Transparent images with C# WinForms

Question

I am working on a Windows Forms application in VS 2008, and I want to display one image over the top of another, with the top image being a gif or something with transparent parts.

Basically I have a big image and I want to put a little image on top if it, so that they kinda appear as one image to the user.

I've been trying to use a picturebox, but this doesn't seem to have worked, any suggestions?

Answer 1

Put the big/bottom image on a PictureBox, then add a handler to the OnPaint event and use one of the e.Graphics.DrawImage() overloads. You can load the image using Image.FromFile().

The small/top image will have to have an alpha channel and be transparent in the background for the overlay to work. You should be able to ensure this pretty easily in Photoshop or something similar. Make sure you save in a format that supports the alpha channel, such as PNG.

Answer 2

I've always found that I've had to composite the images myself, using a single picturebox or control. Having two pictureboxes with transparent parts has never worked for me.

Answer 3

Duplicate question answered here (same applies to C#)-

http://stackoverflow.com/questions/394426/how-vbnet-handles-image-transparency-with-images-thatre-on-top-of-each-other#394478

http://stackoverflow.com/questions/392257/transparency-for-images-in-visual-basic-net#392264

Answer 4

I was in a similar situation a couple of days ago. You can create a transparent control to host your image.

public class TransparentControl : Control
{
    private readonly Timer refresher;
    private Image _image;

    public TransparentControl()
    {
        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        BackColor = Color.Transparent;
        refresher = new Timer();
        refresher.Tick += TimerOnTick;
        refresher.Interval = 50;
        refresher.Enabled = true;
        refresher.Start();
    }

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

    protected override void OnMove(EventArgs e)
    {
        RecreateHandle();
    }


    protected override void OnPaint(PaintEventArgs e)
    {
        if (_image != null)
        {
            e.Graphics.DrawImage(_image, (Width / 2) - (_image.Width / 2), (Height / 2) - (_image.Height / 2));
        }
    }

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

    //Hack
    public void Redraw()
    {
        RecreateHandle();
    }

    private void TimerOnTick(object source, EventArgs e)
    {
        RecreateHandle();
        refresher.Stop();
    }

    public Image Image
    {
        get
        {
            return _image;
        }
        set
        {
            _image = value;
            RecreateHandle();
        }
    }
}