Screen-Space Global Illumination

Gather colored diffuse light bouncing between surfaces that are visible in the current frame. createSSGICompositeShaderPass traces a screen-space hemisphere, reprojects indirect-light history, denoises across compatible surfaces, and adds the stabilized radiance to scene color.

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At a Glance

Property	Value
Export	createSSGICompositeShaderPass
Backend	WebGPU
Render passes	Six: hemisphere trace, temporal resolve, depth history, two spatial filters, and composite
Required bindings	depthTexture, normalTexture, and velocityTexture
Persistent state	rgba16float indirect-light and depth history
Lighting model	Visible-screen diffuse bounce; no offscreen geometry

Usage

import {ShaderPassRenderer} from '@luma.gl/engine';
import {createGTAOCompositeShaderPass, createSSGICompositeShaderPass} from '@luma.gl/engine/effects';

const renderer = new ShaderPassRenderer(device, {
  colorFormat: 'rgba16float',
  shaderPasses: [
    createGTAOCompositeShaderPass(),
    createSSGICompositeShaderPass({resolutionScale: 0.5})
  ]
});

renderer.renderToScreen({
  sourceTexture: litSceneTexture,
  bindings: gBuffer.getShaderPassBindings(),
  uniforms: {
    ssgiTrace: {
      projectionMatrix,
      inverseProjectionMatrix,
      radius: 4.5,
      thickness: 0.32,
      intensity: 2.2,
      rayCount: 7,
      stepCount: 8,
      frameIndex
    },
    ssgiTemporal: {inverseProjectionMatrix, historyWeight: 0.89, depthThreshold: 0.022}
  }
});

Parameters

Parameter	Default	Range or purpose
resolutionScale	1	Relative resolution of tracing, history, denoising, and indirect-radiance textures.
radius	4.5	View-space hemisphere tracing distance.
thickness	0.32	Depth thickness accepted when a ray intersects visible scene geometry.
intensity	2.2	Multiplier applied to gathered diffuse bounced radiance.
rayCount	7	Hemisphere directions per pixel; supported range is 1 to 12.
stepCount	8	Samples per ray; supported range is 2 to 12.
historyWeight	0.89	Contribution from depth-validated indirect-light history.
depthThreshold	0.022	Temporal depth rejection threshold.
strength	1	Final ssgiComposite contribution added to scene color.

Quality and Limitations

The trace cost grows with both rayCount and stepCount, while resolution affects every intermediate and history texture. Only geometry and radiance visible in the current screen can contribute; offscreen emitters and surfaces hidden behind the first depth layer are unavailable. Velocity reprojection and depth/normal-aware denoising reduce frame-to-frame noise but do not recover missing scene information.

Place SSGI after direct lighting and ambient occlusion. Place it before Screen-Space Reflections when reflective surfaces should include the newly added diffuse bounce.

Related Effects

• GTAO removes unavailable ambient lighting instead of adding bounced radiance.
• Screen-Space Reflections gathers directional specular reflection.
• Depth-Aware Blur explains edge-preserving screen-space denoising.