C# transparent background for window form

Question

I've already seen Transparent background on winforms?

it doesnt offer solution to my problem. I am using the same method to try to achieve transparency

    public Form1()
    {
        this.SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        InitializeComponent();
        this.BackColor = Color.FromArgb(0, 0, 0, 0);
    }

But this gives a grey background, not transparent. How can I get an actually transparent background (note, transparency key solutions do not give a transparent background, and when I paint with alpha channel less than 255, it blends with the set form background colour, and not the actual background)? I want to paint to certain regions of the screen with alpha < 255 and blend with the background (not the form).

Answer 1

The way I did it long time ago was to find an unused color for the form background and then set the transparency key to it:

this.BackColor = Color.Magenta;
this.TransparencyKey = Color.Magenta;

Other ways are:

• Creating a background image, painting the transparent area of it with a specific color and setting it as the form BackgroundImage... then setting the TransparencyKey to that color.
• Overriding OnPaintBackground method with an empty method.

[EDIT] As Mario states, normally the default transparent color for the key is Magenta.

Answer 2

This is the best way to make the transparent background of winform.

right after this:

public partial class frmTransparentBackcolor : Form
{
    public frmTransparentBackcolor()
    {
        InitializeComponent();
        //set the backcolor and transparencykey on same color.
        this.BackColor = Color.LimeGreen;
        this.TransparencyKey = Color.LimeGreen;
    }
    protected override void OnPaintBackground(PaintEventArgs e)
    {
        e.Graphics.FillRectangle(Brushes.LimeGreen, e.ClipRectangle);
    }
}

hope this will help.