Turbo Colormap Polynomial Approximation in GLSL

turbo_colormap.glsl

// Copyright 2019 Google LLC.
// SPDX-License-Identifier: Apache-2.0

// Polynomial approximation in GLSL for the Turbo colormap
// Original LUT: https://gist.github.com/mikhailov-work/ee72ba4191942acecc03fe6da94fc73f

// Authors:
//   Colormap Design: Anton Mikhailov ([email protected])
//   GLSL Approximation: Ruofei Du ([email protected])

vec3 TurboColormap(in float x) {
  const vec4 kRedVec4 = vec4(0.13572138, 4.61539260, -42.66032258, 132.13108234);
  const vec4 kGreenVec4 = vec4(0.09140261, 2.19418839, 4.84296658, -14.18503333);
  const vec4 kBlueVec4 = vec4(0.10667330, 12.64194608, -60.58204836, 110.36276771);
  const vec2 kRedVec2 = vec2(-152.94239396, 59.28637943);
  const vec2 kGreenVec2 = vec2(4.27729857, 2.82956604);
  const vec2 kBlueVec2 = vec2(-89.90310912, 27.34824973);
  
  x = saturate(x);
  vec4 v4 = vec4( 1.0, x, x * x, x * x * x);
  vec2 v2 = v4.zw * v4.z;
  return vec3(
    dot(v4, kRedVec4)   + dot(v2, kRedVec2),
    dot(v4, kGreenVec4) + dot(v2, kGreenVec2),
    dot(v4, kBlueVec4)  + dot(v2, kBlueVec2)
  );
}