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Medium Nature

Rainbow arc

A seven-band rainbow arching over a pale sky.

Play this challenge All challenges

The target picture for the shader challenge "Rainbow arc" — Recreate this picture. You pass at a 99% match, then try to write it in fewer characters than the par.

How this challenge works

You write a fragment shader that draws the picture above, live in your browser. A match bar shows how close you are, and the score combines accuracy, code size (the par is 423 characters in Unity (Built-in)) and GPU speed. Work in HLSL, GLSL, WGSL, Metal or Godot and export the result when you are done.

The numbers you need

Arc center: float2(0.0, -0.3)
t: (distance - 0.3) / 0.3 → band if 0..1, and only above p.y > -0.3
Bands: floor(t * 7.0) / 7.0
Band color: 0.5 + 0.5 * cos(6.28318 * (band + float3(0.0, 0.33, 0.67)))
Sky: lerp(float3(0.55,0.78,1.0), float3(0.85,0.93,1.0), 1.0 - uv.y)

Solve it in your language

Unity (Built-in), Unity (URP), Unreal, Shadertoy / WebGL, OpenGL (LWJGL, raylib), three.js, GameMaker, LÖVE (Lua), Godot, Apple (iOS, macOS), WebGPU / Bevy.