Update volumetrics

client/shaders/clouds_merge/opengl_vertex.glsl

@@ -1,7 +1,48 @@
+uniform mat4 mCameraProjInv;
+uniform mat4 mCameraView;
+uniform vec3 v_LightDirection;
+uniform float f_timeofday;
+
+varying vec3 relativePosition;
+varying vec3 viewDirection;
 varying vec2 screenspaceCoordinate;
+varying vec3 sunTint;
+varying float auroraFactor;
+
+vec3 getDirectLightScatteringAtGround(vec3 v_LightDirection)
+{
+	// Based on talk at 2002 Game Developers Conference by Naty Hoffman and Arcot J. Preetham
+	const float beta_r0 = 1e-5; // Rayleigh scattering beta
+
+	// These factors are calculated based on expected value of scattering factor of 1e-5
+	// for Nitrogen at 532nm (green), 2e25 molecules/m3 in atmosphere
+	const vec3 beta_r0_l = vec3(3.3362176e-01, 8.75378289198826e-01, 1.95342379700656) * beta_r0; // wavelength-dependent scattering
+
+	const float atmosphere_height = 15000.; // height of the atmosphere in meters
+	// sun/moon light at the ground level, after going through the atmosphere
+	return exp(-beta_r0_l * atmosphere_height / (1e-5 - dot(v_LightDirection, vec3(0., 1., 0.))));
+}
+
+// custom smoothstep implementation because it's not defined in glsl1.2
+// https://docs.gl/sl4/smoothstep
+float mtsmoothstep(in float edge0, in float edge1, in float x)
+{
+	float t = clamp((x - edge0) / (edge1 - edge0), 0.0, 1.0);
+	return t * t * (3.0 - 2.0 * t);
+}
 
 void main(void)
 {
+	vec4 p = mCameraProjInv * inVertexPosition;
+	viewDirection = p.xyz / p.w;
+	relativePosition = (p.xyz / p.w) * mat3(mCameraView);
 	screenspaceCoordinate = inVertexPosition.xy;
+
+	auroraFactor = 1. - mtsmoothstep(0.13, 0.15, f_timeofday) * mtsmoothstep(0.87, 0.85, f_timeofday);
+
+	float tintFactor = mtsmoothstep(0.21, 0.24, f_timeofday) * mtsmoothstep(0.793, 0.753, f_timeofday);
+
+	sunTint = mix(vec3(1.0), getDirectLightScatteringAtGround(v_LightDirection), tintFactor);
+
 	gl_Position = inVertexPosition;
 }