HDR: Render the Moon, stars and planets

Moon textures have been adapted from the following webpage:

https://svs.gsfc.nasa.gov/4720
NASA's Scientific Visualization Studio

Effects/galaxy.eff

@@ -161,7 +161,4 @@
     
   </technique>
 
-  <technique n="109">
-    <scheme>hdr-geometry</scheme>
-  </technique>
 </PropertyList>

Effects/moon.eff

@@ -0,0 +1,122 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<PropertyList>
+  <name>Effects/moon</name>
+
+  <parameters>
+    <texture n="1">
+      <image>Textures/Sky/moon_color.png</image>
+      <type>2d</type>
+      <filter>linear-mipmap-linear</filter>
+      <mag-filter>linear-mipmap-linear</mag-filter>
+      <wrap-s>clamp-to-edge</wrap-s>
+      <wrap-t>clamp-to-edge</wrap-t>
+      <internal-format>normalized</internal-format>
+    </texture>
+    <texture n="2">
+      <image>Textures/Sky/moon_n.png</image>
+      <type>2d</type>
+      <filter>linear-mipmap-linear</filter>
+      <mag-filter>linear-mipmap-linear</mag-filter>
+      <wrap-s>clamp-to-edge</wrap-s>
+      <wrap-t>clamp-to-edge</wrap-t>
+      <internal-format>normalized</internal-format>
+    </texture>
+    <!-- exposure.glsl -->
+    <exposure-compensation>
+      <use>/sim/rendering/hdr/exposure-compensation</use>
+    </exposure-compensation>
+  </parameters>
+
+  <!-- Fixed-pipeline fallback -->
+  <technique n="11">
+    <pass>
+      <!--
+          An empty pass should be fine as we are filling the stateset manually
+          in simgear/scene/sky/moon.cxx
+      -->
+    </pass>
+  </technique>
+
+  <technique n="129">
+    <scheme>hdr-forward</scheme>
+    <pass>
+      <!-- Disable depth testing -->
+      <depth>
+        <enabled>false</enabled>
+      </depth>
+      <!-- Only render the moon on top of the skydome -->
+      <stencil>
+        <function>equal</function>
+        <value>0</value>
+      </stencil>
+      <!-- Make sure we render after the skydome -->
+      <render-bin>
+        <bin-number>-5</bin-number>
+        <bin-name>RenderBin</bin-name>
+      </render-bin>
+      <!-- Color map -->
+      <texture-unit>
+        <unit>1</unit>
+        <type><use>texture[1]/type</use></type>
+        <image><use>texture[1]/image</use></image>
+        <filter><use>texture[1]/filter</use></filter>
+        <mag-filter><use>texture[1]/mag-filter</use></mag-filter>
+        <wrap-s><use>texture[1]/wrap-s</use></wrap-s>
+        <wrap-t><use>texture[1]/wrap-t</use></wrap-t>
+      </texture-unit>
+      <!-- Normal map -->
+      <texture-unit>
+        <unit>2</unit>
+        <type><use>texture[2]/type</use></type>
+        <image><use>texture[2]/image</use></image>
+        <filter><use>texture[2]/filter</use></filter>
+        <mag-filter><use>texture[2]/mag-filter</use></mag-filter>
+        <wrap-s><use>texture[2]/wrap-s</use></wrap-s>
+        <wrap-t><use>texture[2]/wrap-t</use></wrap-t>
+      </texture-unit>
+      <cull-face>back</cull-face>
+      <!-- Additive blending to add the sky in-scattering from the skydome -->
+      <blend>
+        <active>true</active>
+        <source>one</source>
+        <destination>one</destination>
+      </blend>
+      <program>
+        <vertex-shader>Shaders/HDR/moon.vert</vertex-shader>
+        <fragment-shader>Shaders/HDR/moon.frag</fragment-shader>
+        <fragment-shader>Shaders/HDR/math.glsl</fragment-shader>
+        <fragment-shader>Shaders/HDR/color.glsl</fragment-shader>
+        <fragment-shader>Shaders/HDR/normalmap.glsl</fragment-shader>
+        <fragment-shader>Shaders/HDR/atmos_spectral.glsl</fragment-shader>
+        <fragment-shader>Shaders/HDR/exposure.glsl</fragment-shader>
+      </program>
+      <uniform>
+        <name>color_tex</name>
+        <type>sampler-2d</type>
+        <value type="int">1</value>
+      </uniform>
+      <uniform>
+        <name>normal_tex</name>
+        <type>sampler-2d</type>
+        <value type="int">2</value>
+      </uniform>
+      <uniform>
+        <name>transmittance_tex</name>
+        <type>sampler-2d</type>
+        <value type="int">12</value>
+      </uniform>
+      <!-- exposure.glsl -->
+      <uniform>
+        <name>lum_tex</name>
+        <type>sampler-2d</type>
+        <value type="int">14</value>
+      </uniform>
+      <uniform>
+        <name>exposure_compensation</name>
+        <type>float</type>
+        <value><use>exposure-compensation</use></value>
+      </uniform>
+    </pass>
+  </technique>
+</PropertyList>

Effects/stars.eff

@@ -3,6 +3,10 @@
 <PropertyList>
   <name>Effects/stars</name>
 
+  <parameters>
+    <max-radiance type="float">2.0</max-radiance>
+  </parameters>
+
   <!-- Fixed-pipeline fallback -->
   <technique n="11">
     <pass>
@@ -13,7 +17,32 @@
     </pass>
   </technique>
 
-  <technique n="109">
-    <scheme>hdr-geometry</scheme>
+  <technique n="129">
+    <scheme>hdr-forward</scheme>
+    <pass>
+      <depth>
+        <enabled>false</enabled>
+      </depth>
+      <!-- Only render the stars on top of the skydome -->
+      <stencil>
+        <function>equal</function>
+        <value>0</value>
+      </stencil>
+      <cull-face>off</cull-face>
+      <blend>
+        <active>true</active>
+        <source>src-alpha</source>
+        <destination>one-minus-src-alpha</destination>
+      </blend>
+      <program>
+        <vertex-shader>Shaders/HDR/stars.vert</vertex-shader>
+        <fragment-shader>Shaders/HDR/stars.frag</fragment-shader>
+      </program>
+      <uniform>
+        <name>max_radiance</name>
+        <type>float</type>
+        <value><use>max-radiance</use></value>
+      </uniform>
+    </pass>
   </technique>
 </PropertyList>

Shaders/HDR/bloom_downsample.frag

@@ -77,8 +77,6 @@ void main()
             kw4 * group4;
         downsample /= kw_sum;
     } else {
-        // Apply weighted distribution:
-        // 0.5 + 0.125 + 0.125 + 0.125 + 0.125 = 1
         downsample = e*0.125;
         downsample += (a+c+g+i)*0.03125;
         downsample += (b+d+f+h)*0.0625;

Shaders/HDR/moon.frag

@@ -0,0 +1,69 @@
+#version 330 core
+
+layout(location = 0) out vec4 fragColor;
+
+in VS_OUT {
+    vec2 texcoord;
+    vec3 vertex_normal;
+    vec3 view_vector;
+} fs_in;
+
+uniform sampler2D color_tex;
+uniform sampler2D transmittance_tex;
+
+uniform vec3 fg_SunDirection;
+uniform float fg_CameraDistanceToEarthCenter;
+uniform float fg_EarthRadius;
+uniform vec3 fg_CameraViewUp;
+
+const float ATMOSPHERE_RADIUS = 6471e3;
+
+// math.glsl
+float M_1_PI();
+// color.glsl
+vec3 eotf_inverse_sRGB(vec3 srgb);
+// normalmap.glsl
+vec3 perturb_normal(vec3 N, vec3 V, vec2 texcoord);
+// atmos_spectral.glsl
+vec4 get_sun_spectral_irradiance();
+vec3 linear_srgb_from_spectral_samples(vec4 L);
+// exposure.glsl
+vec3 apply_exposure(vec3 color);
+
+void main()
+{
+    vec3 albedo = eotf_inverse_sRGB(texture(color_tex, fs_in.texcoord).rgb);
+
+    vec3 N = normalize(fs_in.vertex_normal);
+    N = perturb_normal(N, fs_in.view_vector, fs_in.texcoord);
+
+    float NdotL = max(dot(N, fg_SunDirection), 0.0);
+
+    vec3 V = normalize(fs_in.view_vector);
+
+    // Simple Lambertian BRDF
+    vec3 color = albedo * M_1_PI() * NdotL
+        * linear_srgb_from_spectral_samples(get_sun_spectral_irradiance());
+
+    // Apply aerial perspective
+    float normalized_altitude =
+        (fg_CameraDistanceToEarthCenter - fg_EarthRadius)
+        / (ATMOSPHERE_RADIUS - fg_EarthRadius);
+    float cos_theta = dot(-V, fg_CameraViewUp);
+
+    vec2 uv = vec2(cos_theta * 0.5 + 0.5, clamp(normalized_altitude, 0.0, 1.0));
+    vec4 transmittance = texture(transmittance_tex, uv);
+
+    // The proper thing would be to have spectral albedo data for the moon,
+    // but that's too much work for little return. Just approximate the
+    // transmittance by taking the average of the four spectral samples.
+    color *= dot(transmittance, vec4(0.25));
+
+    // Pre-expose
+    color = apply_exposure(color);
+
+    // Final color = transmittance * moon color + sky inscattering
+    // In this frag shader we output the multiplication part, and the sky
+    // in-scattering is added by doing additive blending on top of the skydome.
+    fragColor = vec4(color, 1.0);
+}

Shaders/HDR/moon.vert

@@ -0,0 +1,24 @@
+#version 330 core
+
+layout(location = 0) in vec4 pos;
+layout(location = 1) in vec3 normal;
+layout(location = 2) in vec4 vertex_color;
+layout(location = 3) in vec4 multitexcoord0;
+
+out VS_OUT {
+    vec2 texcoord;
+    vec3 vertex_normal;
+    vec3 view_vector;
+} vs_out;
+
+uniform mat4 osg_ModelViewProjectionMatrix;
+uniform mat4 osg_ModelViewMatrix;
+uniform mat3 osg_NormalMatrix;
+
+void main()
+{
+    gl_Position = osg_ModelViewProjectionMatrix * pos;
+    vs_out.texcoord = multitexcoord0.st;
+    vs_out.vertex_normal = osg_NormalMatrix * normal;
+    vs_out.view_vector = (osg_ModelViewMatrix * pos).xyz;
+}

Shaders/HDR/shading_opaque.glsl

@@ -20,6 +20,7 @@ vec3 eval_ibl(vec3 base_color, float metallic, float roughness, vec3 f0,
               float occlusion, vec3 ws_N, vec3 ws_refl, float NdotV);
 // aerial_perspective.glsl
 vec3 add_aerial_perspective(vec3 color, vec2 coord, float depth);
+// sun.glsl
 vec3 get_sun_radiance(vec3 p);
 // clustered.glsl
 vec3 eval_scene_lights(vec3 base_color, float metallic, float roughness, vec3 f0,

Shaders/HDR/stars.frag

@@ -0,0 +1,14 @@
+#version 330 core
+
+layout(location = 0) out vec4 fragColor;
+
+in VS_OUT {
+    vec4 color;
+} fs_in;
+
+uniform float max_radiance;
+
+void main()
+{
+    fragColor = vec4(fs_in.color.rgb * max_radiance, fs_in.color.a);
+}

Shaders/HDR/stars.vert

@@ -0,0 +1,16 @@
+#version 330 core
+
+layout(location = 0) in vec4 pos;
+layout(location = 2) in vec4 vertex_color;
+
+out VS_OUT {
+    vec4 color;
+} vs_out;
+
+uniform mat4 osg_ModelViewProjectionMatrix;
+
+void main()
+{
+    gl_Position = osg_ModelViewProjectionMatrix * pos;
+    vs_out.color = vertex_color;
+}