PixiEditor/src/ChunkyImageLib/DataHolders/ColorBounds.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using ComputeSharp;
using SkiaSharp;

namespace ChunkyImageLib.DataHolders;

public struct ColorBounds
{
    public float LowerR { get; set; }
    public float LowerG { get; set; }
    public float LowerB { get; set; }
    public float LowerA { get; set; }
    public float UpperR { get; set; }
    public float UpperG { get; set; }
    public float UpperB { get; set; }
    public float UpperA { get; set; }

    public ColorBounds(SKColor color)
    {
        static (float lower, float upper) FindInclusiveBoundaryPremul(byte channel, float alpha)
        {
            float subHalf = channel > 0 ? channel - .5f : channel;
            float addHalf = channel < 255 ? channel + .5f : channel;
            return (subHalf * alpha / 255f, addHalf * alpha / 255f);
        }

        static (float lower, float upper) FindInclusiveBoundary(byte channel)
        {
            float subHalf = channel > 0 ? channel - .5f : channel;
            float addHalf = channel < 255 ? channel + .5f : channel;
            return (subHalf / 255f, addHalf / 255f);
        }

        float a = color.Alpha / 255f;

        (LowerR, UpperR) = FindInclusiveBoundaryPremul(color.Red, a);
        (LowerG, UpperG) = FindInclusiveBoundaryPremul(color.Green, a);
        (LowerB, UpperB) = FindInclusiveBoundaryPremul(color.Blue, a);
        (LowerA, UpperA) = FindInclusiveBoundary(color.Alpha);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public unsafe bool IsWithinBounds(Half* pixel)
    {
        float r = (float)pixel[0];
        float g = (float)pixel[1];
        float b = (float)pixel[2];
        float a = (float)pixel[3];
        if (r < LowerR || r > UpperR)
            return false;
        if (g < LowerG || g > UpperG)
            return false;
        if (b < LowerB || b > UpperB)
            return false;
        if (a < LowerA || a > UpperA)
            return false;
        return true;
    }
    
    [ShaderMethod]
    public readonly bool IsWithinBounds(float4 color)
    {
        float r = color.R;
        float g = color.G;
        float b = color.B;
        float a = color.A;
        if (r < LowerR || r > UpperR)
            return false;
        if (g < LowerG || g > UpperG)
            return false;
        if (b < LowerB || b > UpperB)
            return false;
        return !(a < LowerA) && !(a > UpperA);
    }
}