From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 5 May 2021 15:35:34 +0000 (+0300)
Subject: Modify sunlight color based on transmittance of the atmosphere
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=a266f0f915827b20591f6244ccc36129e844f408;p=libs%2Fgl.git

Modify sunlight color based on transmittance of the atmosphere
---

diff --git a/demos/desertpillars/source/desertpillars.cpp b/demos/desertpillars/source/desertpillars.cpp
index 5f3b29b1..bdbc069e 100644
--- a/demos/desertpillars/source/desertpillars.cpp
+++ b/demos/desertpillars/source/desertpillars.cpp
@@ -34,7 +34,7 @@ DesertPillars::DesertPillars(int, char **):
 	window.signal_close.connect(sigc::bind(sigc::mem_fun(this, &DesertPillars::exit), 0));
 	keyboard.signal_button_press.connect(sigc::bind_return(sigc::mem_fun(this, &DesertPillars::key_press), false));
 
-	const GL::Light &sun = resources.get<GL::Light>("Sun.light");
+	GL::Light &sun = resources.get<GL::Light>("Sun.light");
 	sky = make_unique<GL::Sky>(content, sun);
 
 	unsigned shadow_size = 8192;
diff --git a/source/effects/sky.cpp b/source/effects/sky.cpp
index baf4864a..9a5f73bc 100644
--- a/source/effects/sky.cpp
+++ b/source/effects/sky.cpp
@@ -1,3 +1,5 @@
+#include <msp/geometry/hypersphere.h>
+#include <msp/geometry/ray.h>
 #include "light.h"
 #include "mesh.h"
 #include "renderer.h"
@@ -9,7 +11,7 @@ using namespace std;
 namespace Msp {
 namespace GL {
 
-Sky::Sky(Renderable &r, const Light &s):
+Sky::Sky(Renderable &r, Light &s):
 	Effect(r),
 	sun(s),
 	transmittance_lookup(128, 64, (RENDER_COLOR, RGB16F)),
@@ -29,8 +31,9 @@ Sky::Sky(Renderable &r, const Light &s):
 	set_view_height(5.0f);
 }
 
-void Sky::set_planet(const Planet &planet)
+void Sky::set_planet(const Planet &p)
 {
+	planet = p;
 	shdata.uniform("events.rayleigh_scatter", planet.rayleigh_scatter.r, planet.rayleigh_scatter.g, planet.rayleigh_scatter.b);
 	shdata.uniform("events.mie_scatter", planet.mie_scatter.r, planet.mie_scatter.g, planet.mie_scatter.b);
 	shdata.uniform("events.mie_absorb", planet.mie_absorb.r, planet.mie_absorb.g, planet.mie_absorb.b);
@@ -46,9 +49,45 @@ void Sky::set_planet(const Planet &planet)
 
 void Sky::set_view_height(float h)
 {
+	view_height = h;
 	shdata.uniform("view_height", h);
 }
 
+Color Sky::get_transmittance(const Vector3 &look_dir)
+{
+	Vector3 pos(0.0f, 0.0f, view_height);
+	Vector3 planet_center(0.0f, 0.0f, -planet.planet_radius);
+
+	Geometry::Ray<float, 3> ray(pos-planet_center, look_dir);
+	Geometry::HyperSphere<float, 3> surface(planet.planet_radius);
+	Geometry::SurfacePoint<float, 3> intersection;
+	if(surface.get_intersections(ray, &intersection, 1))
+		return Color(0.0f);
+
+	Geometry::HyperSphere<float, 3> space(planet.planet_radius+planet.atmosphere_thickness);
+	if(!space.get_intersections(ray, &intersection, 1))
+		return Color(1.0f);
+
+	float step_size = intersection.distance/50;
+
+	Color path_extinction(0.0f);
+	for(unsigned i=0; i<50; ++i)
+	{
+		Vector3 from_center = pos-planet_center;
+		float height = from_center.norm()-planet.planet_radius;
+
+		Color rayleigh_scatter = planet.rayleigh_scatter*exp(height/planet.rayleigh_density_decay);
+		Color mie_scatter = planet.mie_scatter*exp(height/planet.mie_density_decay);
+		Color mie_absorb = planet.mie_absorb*exp(height/planet.mie_density_decay);
+		Color ozone_absorb = planet.ozone_absorb*max(1.0f-abs(height-planet.ozone_band_center)/planet.ozone_band_extent, 0.0f);
+
+		path_extinction = path_extinction+(rayleigh_scatter+mie_scatter+mie_absorb+ozone_absorb)*step_size;
+		pos += look_dir*step_size;
+	}
+
+	return Color(exp(-path_extinction.r), exp(-path_extinction.g), exp(-path_extinction.b));
+}
+
 void Sky::setup_frame(Renderer &renderer)
 {
 	if(rendered)
@@ -58,6 +97,7 @@ void Sky::setup_frame(Renderer &renderer)
 
 	shdata.uniform("light_color", sun.get_color());
 	shdata.uniform("light_dir", sun.get_position().slice<3>(0));
+	sun.set_transmittance(get_transmittance(normalize(sun.get_position().slice<3>(0))));
 
 	Renderer::Push push(renderer);
 
diff --git a/source/effects/sky.h b/source/effects/sky.h
index faa3eb03..5f84c861 100644
--- a/source/effects/sky.h
+++ b/source/effects/sky.h
@@ -41,7 +41,8 @@ public:
 	};
 
 private:
-	const Light &sun;
+	Planet planet;
+	Light &sun;
 	RenderTarget transmittance_lookup;
 	const Program &transmittance_shprog;
 	bool transmittance_lookup_dirty;
@@ -52,14 +53,17 @@ private:
 	const Sampler &sampler;
 	const Sampler &wrap_sampler;
 	mutable ProgramData shdata;
+	float view_height;
 	bool rendered;
 
 public:
-	Sky(Renderable &, const Light &);
+	Sky(Renderable &, Light &);
 
 	void set_planet(const Planet &);
 	void set_view_height(float);
 
+	Color get_transmittance(const Vector3 &);
+
 	virtual void setup_frame(Renderer &);
 	virtual void finish_frame();
 	virtual void render(Renderer &, Tag = Tag()) const;
diff --git a/source/materials/light.cpp b/source/materials/light.cpp
index d84be2ac..2825b81e 100644
--- a/source/materials/light.cpp
+++ b/source/materials/light.cpp
@@ -12,6 +12,7 @@ namespace GL {
 
 Light::Light():
 	color(1),
+	transmittance(1),
 	position(0, 0, 1, 0),
 	spot_dir(0, 0, -1),
 	spot_exp(0),
@@ -44,6 +45,11 @@ void Light::set_color(const Color &c)
 	color = c;
 }
 
+void Light::set_transmittance(const Color &t)
+{
+	transmittance = t;
+}
+
 void Light::set_matrix(const Matrix &m)
 {
 	Placeable::set_matrix(m);
@@ -101,7 +107,7 @@ void Light::update_shader_data(ProgramData &shdata, const Matrix &view_matrix, u
 {
 	string base = format("light_sources[%d]", i);
 	shdata.uniform(base+".position", view_matrix*position);
-	shdata.uniform(base+".color", color.r, color.g, color.b);
+	shdata.uniform(base+".color", color.r*transmittance.r, color.g*transmittance.g, color.b*transmittance.b);
 }
 
 
diff --git a/source/materials/light.h b/source/materials/light.h
index d097d04a..d4b66077 100644
--- a/source/materials/light.h
+++ b/source/materials/light.h
@@ -44,6 +44,7 @@ public:
 
 private:
 	Color color;
+	Color transmittance;
 	Vector4 position;
 	Vector3 spot_dir;
 	Vector3 direction;
@@ -62,7 +63,12 @@ public:
 	to shaders as light_sources[i].color. */
 	void set_color(const Color &);
 
+	/** Sets a multiplier on how much light actually reaches the target.  Used
+	when modeling an atmosphere. */
+	void set_transmittance(const Color &);
+
 	const Color &get_color() const { return color; }
+	const Color &get_transmittance() const { return transmittance; }
 
 	DEPRECATED void set_diffuse(const Color &c) { set_color(c); }
 	DEPRECATED void set_specular(const Color &) { }