Catalog/MaddoShared.ImageSharpTests/Helpers/PixelInspector.cs

using System;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;

namespace MaddoShared.ImageSharpTests.Helpers
{
    public static class PixelInspector
    {
        public static int CountNonBackgroundPixels(string path, int x, int y, int width, int height, Rgba32 background, int tolerance = 0)
        {
            using var img = SixLabors.ImageSharp.Image.Load<Rgba32>(path);
            var bx = Math.Max(0, x);
            var by = Math.Max(0, y);
            var bw = Math.Min(width, img.Width - bx);
            var bh = Math.Min(height, img.Height - by);
            if (bw <= 0 || bh <= 0) return 0;

            int count = 0;
            img.ProcessPixelRows(accessor =>
            {
                for (int yy = by; yy < by + bh; yy++)
                {
                    var row = accessor.GetRowSpan(yy);
                    for (int xx = bx; xx < bx + bw; xx++)
                    {
                        var p = row[xx];
                        if (!IsApproximatelyEqual(p, background, tolerance)) count++;
                    }
                }
            });

            return count;
        }

        private static bool IsApproximatelyEqual(Rgba32 a, Rgba32 b, int tol)
        {
            return Math.Abs(a.R - b.R) <= tol && Math.Abs(a.G - b.G) <= tol && Math.Abs(a.B - b.B) <= tol && Math.Abs(a.A - b.A) <= tol;
        }
    }
}