From 1a92f70f699389219dbda42d175e7898cdbe7783 Mon Sep 17 00:00:00 2001
From: ladevieq <ladevie.quentin@gmail.com>
Date: Fri, 23 Jan 2026 17:46:37 +0100
Subject: Working transmittance shader

---
 shaders/transmittance_lut.comp | 61 +++++++++++++++++++++++-------------------
 1 file changed, 34 insertions(+), 27 deletions(-)

(limited to 'shaders')

diff --git a/shaders/transmittance_lut.comp b/shaders/transmittance_lut.comp
index 34adbae..bb7e621 100644
--- a/shaders/transmittance_lut.comp
+++ b/shaders/transmittance_lut.comp
@@ -13,14 +13,13 @@ layout(push_constant) uniform buffers {
     uint padding;
 } params;
 
-vec2 sphere_intersection ( in vec3 pos, in vec3 dir, float radius )
-{
-    float b = dot(pos, vec3(radius));
-    float c = dot(pos, pos) - radius * radius;
+vec2 sphere_intersection ( in vec3 orig, in vec3 dir, float radius ) {
+    float b = dot(orig, dir);
+    float c = dot(orig, orig) - radius * radius;
     float h = b * b - c;
     if (h < 0.f) return vec2(-1.f); // no intersection
-    h = sqrt( h );
-    return vec2( -b - h, -b + h );
+    h = sqrt(h);
+    return vec2(-b - h, -b + h);
 }
 
 vec3 rayleigh_scattering = vec3(5.802f, 13.558f, 33.1f);
@@ -31,14 +30,6 @@ vec3 mie_absorption = vec3(4.40f);
 
 void main() {
     ivec2 coords = ivec2(gl_GlobalInvocationID.xy);
-    vec3 out_color = vec3(0);
-    if (coords.x % 2 == 0 ) {
-        out_color = vec3(1);
-    }
-    if (coords.y % 2 == 1 ) {
-        out_color = vec3(1);
-    }
-    imageStore(images[nonuniformEXT(params.output_image_index)], coords, vec4(out_color, 1.0));
 
     const uint raymarching_steps = 10U;
 
@@ -46,41 +37,57 @@ void main() {
     const float top_radius = 6420.f;
     const float atmosphere_radius = top_radius - ground_radius;
 
-    vec2 uvs = coords / params.tex_size;
+    vec2 uvs = vec2(coords) / params.tex_size;
 
-    float mu = uvs.y * 2.f - 1.f;
-    float theta = acos(mu);
+    float cos_mu = uvs.y * 2.f - 1.f;
+    float mu = acos(cos_mu);
     float height = atmosphere_radius *  uvs.x;
 
     vec2 pos = vec2(0.f, ground_radius + height);
-    vec2 dir = vec2(mu, sin(theta));
-    vec3 transmittance = vec3(0.f);
+    vec2 dir = normalize(vec2(cos_mu, sin(mu)));
 
     // find ground hit
     float t = 0.f;
     vec2 ground_intersection = sphere_intersection(vec3(pos, 0.f), vec3(dir, 0.f), ground_radius);
+    t = max(max(ground_intersection.x, 0.f), ground_intersection.y);
     t = ground_intersection.x;
+    // vec4 val = vec4(vec3(0.f), 1.f);
+
+    vec2 top_intersection = sphere_intersection(vec3(pos, 0.f), vec3(dir, 0.f), top_radius);
+    // t = max(max(top_intersection.x, 0.f), top_intersection.y);
 
     // find atmosphere hit
     if (ground_intersection.y < 0.f) {
         vec2 top_intersection = sphere_intersection(vec3(pos, 0.f), vec3(dir, 0.f), top_radius);
+
         t = top_intersection.y;
+        // val.z = 1.f;
+    } else {
+        // val.y = 1.f;
     }
 
-    vec2 hit = pos + dir * t;
-    vec3 extinction = rayleigh_scattering + rayleigh_absorption + mie_scattering + mie_absorption;
-    vec3 total_extinction = vec3(0.f);
+    // val.x = t;
+    // imageStore(images[nonuniformEXT(params.output_image_index)], coords, val);
+    // return;
+    imageStore(images[nonuniformEXT(params.output_image_index)], coords, vec4(t, 0.f, 0.f, 1.f));
+    return;
+
+    vec3 transmittance = vec3(0.f);
 
     // raymarching
     float step = t / raymarching_steps;
-    for (float dist = 0.f; dist < t; dist += step) {
-        vec2 cur = pos + dir * dist;
-        dist += step;
+    for (uint step_index = 0U; step_index < raymarching_steps; step_index++) {
+        float r_d = exp(-height / 8.f);
+        vec3 r_e = rayleigh_scattering * r_d;
+        float m_d = exp(-height / 1.2f);
+        vec3 m_e = mie_scattering * m_d + mie_absorption;
 
-        total_extinction += extinction * step;
+        transmittance += (r_e + m_e) * step;
     }
 
-    vec4 color = vec4(exp(-total_extinction), 1.f);
+    vec4 color = vec4(exp(-transmittance), 1.f);
+    color.xyz = vec3(0.f);
+    color.x = t;
 
     imageStore(images[nonuniformEXT(params.output_image_index)], coords, color);
 }
-- 
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