From 9a9a88360a95f88700e66998ec5a89a54bb8ea22 Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Sat, 29 Mar 2025 00:45:45 +0300
Subject: [PATCH] Make Sun customizable!

---
 src/trace.wgsl | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/trace.wgsl b/src/trace.wgsl
index 79ba954..9a906cd 100644
--- a/src/trace.wgsl
+++ b/src/trace.wgsl
@@ -104,8 +104,22 @@ fn trace_fragment(in: Varying) -> vec3f {
 		if (sphere == -1) {
 			let theta = dot(ray, normalize(vec3(0., 0., 1.)));
 			var env: vec3f; // in kilonits
-			if (theta > 0.999988647254458) {
-				env = vec3(1.6e6, 1.5e6, 1.0e6);
+
+			const ILLUMINANCE_LUX = 1e5;
+			const ANGULAR_DIAMETER_DEG = 0.5; // Sun: 0.5°
+
+			const PI = 3.141592653589793;
+
+			const ANGULAR_DIAMETER_RAD = PI / 180.0 * ANGULAR_DIAMETER_DEG;
+			const THETA = 0.5 * ANGULAR_DIAMETER_RAD;
+			const COS_THETA = 1.0 - 0.5 * THETA * THETA; // approximately
+
+			const SOLID_ANGLE_SR = PI * THETA * THETA; // approximately
+			const LUMINANCE_NIT = ILLUMINANCE_LUX / SOLID_ANGLE_SR;
+			const LUMINANCE_KNIT = 1e-3 * LUMINANCE_NIT;
+
+			if (theta > COS_THETA) {
+				env = vec3(1.0, 0.9, 0.6) * LUMINANCE_KNIT;
 			} else {
 				env = mix(vec3(0.5, 1.0, 2.0), vec3(2.0, 3.0, 4.0), 0.5 * theta + 0.5);
 			}