Transparent background on winforms?

46
votes

I wanted to make my windows form transparent so removed the borders, controls and everything leaving only the forms box, then I tried to the BackColor and TransparencyKey to transparent but it didnt work out as BackColor would not accept transparent color. After searching around I found this at msdn:

SetStyle(ControlStyles.UserPaint, true);
SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
SetStyle(ControlStyles.SupportsTransparentBackColor, true);
this.BackColor = Color.Transparent;
this.TransparencyKey = BackColor;

Unhappyly it did not work either. I still get the grey or any other selected color background.

All I wanted to do is to have the windows form transparent so I could use a background image that would act as if it was my windows form.

I searched around here and saw many topics in regards opacity which is not what I am looking for and also saw some in regards this method I was trying but have not found an answer yet.

Hope anyone can light my path.

UPDATE:

image removed as problem is solved

8
c#winformsbackgroundtransparent
Can you please clarify a little what you want to do? I didn't understand what you are trying to achieve with the background image. – Ran
I want to make my own custom application window in a simple way so instead of using the winforms default window, I am trying to make it transparent to use my background image instead. – Prix
Do you mean that the background image will be drawn on some other window that is placed behind your window? I don't understand why you can't just override OnPaint and draw the background image there... – Ran
@Ran I have updated with an example, the green part is remaints of the windows form which i want to make completely transparent. – Prix
I see. So 2 more questions...:) Did you set the image file as the Form's BackgroundImage property? What is the image's format? – Ran

8 Answers

82
votes

The manner I have used before is to use a wild color (a color no one in their right mind would use) for the BackColor and then set the transparency key to that.

this.BackColor = Color.LimeGreen;
this.TransparencyKey = Color.LimeGreen;
28
votes

A simple solution to get a transparent background in a windows form is to overwrite the OnPaintBackground method like this:

protected override void OnPaintBackground(PaintEventArgs e)
{
    //empty implementation
}

(Notice that the base.OnpaintBackground(e) is removed from the function)

8
votes

I've tried the solutions above (and also) many other solutions from other posts.

In my case, I did it with the following setup:

public partial class WaitingDialog : Form
{
    public WaitingDialog()
    {
        InitializeComponent();

        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        this.BackColor = Color.Transparent;

        // Other stuff
    }

    protected override void OnPaintBackground(PaintEventArgs e) { /* Ignore */ }
}

As you can see, this is a mix of previously given answers.

7
votes

Here was my solution:

In the constructors add these two lines:

this.BackColor = Color.LimeGreen;
this.TransparencyKey = Color.LimeGreen;

In your form, add this method:

protected override void OnPaintBackground(PaintEventArgs e)
{
    e.Graphics.FillRectangle(Brushes.LimeGreen, e.ClipRectangle);
}

Be warned, not only is this form fully transparent inside the frame, but you can also click through it. However, it might be cool to draw an image onto it and make the form able to be dragged everywhere to create a custom shaped form.

6
votes

My solution was extremely close to Joel's (Not Etherton, just plain Joel):

public partial class WaitingDialog : Form
{
    public WaitingDialog()
    {
        InitializeComponent();

        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        this.BackColor = Color.Transparent;
        this.TransparencyKey = Color.Transparent; // I had to add this to get it to work.

        // Other stuff
    }

    protected override void OnPaintBackground(PaintEventArgs e) { /* Ignore */ }
}
2
votes

What works for me is using a specific color instead of the real ability of .png to represent transparency.

So, what you can do is take your background image, and paint the transparent area with a specific color (Magenta always seemed appropriate to me...).

Set the image as the Form's BackgrounImage property, and set the color as the Form's TransparencyKey. No need for changes in the Control's style, and no need for BackColor.

I've tryed it right now and it worked for me...

2
votes

I tried almost all of this. but still couldn't work. Finally I found it was because of 24bitmap problems. If you tried some bitmap which less than 24bit. Most of those above methods should work.

2
votes

I had drawn a splash screen (32bpp BGRA) with "transparent" background color in VS2013 and put a pictureBox in a form for display. For me a combination of above answers worked:

public Form1()
{
    InitializeComponent();

    SetStyle(ControlStyles.SupportsTransparentBackColor, true);
    this.BackColor = this.pictureBox1.BackColor;
    this.TransparencyKey = this.pictureBox1.BackColor;
}

So make sure you use the same BackColor everywhere and set that color as the TransparencyKey.