Full screen stuck pixel fixer, inspired by http://www.jscreenfix.com.

StuckPixelFix.cs

using System;
using System.Collections.Concurrent;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using Timer=System.Windows.Forms.Timer;

/// <summary>
/// Based on the idea of http://www.jscreenfix.com
/// </summary>
public sealed partial class StuckPixelFixForm : Form
{
    [DllImport("user32.dll")]
    static extern bool LockWindowUpdate(IntPtr hWndLock);

    static readonly BlockingCollection<Bitmap> drawQ = new BlockingCollection<Bitmap>(2);
    static readonly ThreadLocal<RndPixelFiller> filler = new ThreadLocal<RndPixelFiller>(() => new RndPixelFiller());      

    static readonly Timer timer = new Timer { Interval = 10 };
    static TimeStats stats = new TimeStats();
    static ulong framesDisplayed = 0;

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        
        //base.TopMost = true;
        base.DoubleBuffered = true;
        base.FormBorderStyle = FormBorderStyle.None;
        base.WindowState = FormWindowState.Maximized;

        new Thread(RunFramesRenderer) { IsBackground = true }.Start();
        //Task.Factory.StartNew(RunFramesRenderer, TaskCreationOptions.LongRunning);

        timer.Tick += OnTimerTick;
        timer.Start();
    }

    protected override void OnActivated(EventArgs e)
    {
        Cursor.Hide();
        timer.Start();
    }

    protected override void OnDeactivate(EventArgs e)
    {
        Cursor.Show();
        timer.Stop();
    }

    protected override void OnClosed(EventArgs e)
    {
        base.OnClosed(e);
        
        const string f1 = @"ss\.fffff";
        MessageBox.Show(this,
            string.Join(Environment.NewLine,
                "Frame rendering times:",
                "Avg (s) = " + stats.Avg.ToString(f1),
                "Min (s) = " + stats.Min.ToString(f1),
                "Max (s) = " + stats.Max.ToString(f1),
                string.Empty,
                "Frames Per Second (FPS):",
                "Avg = " + (1.0d / stats.Avg.TotalSeconds).ToString("F3"),
                "Min = " + (1.0d / stats.Max.TotalSeconds).ToString("F3"),
                "Max = " + (1.0d / stats.Min.TotalSeconds).ToString("F3"),
                string.Empty,
                "Summary:",
                "App run time = " + (DateTime.UtcNow - Process.GetCurrentProcess().StartTime.ToUniversalTime()),
                "Total frames rendered = " + stats.SamplesCount,
                "Total frames displayed = " + framesDisplayed
                ), Application.ProductName);
    }

    protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
    {
        if (keyData == (Keys.Escape))
        {
            Close();
            return true;
        }
        return base.ProcessCmdKey(ref msg, keyData);
    }

    protected override void OnPaintBackground(PaintEventArgs e)
    {
        if (drawQ.TryTake(out Bitmap frame))
        {
            e.Graphics.DrawImageUnscaled(frame, e.ClipRectangle);
            ++framesDisplayed;
        }
    }

    void OnTimerTick(object sender, EventArgs e)
    {
        LockWindowUpdate(Handle);
        this.Refresh();
        LockWindowUpdate(IntPtr.Zero);
    }

    void RunFramesRenderer()
    {
        var poolLength = drawQ.BoundedCapacity + 2;
        var framesPool = Enumerable.Range(0, poolLength)
            .Select(_ => new Bitmap(Width, Height)).ToArray();
        var frameIndex = 0;
        while (true)
        {
            drawQ.Add(RenderFrame(framesPool[frameIndex]));
            frameIndex = (frameIndex + 1) % poolLength;
        }
    }

    static Bitmap RenderFrame(Bitmap img)
    {
        var data = img.LockBits(new Rectangle(0, 0, img.Width, img.Height),
            ImageLockMode.WriteOnly,
            PixelFormat.Format32bppArgb);
        try
        {
            stats.BeginSample();
#if true // MT
            FillNoiseMT(data);
#else
            FillNoiseST(data);
#endif
            stats.EndSample();
        }
        finally
        {
            img.UnlockBits(data);
        }
        return img;
    }

    static void FillNoiseST(BitmapData data)
    {
        filler.Value.FillBuffer(data.Scan0, data.Scan0 + data.Stride * data.Height);   
    }

    static void FillNoiseMT(BitmapData data)
    {
        var partitioner = Partitioner.Create(0, data.Height);
        Parallel.ForEach(partitioner, (range, state) => 
            filler.Value.FillBuffer(data.Scan0 + data.Stride * range.Item1, data.Scan0 + data.Stride * range.Item2)
        );
    }
}

// Adapted version of fast XorShift
// https://bitbucket.org/rstarkov/demoxorshift/src/tip/Xorshift.cs?fileviewer=file-view-default
sealed class RndPixelFiller
{
    static readonly uint[] pixels = Enumerable
        .Range(0, 8 /* (2 ^ 3) RGB combinations */)
        .Select(MaskToArgb).ToArray();

    static uint MaskToArgb(int mask)
    {
        return ((mask & 4) == 4 ? 0xffff0000 : 0xff000000) |
               ((mask & 2) == 2 ? 0xff00ff00 : 0xff000000) |
               ((mask & 1) == 1 ? 0xff0000ff : 0xff000000);
    }

    uint _x = 123456789;
    uint _y = 362436069;
    uint _z = 521288629;
    uint _w = 88675123;

    public unsafe void FillBuffer(IntPtr start, IntPtr end)
    {
        uint* pbuf = (uint*)start;
        uint* pend = (uint*)end;

        uint* pendQuads = (pend - (pend - pbuf) % 4);
        while (pbuf < pendQuads)
        {
            uint tx = _x ^ (_x << 11);
            uint ty = _y ^ (_y << 11);
            uint tz = _z ^ (_z << 11);
            uint tw = _w ^ (_w << 11);
            *(pbuf++) = pixels[(_x = _w ^ (_w >> 19) ^ (tx ^ (tx >> 8))) % 8];
            *(pbuf++) = pixels[(_y = _x ^ (_x >> 19) ^ (ty ^ (ty >> 8))) % 8];
            *(pbuf++) = pixels[(_z = _y ^ (_y >> 19) ^ (tz ^ (tz >> 8))) % 8];
            *(pbuf++) = pixels[(_w = _z ^ (_z >> 19) ^ (tw ^ (tw >> 8))) % 8];
        }

        if (pbuf < pend)
        {
            uint t = _x ^ (_x << 11);
            _x = _y; _y = _z; _z = _w;
            t = _w = _w ^ (_w >> 19) ^ (t ^ (t >> 8));

            while (true)
            {
                *(pbuf++) = pixels[(t & 0xFF) % 8];
                if (pbuf == pend) break;
                t >>= 8;
            }
        }
    }
    
    /*public static unsafe void TestFill()
    {
        var b = new uint[7];
        fixed (uint* pb = b)
        {
            var p = new IntPtr(pb);
            new RndPixelFiller()
                .FillBuffer(p, IntPtr.Add(p, b.Length * sizeof(uint)));
        }
    }*/
}

[DebuggerDisplay("Avg = {Avg}, Max = {Max}, Min = {Min}, Cnt = {SamplesCount}")]
public sealed class TimeStats
{
    private readonly Stopwatch _stopwatch = Stopwatch.StartNew();

    public TimeSpan Max { get; private set; }
    public TimeSpan Min { get; private set; }
    public TimeSpan Avg { get; private set; }
    public long SamplesCount { get; private set; }

    public void BeginSample()
    {
        _stopwatch.Restart();
    }

    public TimeSpan EndSample()
    {
        var sample = _stopwatch.Elapsed;
        AddSample(sample);
        return sample;
    }

    public void Combine(TimeStats that)
    {
        if (that.SamplesCount == 0)
        {
            return;
        }
        if (this.SamplesCount == 0)
        {
            this.Max = that.Max;
            this.Min = that.Min;
            this.Avg = that.Avg;
            this.SamplesCount = that.SamplesCount;
        }
        else
        {
            var totalSamplesCount = this.SamplesCount + that.SamplesCount;
            this.Max = TimeSpan.FromTicks(Math.Max(this.Max.Ticks, that.Max.Ticks));
            this.Min = TimeSpan.FromTicks(Math.Min(this.Min.Ticks, that.Min.Ticks));
            this.Avg = TimeSpan.FromTicks((long)
                    (this.Avg.Ticks * ((double)this.SamplesCount / totalSamplesCount)
                    + that.Avg.Ticks * ((double)that.SamplesCount / totalSamplesCount))
                );
            this.SamplesCount = totalSamplesCount;
        }
    }

    public static TimeStats operator +(TimeStats stats1, TimeStats stats2)
    {
        var combinedStats = new TimeStats();
        combinedStats.Combine(stats1);
        combinedStats.Combine(stats2);
        return combinedStats;
    }

    public void AddSample(TimeSpan sample)
    {
        var samplesCount = ++SamplesCount;
        if (samplesCount == 1)
        {
            Max = sample;
            Min = sample;
            Avg = sample;
        }
        else
        {
            Max = TimeSpan.FromTicks(Math.Max(Max.Ticks, sample.Ticks));
            Min = TimeSpan.FromTicks(Math.Min(Min.Ticks, sample.Ticks));
            Avg = TimeSpan.FromTicks((Avg.Ticks * (samplesCount - 1) + sample.Ticks) / samplesCount);
        }
    }
}

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new StuckPixelFixForm());
    }
}

In case this helps people in the future, here is a great guide on getting this working:

https://www.reddit.com/r/csharp/comments/rw1320/comment/hr8z2f8/?utm_source=share&utm_medium=web2x&context=3

I can confirm it looks exactly like JScreenFix, but the pattern fills the whole screen.