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POC / Radiance Cascades

Trying to build up my intuition around Suslik's Radiance Cascades GI approach.

2D

Things are simpler in 2D so we'll start there.

Radiance Intervals (2D)

In 2D these are bands/shells/annuluses/crusts(🍕) of radiance values where relative to the previous level, each cascade level:

  • doubles the inner radius of the band
  • doubles the width of the band
  • doubles the number of rays per probe
  • halves the total number of rays
  • offsets the rays to avoid overlaps (e.g., angle = TAU * (rayIndex + 0.5) / rayCount)
level 0 ray count:
branching factor(Nlevel):

source: flatland-2d/radiance-intervals-2d.js

Ray Distributions (2D)

Note: this demo is limited to spatial doubling for cascade levels irregardless of the branching factor, which is the common case for flatland.

max level
2r raycount (level 0):
probe diameter (level 0):
interval radius (level 0):
branching factor(Nlevel):
color lower levels:
show cascade ray counts:

source: flatland-2d/probe-ray-distributions-2d.js

Probe Ray Interpolation (2D)

min level:
max level:
level 0 ray count:
branching factor(Nlevel):

source: flatland-2d/probe-interpolation-2d.js

Flatland (2D)

Debug/Development

run continuously and collect frame timings
timings 

      

    

    

    render world mip level
    
    

    

      render probe directions 
    

    

      disable brush preview 
    

    

      raymarch mipmap N on cascade level N 
    

    

      raymarch with dda
    

    

      raymarch fixed size step multiplier: 
      
    

    

      accumulate non-linearly
    

    

      accumulation decay: 
      
    

    

    
Radiance Cascade Parameters

    

      

        2i spacing (level 0): 
        
      

      

        2r raycount (level 0): 
        
      

      

        branching factor: 
        
      

      

        interval radius (level 0): 
        
      

      

        levels: 
        
      

    

    
Brush Parameters

    

      

        
      

      

        erase 
      

      

        brush opacity: 
        
      

      

        brush radiance: 
        
      

      

        brush radius: 
        
      

      

        brush color: 
      

    

  

  

    
    

      
      

        This demo requires WebGPU - in other words, you should open this page in Chrome or Edge.
      

    

  

  

    source: flatland-2d/flatland-2d.js
  

  



Screenspace probes with Worldspace Intervals (3D)



  

    Compute a storage cost table for screen-space probes with world space intervals
  



    
World Space

    

      

         probe directions
        
      

    

    
Screen Space

    

      

         probe spacing
        
      

    

    
General

    

      

         keep merged and unmerged cascades
        

          This keeps the data around that is used to compute reflections for surfaces defined by GGX or similar roughness models.
        

        
      

      

         place screenspace probes on min and max depth
        

          This helps with scenes that have high depth complexity with thin objects.
        

        
      

    

  

  

  

  

    source: ssprobes-wsintervals/ssprobes-wsintervals.js
  

  

World Space Probes (3D)



  

    Compute a storage cost table for world space probes, using a ping-pong buffer, at various
    spatial resolutions.
  

  
rayCount = 6
bytesPerRay = 16
diameter3 * rayCount * bytesPerRay * 2

  

    
      

        diameter
        megabytes
        MB per slice
      

    
    
    
  



Licensing


Text / Images


tmpvar's radiance cascades 2D playground is licensed under CC BY 4.0
 which includes the text and images on this page.

Linked Source Code


All of the linked source code is licensed MIT as specified in the header of each file.