Implement Gaussian anti-aliasing

src/camera.c

@@ -4,12 +4,14 @@
 #include "rng.h"
 
 #include <float.h>
-#include <stdio.h>
 #include <threads.h>
 
 #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 NTHREADS 40
 
@@ -76,18 +78,23 @@ static int render_thread(void *arg)
 		    = vec3_add(camera->pix_origin, vec3_scale(camera->y_step, y));
 		for (unsigned x = 0; x < w; ++x) {
 			const vec3_t pix = vec3_add(row, vec3_scale(camera->x_step, x));
-			const ray_t ray = {
-				.orig = camera->pos,
-				.dir = vec3_unit(pix),
-			};
 
 			vec3_t colour = black;
 			for (unsigned i = 0; i < NSAMPLES; ++i) {
-				
-				const double weight = 1.0 / NSAMPLES;
+				const vec3_t jitter
+				    = rng_gaussian_xy(&slice->rng, SAMPLE_STDDEV);
+				const vec3_t offset = vec3_add(
+				    vec3_scale(camera->x_step, jitter.x),
+				    vec3_scale(camera->y_step, jitter.y));
+
+				const ray_t ray = {
+					.orig = camera->pos,
+					.dir = vec3_unit(vec3_add(pix, offset)),
+				};
 				const vec3_t sample = trace(
 				    ray, slice->scene, slice->scene_count, &slice->rng);
-				colour = vec3_add(colour, vec3_scale(sample, weight));
+
+				colour = vec3_add(colour, vec3_scale(sample, SAMPLE_WEIGHT));
 			}
 
 			setpix(colour, slice->pixels + (w * y + x));