BT- Spectral Fog: Next Gen Volumetric Fog for URP

Temporally-stable volumetric fog for URP: quarter-res raymarch, TAA-style reprojection, local fog volumes, sun/point light scattering, APV support, and a one-click height auto-fit tool."

Technical Details

Render Pipeline & Version Requirements

• Universal Render Pipeline (URP) only — not compatible with Built-in Render Pipeline or HDRP
• Full Render Graph support on Unity 6.x
• Compatibility Mode fallback path included for URP versions predating Unity 6's Render Graph (same feature set, legacy ScriptableRenderPass.Execute path)
• Adaptive Probe Volume contribution requires Unity 2023.1 or newer — gracefully compiles out on older versions, all other features unaffected

Rendering Requirements

• Requires camera depth texture and motion vector texture (ScriptableRenderPassInput.Depth | Motion) — configured automatically by the renderer feature, no manual setup needed
• Compatible with both the Forward and Forward+ rendering paths
• Main light shadows (cascade and screen-space) and additional light shadows both supported
• Perspective and orthographic cameras both supported

Performance & Scaling

• Configurable raymarch resolution: Half or Quarter relative to camera resolution
• Configurable step count, blur pass count, and early-exit transmittance threshold scale from mobile/VR to high-end desktop from a single Volume Profile
• Temporal accumulation reduces the sample count needed for stable results at low resolution

Package Contents

• +12 C# scripts (render feature, render pass, Volume component, custom editor, local light/volume components)
• 4 shaders, 10 HLSL includes (raymarch, temporal reprojection, bilateral blur/upsample, shadow sampling, density noise, depth utilities)
• Fully commented source, no third-party dependencies or paid packages required

Platform Support

• Desktop and console platforms
• Mobile and VR supported via Quarter resolution + aggressive step count presets

Bring AAA-Grade Atmosphere to Your URP Game

Volumetric fog is one of the defining visual signatures of modern AAA titles think the drifting haze of The Witcher 3's swamps or the smoke-choked corridors of Dead Space. The technique behind that look low-resolution raymarching stabilized by temporal reprojection is exactly what powers BT-Spectral Fog, rebuilt from the ground up for URP and Unity 6's Render Graph.

No brute-forcing every pixel. No choosing between "looks good" and "runs well." Spectral Fog raymarches at a fraction of your screen resolution and reconstructs full-quality atmosphere through a temporal and depth-aware pipeline, the same category of trick the big studios rely on, running comfortably on hardware they never had to think about.

🎯 Core Rendering Systems

QuadMarch — Quarter-Res Raymarch Engine

• Raymarches at quarter (or half) resolution instead of full screen, cutting the raw cost of volumetric lighting dramatically
• Transmittance-based early exit skips samples the eye would never notice anyway
• Every knob — resolution, step count, blur passes, lives on the Volume Profile, no code changes needed

GhostGuard — Temporal Stabilization

• Motion-vector reprojection rebuilds detail the low-res march alone can't capture
• Neighborhood clamping kills ghosting on fast camera turns and disocclusion, no smeary trails behind moving objects
• Screen-edge fade removes the seam artifact that plagues naive reprojection

EdgeWeave — Depth-Aware Blur & Upsample

• Smooths noise without smearing fog across silhouette edges
• Thin foreground objects stay crisp against distant fog instead of bleeding into it

🌫 Lighting & Atmosphere

Sun & Local Light Scattering

• Directional light shafts through fog with full shadow and anisotropy control
• Point and spot lights scatter through the volume too, drop a component on any light and it just works
• Adaptive Probe Volume support lets ambient GI color the fog naturally (Unity 2023.1+)

PocketFog — Local Fog Volumes

• Drop box or sphere volumes anywhere for a foggy cave mouth, a swamp patch, a magic mist, independent of the global height fog
• Frustum-culled automatically, so scenes with dozens of pockets don't pay for the ones off-screen

Animated Density Noise

• Wind-driven turbulence breaks the flat "gradient fog" look into something that actually reads as volumetric

🛠 Built for Real Production, Not Just Demos

HeightSync — One-Click Auto Fit

• No more guessing world-space Y values for every new scene. One button reads your terrain and level geometry and sets the fog's floor and ceiling for you.
• The single biggest time-sink with height fog, solved in one click.

Clean Tabbed Inspector

• General, Lighting, and Quality split into tabs instead of one endless list of sliders

Dual Render Path

• Full Unity 6 Render Graph support, with a Compatibility Mode path for URP 2022.3+ same feature set, either way

🎮 Runs Everywhere URP Does

• Scales from VR/mobile presets to full desktop fidelity from a single profile
• Perspective and orthographic cameras both fully supported

What You Get

• Complete, commented source code, nothing obfuscated, nothing locked behind a black box
• Full documentation covering every parameter