POC / Radiance Cascades

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

paper
demo
Exilecon talk
implementations:
- shadertoy: Radiance Cascades implementation by fad - includes some temporal latency due to shadertoy limitations.
- shadertoy: Radiance Cascades 2d Smooth WIP - Suslik's fork of fad's work
blog posts / videos:
- Yaazarai wrote about Radiance Cascades on GM Shader Tuts
- SimonDev made a nice introductory video: Exploring a New Approach to Realistic Lighting: Radiance Cascades
calulators and other utilities
kornel made a calcualator to compute the optimal cascade interval lengths based on the penumbra angle, minimum light size and probe spacing.

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(N^level):

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

2^r raycount (level 0):

probe diameter (level 0):

interval radius (level 0):

branching factor(N^level):

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(N^level):

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):

2^r 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.