Faux Lighting Simulation (Metal + SwiftUI Shader)

A lightweight “fake flashlight” / spotlight effect written as a SwiftUI stitchable Metal shader.
It renders an expanding cone beam from a fixed source point, adds chromatic dispersion (RGB splitting), a soft halo/glow, and finishes with a tone-mapping pass so highlights feel bright without blowing out.

fauxlightsim.mp4

Parameters

• intensity — overall brightness of the beam
• disperse — cone spread and chromatic separation strength
• rotation — beam direction (radians), relative to “down”
• radius — starting beam width at the source

Implementation notes

• sdSegmentSim(p, a, b) returns:
  • distance from p to the segment axis
  • t = clamped projection along the segment in [0, 1]
• Beam profile uses:
  • beam = 1 - smoothstep(0, width, dist)
  • then softened with pow(beam, softness)
• Chromatic dispersion uses a perpendicular vector to the beam direction:
  • perp = (-dir.y, dir.x)
  • offset positions drive R and B channel separation.

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Why it’s “faux”

This is not true volumetric lighting (no geometry occlusion, scattering volumes, or shadows).
It’s a fast UI-friendly illusion built from distance fields + tuned falloffs that reads like a flashlight beam.