Question Transparent Panel disappears when clicking

[mbz]

Hey guys,

I've got a big problem, which many people seems to have:


I'm developing a WinForms application which contains a PDF editor. The class containing the AciveXControl is called PdfControl.
The PdfControl has a child which is called DrawPanel. Well, the DrawPanel is a transparent panel. On this panel the user can add
a comment (as you can see below)





To provide the transparency, I override the CreateParams and WndProc as follows:

    protected override CreateParams CreateParams
    {
        get
        {
            var cp = base.CreateParams;
            cp.ExStyle |= 0x00000020; //WM_EX_TRANSPARENT
            return cp;
        }
    }
    
    protected override void WndProc(ref Message m)
    {
        switch (m.Msg)
        {
            case 0x84: //WM_NCHITTEST
                m.Result = (IntPtr) HTTRANSPARENT;
                break;


            case 0x0014: // WM_ERASEBKGND
                m.Result = (IntPtr)1;
                break;


            default:
                base.WndProc(ref m);
                break;
        }
    }

Everything is working fine for now. The problem is, when clicking into the Comment (which actually is a Control containing
a RichTextBox, a panel and two buttons) the comment - well, the whole DrawPanel - disappears.
But not for real: the curosr is still there, and if the mouse hovers into that region where the Comment supposed to be, the buttons
are redrawn and visible again.




This is, how it should look like:



When scrolling, the Comment is redrawn and appears constantly - except a kind of flicker during the scroll.


The solution you can find all over the internet when searching for that problem

SetStyle(ControlStyles.DoubleBuffer
            | ControlStyles.AllPaintingInWmPaint
            | ControlStyles.ResizeRedraw
            | ControlStyles.UserPaint, 
            | ControlStyles.SupportsTransparentBackColor
            true);

doesn't work neither.
Hope, you've got a solution for me.


Thanks
mbz