BlendOperations.cs

using System;
using UnityEngine;

namespace BetterContinents;

public static class BlendOperations
{
    // https://photoshoptrainingchannel.com/blending-modes-explained/
    public enum BlendModeType
    {
        Normal, // Overwrite (still respecting mask)

        // Darken modes
        Darken, // Min
        Multiply,
        ColorBurn,
        LinearBurn,

        // Lighten modes
        Lighten, // Max
        Screen,
        ColorDodge,
        LinearDodge, // Add

        // Contrasting modes
        Overlay,
        HardLight,
        SoftLight,
        VividLight,
        LinearLight,
        PinLight,
        HardMix,

        // Inversion modes
        Difference,
        Exclusion,
        Subtract,
        Divide,
    }

    // http://www.simplefilter.de/en/basics/mixmods.html -- this has a and b the wrong way around
    // http://www.deepskycolors.com/archive/2010/04/21/formulas-for-Photoshop-blending-modes.html
    // https://en.wikipedia.org/wiki/Blend_modes
    // https://photoblogstop.com/photoshop/photoshop-blend-modes-explained

    /// <summary>
    /// 
    /// </summary>
    /// <param name="a">Bottom layer</param>
    /// <param name="b">Top layer</param>
    /// <param name="mode"></param>
    /// <returns></returns>
    /// <exception cref="ArgumentOutOfRangeException"></exception>
    public static float Blend(float a, float b, BlendModeType mode)
    {
        switch (mode)
        {
            case BlendModeType.Normal: return b;
            case BlendModeType.Darken: return Mathf.Min(a, b);
            case BlendModeType.Multiply: return a * b;
            case BlendModeType.ColorBurn: return 1f - (1f - a) / b;
            case BlendModeType.LinearBurn: return a + b - 1f;
            case BlendModeType.Lighten: return Mathf.Max(a, b);
            case BlendModeType.Screen: return 1f - (1f - a) * (1f - b);
            case BlendModeType.ColorDodge: return a / (1f - b);
            case BlendModeType.LinearDodge: return a + b;
            case BlendModeType.Overlay: return a > 0.5f ? 1f - 2f * (1f - a) * (1f - b) : 2f * a * b;
            case BlendModeType.HardLight: return b > 0.5f ? 1f - 2f * (1f - a) * (1f - b) : 2f * a * b;
            case BlendModeType.SoftLight: return (1f - 2f * b) * a * a + 2f * b * a; // Pegtop's formula
            case BlendModeType.VividLight: return b > 0.5f ? a / (2f * (1f - b)) : 1f - (1f - a) / (2f * b);
            case BlendModeType.LinearLight: return a + 2f * b - 1f;
            case BlendModeType.PinLight: return a < 2f * b - 1f ? 2f * b - 1f : a > 2f * b ? 2f * b : a;
            case BlendModeType.HardMix: return b < 1f - a ? 0f : 1f;
            case BlendModeType.Difference: return Mathf.Abs(a - b);
            case BlendModeType.Exclusion: return a + b - 2f * a * b;
            case BlendModeType.Subtract: return a - b;
            case BlendModeType.Divide: return a / b;
            default:
                throw new ArgumentOutOfRangeException(nameof(mode), mode, null);
        }
    }
}