From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 16 Oct 2021 15:34:15 +0000 (+0300)
Subject: Tweak the logic in sky raymarching to avoid false shadowing
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=0542080f04c13236dc04a4f19e8a30016ad86bfa;p=libs%2Fgl.git

Tweak the logic in sky raymarching to avoid false shadowing

Ray_sphere_intersection now always returns the ingoing hit if radius is
positive or outgoing hit if radius is negative.  This avoids a ray
starting at ground level towards the sky immediately hitting the ground.
---

diff --git a/builtin_data/_sky.glsl b/builtin_data/_sky.glsl
index 81f9d163..1dbda579 100644
--- a/builtin_data/_sky.glsl
+++ b/builtin_data/_sky.glsl
@@ -88,13 +88,8 @@ float ray_sphere_intersect(vec3 ray_start, vec3 ray_dir, vec3 sphere_center, flo
 	if(d_sq>r_sq)
 		return -1.0;
 
-	float offset = sqrt(r_sq-d_sq);
-	if(offset<t)
-		return t-offset;
-	else if(offset>-t)
-		return t+offset;
-	else
-		return -1.0;
+	float offset = sqrt(r_sq-d_sq)*sign(sphere_radius);
+	return t-offset;
 }
 
 #pragma MSP stage(fragment)
@@ -110,7 +105,7 @@ OpticalPathInfo raymarch_path(float start_height, vec3 look_dir)
 	vec3 path_extinction = vec3(0.0);
 
 	float ground_t = ray_sphere_intersect(pos, look_dir, planet_center, planet_radius);
-	float space_t = ray_sphere_intersect(pos, look_dir, planet_center, planet_radius+atmosphere_thickness);
+	float space_t = ray_sphere_intersect(pos, look_dir, planet_center, -(planet_radius+atmosphere_thickness));
 	float ray_length = (ground_t>0.0 ? ground_t : space_t);
 	float step_size = ray_length/n_steps;
 
@@ -123,7 +118,7 @@ OpticalPathInfo raymarch_path(float start_height, vec3 look_dir)
 
 		AtmosphericEvents ev = calculate_events(height);
 		vec3 transmittance = exp(-path_extinction);
-		float in_ground_t = ray_sphere_intersect(pos+light_dir, light_dir, planet_center, planet_radius);
+		float in_ground_t = ray_sphere_intersect(pos, light_dir, planet_center, planet_radius);
 		if(in_ground_t<0.0)
 		{
 			vec3 in_transmittance = texture(transmittance_lookup, vec2(sqrt(height/atmosphere_thickness), light_z)).rgb;