plasma_derivative_interpolation.js

// stores whether we're interpolating colors
// from palette 0 -> 1 (1) or 1 -> 0 (-1)
let prevDirection = 1;

const updatePalette = t => {
  const timeScale = 0.0005;
  const x = t * timeScale;

  // normalized value 0..1 used to interpolate palette colors
  const inter = (Math.cos(x) + 1) / 2;

  // did we switch direction, and should ergo pick a new palette
  // random palette to interpolate towards?

  const direction = -Math.sin(x) >= 0 ? 1 : -1;
  if (prevDirection != direction) {
    prevDirection = direction;
    if (direction == -1) {
      palettes[0] = makeRandomPalette();
    } else {
      palettes[1] = makeRandomPalette();
    }
  }

  // create interpolated palette for current frame
  for (let i = 0; i < 256; i++) {
    palette[i] = interpolate(palettes[0][i], palettes[1][i], inter);
  }
};