[PBR-Sky] The rest part of sky rendering

[roeas]

Atmospheric scattering is complete in #36 and i gathered informations from #2 and #39 to render the rest part of sky.

[roeas]

Volume Shadow algorithm

A volume shadow algorithm is needed to get the ray length in the shadow to get the ground truth light shaft effect.

[roeas]

Cloud

GPU Pro 7 has a awesome chapter about cloud rendering implementation. Real-Time Volumetric Cloudscapes - Andrew Schneider

THE REAL-TIME VOLUMETRIC CLOUDSCAPES OF HORIZON ZERO DAWN https://www.guerrilla-games.com/read/the-real-time-volumetric-cloudscapes-of-horizon-zero-dawn

Edited by @T-rvw :

• Topics
  • UV Animation
  • Cloud Modeling
  • Low/Medium/High layers in meters
  • Fractal Brownian Motion
  • Noise : Perlin(Gradient), Worley(Voronioi/Celluar)
  • Density-Height Functions
  • Weather Texture
  • Cloud Lighting
  • Attenuation : Beer's Law
  • Probability of light scattering : Henyey-Greenstein Phase Function
  • Cloud with Rains : darker(absorb more lights)
  • Types
  • VFX Cloud
  • VDB Cloud
  • Billboard Cloud
  • Raymarching Cloud

References:

• Sky Clounds in Frostbite
• Real-time rendering of volumetric clouds
• CSS3DClouds

[roeas]

God Rays / Light Shafts

This effect can also be achieved by some simple trick:

• https://www.shadertoy.com/view/4dyXWy
• https://developer.nvidia.com/gpugems/gpugems3/part-ii-light-and-shadows/chapter-13-volumetric-light-scattering-post-process

[roeas]

Challenge of Precomputed Atmospheric Scattering

• Precomputation Cost

  • Multi Scattering iterations are very expensive.
  • Hard to generate LUT on low-end devices.

• Authoring and Dynamic Adjustment of Environments

  • Artist can't change scattering coefficients on the fly.
  • Hard to render effects like weather from sunny to rain fog, space travel among planets.

• Resolvent

  • A Scalable and Production Ready Sky and Atmosphere Rendering Technique