block4.glsl

// ... obtain old and new pixel values as before

// compute the color of the old pixel
vec4 colorA = computeColor(
  pixelFloatValueA,
  colorScaleA,
  sentinelValuesA,
  colorScaleLengthA,
  sentinelValuesLengthA
);

// compute the color of the new pixel
vec4 colorB = computeColor(
  pixelFloatValueB,
  colorScaleB,
  sentinelValuesB,
  colorScaleLengthB,
  sentinelValuesLengthB
);

// interpolate between the colors
gl_FragColor = mix(colorA, colorB, interpolationFraction);