Windows XP Grayscale Shutdown Effect in Windows Forms

• Download source code - 163 KB
• Download demo - 75.7 KB

Introduction

The following code will create a gray scale Windows Shutdown effect for Windows Forms.

Algorithm

1. Create a bitmap image of the Windows form by capturing the screenshot of form.
2. Convert the bitmap into grayscale.
3. Set the background image of a panel control to the grayscale bitmap and set its Dock property to Fill.

Using the code

Create a bitmap image of the Windows form

There is no direct way in .NET to capture a Windows form screen into a bitmap; therefore, we have to use the BitBlt function of gdi32.dll. The BitBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context.

//necessary function to create bitmap of form
[DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
public static extern IntPtr GetDC(IntPtr hWnd);

[DllImport("user32.dll", ExactSpelling = true)]
public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);

[DllImport("gdi32.dll", ExactSpelling = true)]
public static extern IntPtr BitBlt(IntPtr hDestDC, int x, int y, 
       int nWidth, int nHeight, IntPtr hSrcDC, 
       int xSrc, int ySrc, int dwRop);

private Bitmap GetFormImage(Form frm)
{
    //get graphics object of the form
    //pixel of the object will be copied to the bitmap

    Graphics g = frm.CreateGraphics();
    Size s = frm.Size;

    //create blank bitmap of the size of form
    Bitmap formImage = new Bitmap(s.Width, s.Height, g);

    //create graphic object of the bitmap
    //the copied pixel will be transferred to this object
    Graphics mg = Graphics.FromImage(formImage);

    //get handles of the source and destinatio graphics objects
    //this handle will be used in BitBlt function
    IntPtr dc1 = g.GetHdc();
    IntPtr dc2 = mg.GetHdc();

    //here goes the function that will transfer 
    //bits block from form graphics object to bitmap
    BitBlt(dc2, 0, 0, frm.ClientRectangle.Width, 
           frm.ClientRectangle.Height, dc1, 0 , 0 , 13369376);

    g.ReleaseHdc(dc1);
    mg.ReleaseHdc(dc2);
    return formImage;
}

Convert the bitmap into a grayscale bitmap

public static Bitmap MakeGrayscale(Bitmap original)
{
    //make an empty bitmap the same size as original
    Bitmap newBitmap = new Bitmap(original.Width, original.Height);
    for (int i = 0; i < original.Width; i++)
    {
        for (int j = 0; j < original.Height; j++)
        {
            //get the pixel from the original image
            Color originalColor = original.GetPixel(i, j);
            //create the grayscale version of the pixel
            int grayScale = (int)((originalColor.R * .3) + (originalColor.G * .59)
                + (originalColor.B * .11));
            //create the color object
            Color newColor = Color.FromArgb(grayScale, grayScale, grayScale);
            //set the new image's pixel to the grayscale version
            newBitmap.SetPixel(i, j, newColor);
        }
    }
    return newBitmap;
}

Set the background image of a Panel control to the grayscale image and set its Dock property to Fill

private void btnExit_Click(object sender, EventArgs e)
{
    //set the background image of the panel with grey scale form image
    panel1.BackgroundImage = MakeGrayscale(GetFormImage(this));
    panel1.Visible = true;

    //dock this panel to fill the entire form
    panel1.Dock = DockStyle.Fill;

    if (DialogResult.Yes == MessageBox.Show("Do you want to Exit", 
                            "Exit Windows", MessageBoxButtons.YesNo))            
        Application.Exit();
    
    else
    {
        panel1.BackgroundImage = null;
        panel1.Visible = false;
    }
}

Points of interest

My code lacks two things, and with a little effort, this can be improved. I hope to do it in my next update. First, the transition from the color bitmap to the grayscale is done at once. We can produce a gradual transition by setting the background image to intermediate grayscale images. Second, the code runs in a single thread so the message box appear after the transition is done. With a multithreading approach, we can achieve the grayscale transition on a different thread.