Transparent Control on Transparent control?

Question

I created a TransparentTableLayoutPanel:

class TransTablePanel : TableLayoutPanel
{
    public TransTablePanel()
    {

    }

    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.
    }
}

And a transparent PictureBox (I tried just using BackColor = Transparent and it didn't work)

class TransPicBox : PictureBox
{
    public TransPicBox()
    {

    }

    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.
    }
}

Here is the result:

enter image description here

First cell is the PictureBox with this paint event:

private void picBoxCompass_Paint(object sender, PaintEventArgs e)
    {
        Bitmap b = Properties.Resources.Compass_Rose;
        float rot = PitControl.GetPitbullRotation();
        e.Graphics.DrawImage(rotateImage(b, rot), 0, 0, picBoxCompass.Width, picBoxCompass.Height);
        e.Graphics.DrawLine(LinePen, picBoxCompass.Width / 2, 0, picBoxCompass.Width / 2, picBoxCompass.Height / 2);
        e.Graphics.FillPie(Brushes.Green, picBoxCompass.Width / 2 - 10, picBoxCompass.Height / 2 - 10, 20, 20, 0, 360);
    }

And you can see that is not Transparent (Black Background) and second cell is transparent (you can see my form's background image).

How can i make the PictureBox Transparent ?

I'm not sure, but I think you shoud not override the OnPaintBackground Methods, if you specify transparency as background, you will have to draw it — Tokk, Oct 24 '11 at 11:43
@Tokk I tried using a normal PictureBox with Transparent Background as well without success, and the TranPanel works perfect. (Faster then using Normal Panel with Transparent color) — Danpe, Oct 24 '11 at 12:12

Renatas M. · Accepted Answer · 2011-10-24T16:12:15.377

Ok Iam adding code that worked for me. Its not very nice(I would like to hear how it could be done better), but maybe it will help you

public class TransPicBox : Control
{
    public Image Image
    {
        get;
        set;
    }

    public TransPicBox()
    {
        SetStyle(ControlStyles.AllPaintingInWmPaint |
                 ControlStyles.SupportsTransparentBackColor, true);
        base.BackColor = Color.FromArgb(0, 0, 0, 0);//Added this because image wasnt redrawn when resizing form
    }

    protected override void OnPaintBackground(PaintEventArgs e)
    {

    }

    protected override void OnPaint(PaintEventArgs e)
    {
        if (Image != null)
        {
            e.Graphics.DrawImage(Image, 0, 0, Image.Width, Image.Height);
        }
    }

    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= 0x20;
            return cp;
        }
    }
}

You will need to set Image property.

Edit: Note: Image should be with transparent background (tested with *.png format)

Result:

enter image description here

No flickering in your project when resizing form? When i tested I've got flickering, probably because of hi resolution form background image(image layout style = strech) — Renatas M., Oct 24 '11 at 16:15
I used to get flickering but then i created the TransTablePanel class and now no flickering :) — Danpe, Oct 24 '11 at 21:03

Transparent Control on Transparent control?

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