How to clear a transparent panel?

Question

I made a transparent panel like this (in C#) :

public class TransparentPanel : Panel
{
    public TransparentPanel()
    {
    }

    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams createParams = base.CreateParams;
            createParams.ExStyle |= 0x00000020; // WS_EX_TRANSPARENT
            return createParams;
        }
    }

    protected override void OnPaintBackground(PaintEventArgs e)
    {
        // Do not paint background.
    }
}

It is displayed over a normal Panel. I want to draw a circle to show something in the other panel, so I draw my circle on the transparent 's OnPaint method. Then, I want to show something else, so I need this circle to "move" somewhere else.

But I can't.

None of the solutions I could find here worked for me, though I do draw this circle in the OnPaint method. I do not use the Graphics object of the event, because if I do, nothing is displayed at all.

So, I have to use this:

this.CreateGraphics()

I can't draw another circle over it, using the background color : my background needs to stay transparent. And drawing a circle with Color.Transparent doesn't work.

Clearing the transparent panel results in a black background replacing the transparent one.

The instruction

Graphics.Clear();

doesn't compile.

Neither does this one :

gr.Clear();

because it needs a Color parameter.

And this:

gr.Clear(Color.transparent);

creates a black background.

Seems to me I have tried everything I could think of.

Any idea ?

score 1 · Answer 1 · answered Jan 23 '13 at 19:09

1

I had a similar problem in Java and could resove it by repainting the parent panel. This cleared the transparent child panel as well.

answered Jan 23 '13 at 19:09

Runo

31
2

How to clear a transparent panel?

1 Answers1