static float ComputeOpticalLengthToTopAtmosphereBoundary(
AtmosphereConfig atmosphere, float r, float mu, float scale_height)
{
// Number of intervals for the numerical integration.
const int SAMPLE_COUNT = 500;
// The integration step, i.e. the length of each integration interval.
float dx =
DistanceToTopAtmosphereBoundary(atmosphere, r, mu) / (float)SAMPLE_COUNT;
// Integration loop.
float result = 0.0f;
for (int i = 0; i <= SAMPLE_COUNT; ++i)
{
float d_i = (float)i * dx;
// Distance between the current sample point and the planet center.
float r_i = Mathf.Sqrt(d_i * d_i + 2.0f * r * mu * d_i + r * r);
// Number density at the current sample point (divided by the number density
// at the bottom of the atmosphere, yielding a dimensionless number).
float y_i = GetScaleHeight(r_i - atmosphere.atmosphere_bot_radius, scale_height);
// Sample weight (from the trapezoidal rule).
float weight_i = i == 0 || i == SAMPLE_COUNT ? 0.5f : 1.0f;
result += y_i * weight_i * dx;
}
return(result);
}
public ProgressiveLutUpdater(AtmosphereConfig atmConfig, AtmLutGenerateConfig lutConfig, ITimeLogger logger = null)
{
this.atmConfigToUse = atmConfig;
this.lutConfig = lutConfig;
this.logger = logger;
working = false;
atmConfigUsedToUpdate = ScriptableObject.CreateInstance <AtmosphereConfig>();
}
static float DistanceToTopAtmosphereBoundary(AtmosphereConfig atmosphere,
float r, float mu)
{
float discriminant = r * r * (mu * mu - 1.0f) +
atmosphere.atmosphere_top_radius * atmosphere.atmosphere_top_radius;
return(ClampDistance(-r * mu + SafeSqrt(discriminant)));
}
public void CopyDataFrom(AtmosphereConfig config)
{
this.AtmosphereDensity = config.AtmosphereDensity;
this.LightingScale = config.LightingScale;
this.SunRadianceOnAtmosphere = config.SunRadianceOnAtmosphere;
this.atmosphere_top_radius = config.atmosphere_top_radius;
this.atmosphere_bot_radius = config.atmosphere_bot_radius;
this.atmosphere_sun_angular_radius = config.atmosphere_sun_angular_radius;
this.rayleigh_scattering = config.rayleigh_scattering;
this.rayleigh_scale_height = config.rayleigh_scale_height;
this.mie_scattering = config.mie_scattering;
this.mie_scale_height = config.mie_scale_height;
this.mie_phase_function_g = config.mie_phase_function_g;
this.ozone_extinction = config.ozone_extinction;
this.ozone_scale_height = config.ozone_scale_height;
}
public static Vector3 GetTransmittanceToSun(
AtmosphereConfig atmosphere,
float r, float mu_s)
{
float sin_theta_h = atmosphere.atmosphere_bot_radius / r;
float cos_theta_h = -Mathf.Sqrt(Mathf.Max(1.0f - sin_theta_h * sin_theta_h, 0.0f));
var transmittanceToCenter = ComputeTransmittanceToTopAtmosphereBoundary(
atmosphere, r, mu_s);
var lower_bound = -sin_theta_h * atmosphere.atmosphere_sun_angular_radius;
var upper_bound = sin_theta_h * atmosphere.atmosphere_sun_angular_radius;
var fraction = (mu_s - cos_theta_h - lower_bound) / (upper_bound - lower_bound);
fraction = Mathf.Clamp01(fraction);
return(transmittanceToCenter * fraction);
}
public static Vector3 ComputeTransmittanceToTopAtmosphereBoundary(
AtmosphereConfig atmosphere, float r, float mu)
{
Vector3 rayleigh = atmosphere.rayleigh_scattering_spectrum *
ComputeOpticalLengthToTopAtmosphereBoundary(
atmosphere, r, mu, atmosphere.rayleigh_scale_height);
Vector3 mie = Vector3.one * atmosphere.mie_extinction_spectrum *
ComputeOpticalLengthToTopAtmosphereBoundary(
atmosphere, r, mu, atmosphere.mie_scale_height);
Vector3 ozone = atmosphere.ozone_extinction_spectrum *
ComputeOpticalLengthToTopAtmosphereBoundary(
atmosphere, r, mu, atmosphere.ozone_scale_height);
var sum = rayleigh + mie + ozone;
return(new Vector3(
Mathf.Exp(-sum.x),
Mathf.Exp(-sum.y),
Mathf.Exp(-sum.z)
));
}
public static void ApplyComputeShaderParams(AtmLutGenerateConfig lutConfig, AtmosphereConfig atmConfig)
{
lutConfig.Apply(computeShader);
atmConfig.Apply(computeShader);
}
static float ClampRadius(AtmosphereConfig atmosphere, float r)
{
return(Mathf.Clamp(r, atmosphere.atmosphere_bot_radius, atmosphere.atmosphere_top_radius));
}
