X-Git-Url: http://git.tdb.fi/?a=blobdiff_plain;f=builtin_data%2F_sky.glsl;fp=builtin_data%2F_sky.glsl;h=45ca330dd80afd89f7845f07d353fc8f5fe2d4e5;hb=06d83c11e10208478487dea864ddd7822630c391;hp=0000000000000000000000000000000000000000;hpb=e98956208676c77e74462f17932ac530077a0540;p=libs%2Fgl.git

diff --git a/builtin_data/_sky.glsl b/builtin_data/_sky.glsl
new file mode 100644
index 00000000..45ca330d
--- /dev/null
+++ b/builtin_data/_sky.glsl
@@ -0,0 +1,138 @@
+struct AtmosphericEvents
+{
+	vec3 rayleigh_scatter;
+	vec3 mie_scatter;
+	vec3 mie_absorb;
+	vec3 ozone_absorb;
+};
+
+uniform Atmosphere
+{
+	AtmosphericEvents events;
+	float rayleigh_density_decay;
+	float mie_density_decay;
+	float ozone_band_center;
+	float ozone_band_extent;
+	float planet_radius;
+	float atmosphere_thickness;
+	vec3 ground_albedo;
+	int n_steps;
+};
+
+uniform View
+{
+	float view_height;
+	vec4 light_color;
+	vec3 light_dir;
+};
+
+struct OpticalPathInfo
+{
+	vec3 optical_depth;
+	vec3 luminance;
+};
+
+const float pi = 3.1415926535;
+const float mie_asymmetry = 0.8;
+
+uniform sampler2D transmittance_lookup;
+
+vec3 rayleigh_density(vec3 base, float height)
+{
+	return base*exp(height/rayleigh_density_decay);
+}
+
+float rayleigh_phase(float cos_theta)
+{
+	return 3.0*(1.0+cos_theta*cos_theta)/(16.0*pi);
+}
+
+vec3 mie_density(vec3 base, float height)
+{
+	return base*exp(height/mie_density_decay);
+}
+
+float mie_phase(float cos_theta)
+{
+	float g = mie_asymmetry;
+	float num = (1.0-g*g)*(1.0+cos_theta*cos_theta);
+	float denom = (2.0+g*g)*pow(1.0+g*g-2.0*g*cos_theta, 1.5);
+	return 3.0/(8.0*pi)*num/denom;
+}
+
+vec3 ozone_density(vec3 base, float height)
+{
+	return base*max(1.0-abs(height-ozone_band_center)/ozone_band_extent, 0.0);
+}
+
+AtmosphericEvents calculate_events(float height)
+{
+	AtmosphericEvents ev;
+	ev.rayleigh_scatter = rayleigh_density(events.rayleigh_scatter, height);
+	ev.mie_scatter = mie_density(events.mie_scatter, height);
+	ev.mie_absorb = mie_density(events.mie_absorb, height);
+	ev.ozone_absorb = ozone_density(events.ozone_absorb, height);
+	return ev;
+}
+
+vec3 total_extinction(AtmosphericEvents ev)
+{
+	return ev.rayleigh_scatter+ev.mie_scatter+ev.mie_absorb+ev.ozone_absorb;
+}
+
+float ray_sphere_intersect(vec3 ray_start, vec3 ray_dir, vec3 sphere_center, float sphere_radius)
+{
+	float t = dot(sphere_center-ray_start, ray_dir);
+	vec3 nearest = ray_start+t*ray_dir-sphere_center;
+	float d_sq = dot(nearest, nearest);
+	float r_sq = sphere_radius*sphere_radius;
+	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;
+}
+
+#pragma MSP stage(fragment)
+OpticalPathInfo raymarch_path(float start_height, vec3 look_dir)
+{
+	float cos_theta = dot(look_dir, light_dir);
+	float p_rayleigh = rayleigh_phase(cos_theta);
+	float p_mie = mie_phase(cos_theta);
+
+	vec3 planet_center = vec3(0.0, 0.0, -planet_radius);
+	vec3 pos = vec3(0.0, 0.0, start_height);
+	vec3 path_luminance = vec3(0.0);
+	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 ray_length = (ground_t>0.0 ? ground_t : space_t);
+	float step_size = ray_length/n_steps;
+
+	for(int i=0; i<=n_steps; ++i)
+	{
+		vec3 from_center = pos-planet_center;
+		float height = length(from_center);
+		float light_z = dot(from_center/height, light_dir);
+		height -= planet_radius;
+
+		AtmosphericEvents ev = calculate_events(height);
+		vec3 transmittance = exp(-path_extinction);
+		vec3 in_transmittance = texture(transmittance_lookup, vec2(sqrt(height/atmosphere_thickness), light_z)).rgb;
+		vec3 in_luminance = (ev.rayleigh_scatter*p_rayleigh+ev.mie_scatter*p_mie)*step_size;
+		if(i==n_steps && ground_t>0.0)
+			in_luminance += ground_albedo*light_z/pi;
+		path_luminance += transmittance*in_transmittance*in_luminance;
+
+		path_extinction += total_extinction(ev)*step_size;
+		pos += look_dir*step_size;
+	}
+
+	return OpticalPathInfo(path_extinction, path_luminance);
+}