Blur BackgroundImage in Windows Forms

BlurWindowsForms.cs

using System.Drawing;
using System.Drawing.Imaging;
using BlurBackground;
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namespace Project1
{
    public partial class Form1 : Form
    {
        private PictureBox pb = new PictureBox();

        public Form1()
        {
            InitializeComponent();
        }

        private async void Form1_LoadAsync(object sender, EventArgs e)
        {
            panel1.BackColor = Color.FromArgb(100, 44, 62, 80);
            
            await Task.Delay(500);
                        
            Bitmap bmp = Screenshot.TakeSnapshot(panel1);
            BitmapFilter.GaussianBlur(bmp, 4);

            pb.Image = bmp;
            pb.Dock = DockStyle.Fill;
            pb.BringToFront();
            panel1.Controls.Add(pb);
        }

    }

}



namespace BlurBackground
{
    public class BitmapFilter
    {
        private static bool Conv3x3(Bitmap b, ConvMatrix m)
        {
            // Avoid divide by zero errors
            if (0 == m.Factor) return false;

            Bitmap bSrc = (Bitmap)b.Clone();

            // GDI+ still lies to us - the return format is BGR, NOT RGB.
            BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            BitmapData bmSrc = bSrc.LockBits(new Rectangle(0, 0, bSrc.Width, bSrc.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int stride = bmData.Stride;
            int stride2 = stride * 2;
            System.IntPtr Scan0 = bmData.Scan0;
            System.IntPtr SrcScan0 = bmSrc.Scan0;

            unsafe
            {
                byte* p = (byte*)(void*)Scan0;
                byte* pSrc = (byte*)(void*)SrcScan0;

                int nOffset = stride + 6 - b.Width * 3;
                int nWidth = b.Width - 2;
                int nHeight = b.Height - 2;

                int nPixel;

                for (int y = 0; y < nHeight; ++y)
                {
                    for (int x = 0; x < nWidth; ++x)
                    {
                        nPixel = ((((pSrc[2] * m.TopLeft) + (pSrc[5] * m.TopMid) + (pSrc[8] * m.TopRight) +
                            (pSrc[2 + stride] * m.MidLeft) + (pSrc[5 + stride] * m.Pixel) + (pSrc[8 + stride] * m.MidRight) +
                            (pSrc[2 + stride2] * m.BottomLeft) + (pSrc[5 + stride2] * m.BottomMid) + (pSrc[8 + stride2] * m.BottomRight)) / m.Factor) + m.Offset);

                        if (nPixel < 0) nPixel = 0;
                        if (nPixel > 255) nPixel = 255;

                        p[5 + stride] = (byte)nPixel;

                        nPixel = ((((pSrc[1] * m.TopLeft) + (pSrc[4] * m.TopMid) + (pSrc[7] * m.TopRight) +
                            (pSrc[1 + stride] * m.MidLeft) + (pSrc[4 + stride] * m.Pixel) + (pSrc[7 + stride] * m.MidRight) +
                            (pSrc[1 + stride2] * m.BottomLeft) + (pSrc[4 + stride2] * m.BottomMid) + (pSrc[7 + stride2] * m.BottomRight)) / m.Factor) + m.Offset);

                        if (nPixel < 0) nPixel = 0;
                        if (nPixel > 255) nPixel = 255;

                        p[4 + stride] = (byte)nPixel;

                        nPixel = ((((pSrc[0] * m.TopLeft) + (pSrc[3] * m.TopMid) + (pSrc[6] * m.TopRight) +
                            (pSrc[0 + stride] * m.MidLeft) + (pSrc[3 + stride] * m.Pixel) + (pSrc[6 + stride] * m.MidRight) +
                            (pSrc[0 + stride2] * m.BottomLeft) + (pSrc[3 + stride2] * m.BottomMid) + (pSrc[6 + stride2] * m.BottomRight)) / m.Factor) + m.Offset);

                        if (nPixel < 0) nPixel = 0;
                        if (nPixel > 255) nPixel = 255;

                        p[3 + stride] = (byte)nPixel;

                        p += 3;
                        pSrc += 3;
                    }

                    p += nOffset;
                    pSrc += nOffset;
                }
            }

            b.UnlockBits(bmData);
            bSrc.UnlockBits(bmSrc);

            return true;
        }

        public static bool GaussianBlur(Bitmap b, int nWeight /* default to 4*/)
        {
            ConvMatrix m = new ConvMatrix();
            m.SetAll(1);
            m.Pixel = nWeight;
            m.TopMid = m.MidLeft = m.MidRight = m.BottomMid = 2;
            m.Factor = nWeight + 12;

            return BitmapFilter.Conv3x3(b, m);
        }
        
    }
    
    
     public class ConvMatrix
    {
        public int TopLeft = 0, TopMid = 0, TopRight = 0;
        public int MidLeft = 0, Pixel = 1, MidRight = 0;
        public int BottomLeft = 0, BottomMid = 0, BottomRight = 0;
        public int Factor = 1;
        public int Offset = 0;
        public void SetAll(int nVal)
        {
            TopLeft = TopMid = TopRight = MidLeft = Pixel = MidRight = BottomLeft = BottomMid = BottomRight = nVal;
        }
    }
    
    
    public class Screenshot
    {
        public static Bitmap TakeSnapshot(Control ctl)
        {
            Bitmap bmp = new Bitmap(ctl.Size.Width, ctl.Size.Height);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);
            g.CopyFromScreen(ctl.PointToScreen(ctl.ClientRectangle.Location), new Point(0, 0), ctl.ClientRectangle.Size);
            return bmp;
        }
    }
    
}