -100.0 };
@@ -62,7 +64,8 @@ int main()
 		rand_obj(objs + i, &rng);
 
 	img_t img = { .pix = pixbuf };
-	camera_t camera = camera_init(camera_pos, target, FOV, W, H, APERTURE);
+	camera_t camera
+	    = camera_init(camera_pos, target, FOV, W, H, APERTURE, FOCAL_LEN);
 
 	const scene_t scene = {
 		.sky_colour = sky,
diff --git a/include/camera.h b/include/camera.h
index 6c282b7..53863a8 100644
--- a/include/camera.h
+++ b/include/camera.h
@@ -8,11 +8,13 @@
 typedef struct {
 	vec3_t pos;
 	vec3_t pix_origin, x_step, y_step;
+	vec3_t u_hat, v_hat;
 	uint32_t img_width, img_height;
+	double aperture;
 } camera_t;
 
 camera_t camera_init(
     vec3_t pos, vec3_t target, double fov, uint32_t img_width,
-    uint32_t img_height);
+    uint32_t img_height, double aperture, double focal_len);
 
 #endif
diff --git a/src/camera.c b/src/camera.c
index 3d618dd..a09e199 100644
--- a/src/camera.c
+++ b/src/camera.c
@@ -10,11 +10,8 @@ static const vec3_t up = { 0.0, 1.0, 0.0 };
 
 camera_t camera_init(
     vec3_t pos, vec3_t target, double fov, uint32_t img_width,
-    uint32_t img_height)
+    uint32_t img_height, double aperture, double focal_len)
 {
-	const vec3_t target_disp = vec3_sub(target, pos);
-	const double focal_len = vec3_len(target_disp);
-
 	const double fov_rad = M_PI * fov / 180.0;
 	const double aspect = (double)img_width / (double)img_height;
 	const double viewport_height = focal_len * tan(fov_rad / 2);
@@ -27,7 +24,9 @@ camera_t camera_init(
 	const vec3_t u = vec3_scale(u_hat, viewport_width);
 	const vec3_t v = vec3_scale(v_hat, -viewport_height);
 
-	const vec3_t topleft = vec3_sub(target, vec3_scale(vec3_add(u, v), 0.5));
+	const vec3_t topleft = vec3_sub(
+	    vec3_add(pos, vec3_scale(w_hat, focal_len)),
+	    vec3_scale(vec3_add(u, v), 0.5));
 
 	const vec3_t x_step = vec3_scale(u, 1.0 / (double)img_width);
 	const vec3_t y_step = vec3_scale(v, 1.0 / (double)img_height);
@@ -39,7 +38,10 @@ camera_t camera_init(
 		.pix_origin = pix_origin,
 		.x_step = x_step,
 		.y_step = y_step,
+		.u_hat = u_hat,
+		.v_hat = v_hat,
 		.img_width = img_width,
 		.img_height = img_height,
+		.aperture = aperture,
 	};
 }
diff --git a/src/render.c b/src/render.c
index c48db95..3e104d2 100644
--- a/src/render.c
+++ b/src/render.c
@@ -94,9 +94,19 @@ static int render_thread(void *arg)
 				    vec3_scale(camera->y_step, jitter.y));
 				const vec3_t jittered_pix = vec3_add(pix, offset);
 
+				vec3_t source = camera->pos;
+				if (camera->aperture != 0.0) {
+					const vec3_t pos
+					    = vec3_scale(rng_xy(&slice->rng), camera->aperture);
+					const vec3_t offset = vec3_add(
+					    vec3_scale(camera->u_hat, pos.x),
+					    vec3_scale(camera->v_hat, pos.y));
+					source = vec3_add(source, offset);
+				}
+
 				const ray_t ray = {
-					.orig = camera->pos,
-					.dir = vec3_unit(vec3_sub(jittered_pix, camera->pos)),
+					.orig = source,
+					.dir = vec3_unit(vec3_sub(jittered_pix, source)),
 				};
 				const vec3_t sample = trace(ray, slice->scene, &slice->rng);