Based on my previous question (

I wish it to have transparent background, i.e. to not draw the gray border on top of the black background.

Can I do it with my TransparentButton class, without major changes (like drawing the text and background, and border manually)?

CodePudding user response：

Why are you setting WS_EX_TRANSPARENT in CreateParams? When I need a transparent background, I don't use WinAPI constants. WinForms was created to simplify the usage, and the solution I know is to set the BackgroundColor of your button to Color.Transparent.

Yes, it just sets the background color same as the parent's background color, but it works.

CodePudding user response：

This edited TransparentButton improves on my previous answer. It no longer requires an override to OnPaint and uses no custom drawing whatsoever. What I missed the first time is to simply set the Button.BackgroundImage to the camouflage bitmap.

Requirements:

• Create a button with transparent background.
• Do it without drawing the background manually in OnPaint.
• Keep the Button.FlatStyle as FlatStyle.Standard.
• Do not disturb the rounded edges of the standard button.

class TransparentButton : Button
{
    protected override void OnSizeChanged(EventArgs e)
    {
        base.OnSizeChanged(e);
        Refresh();
    }
    public void SetParentForm(Form form)
    {
        _parentForm= form;
        Refresh();
    }
    Form? _parentForm = null;
    public new void Refresh()
    {
        if (!(DesignMode || _parentForm == null))
        {
            // Hide this button before drawing
            Visible = false;

            // Draw the full container
            var tmp = (Bitmap)new Bitmap(_parentForm.Width, _parentForm.Height);
            _parentForm.DrawToBitmap(tmp, new Rectangle(0, 0, _parentForm.Width, _parentForm.Height));
            var ptScreen = _parentForm.PointToScreen(_parentForm.ClientRectangle.Location);
            var ptOffset = new Point(
                ptScreen.X - _parentForm.Location.X,
                ptScreen.Y - _parentForm.Location.Y);

            var clipBounds = new Rectangle(Location.X   ptOffset.X, Location.Y   ptOffset.Y, Width, Height);
            BackgroundImage = tmp.Clone(
                clipBounds, 
                System.Drawing.Imaging.PixelFormat.DontCare);

            // Show this button.
            Visible = true;
        }
    }

Design Mode Example

Main form BackgroundImage to main form with a Stretch layout. Then overlay a TableLayoutPanel whose job it is to keep the button scaled correctly as the form resizes. TransparentButton is now placed in one of the cells.

Test

Here's the code I used to test this answer:

public partial class MainForm : Form
{
    public MainForm() => InitializeComponent();       
    protected override void onl oad(EventArgs e)
    {
        base.OnLoad(e);
        buttonTransparent.FlatStyle= FlatStyle.Standard;
        buttonTransparent.SetParentForm(this);
        buttonTransparent.ForeColor= Color.White;
        buttonTransparent.Click  = onClickTransparent;
    }
    private void onClickTransparent(object? sender, EventArgs e) =>
        MessageBox.Show("Clicked!");
    protected override CreateParams CreateParams
    {
        get
        {
            const int WS_EX_COMPOSITED = 0x02000000;
            // https://stackoverflow.com/a/36352503/5438626
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= WS_EX_COMPOSITED;
            return cp;
        }
    }
}