Question

I am having trouble getting my Form background image to display correctly with a gradient transparency. That is, the edge of the image (or anywhere for that matter) has a fading or non-255 Alpha value. The result is that everywhere the Alpha is NOT 255 (or 0 – I can’t remember) I see my background color. Here is a screen shot:

What I have in this setup is a 24bit bmp file with a green background that I’m trying to key out via the Form.TransparencyKey property:

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);

    Color key = ((Bitmap)this.BackgroundImage).GetPixel(0, 0);
    this.TransparencyKey = key;
}

I have also tried setting the Form’s BackColor property to the same key value but that did not make a difference.

I also tried saving my image as a png with transparency and keying out the entire form background but that didn’t work either.

I know this is possible somehow, I’ve seen applications like Photoshop use this for a decade. I’m on WinXP Pro if that matters.

Anyone have experience with this and have an idea what step I’m missing or doing incorrectly?

Answer 1

The WinForms implementation of Form only permits a solid colour to be used as the transparency key. It’s not possible to have varying levels of transparency.

Most apps with splash screens like yours take a screenshot of the desktop (within the bounds that their splash screen will occupy) and then composite their splash screen on top of this screenshot. They then display the resulting bitmap to the user, giving the impression of an alpha gradient.