semi-transparent form but opaque Controls in C#

Question

How to make semi transparent form in C# windows form application

I have tried the TransparentKey which makes it full-transparent. and tried Opacity but it effects the whole form (with controls).

I want only form part to be semi-transparent but not Controls.

Gingery

Answer 1

You can use a hatch brush with a certain percentage, for example:

    using System.Drawing.Drawing2D;

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        var hb = new HatchBrush(HatchStyle.Percent50, this.TransparencyKey);

        e.Graphics.FillRectangle(hb,this.DisplayRectangle);
    }

Neurotomy

Oh my. The result is disgusting. Sorry, but it truly is. – Burack

Answer 2

I found the Hatch Brush grotesque,

Instead of:

protected override void OnPaintBackground(PaintEventArgs e) {
  var hb = new HatchBrush(HatchStyle.Percent80, this.TransparencyKey);
  e.Graphics.FillRectangle(hb, this.DisplayRectangle);
}

I used:

protected override void OnPaintBackground(PaintEventArgs e) {
  var sb = new SolidBrush(Color.FromArgb(100, 100, 100, 100));
  e.Graphics.FillRectangle(sb, this.DisplayRectangle);
}

Navaho

Perfect, your answer was the only one that served me – Mecklenburg

Is it for WPF cause I am not able to find the event as OnPaintBackground in windows forms – Maidservant

Yes, this WPF not winforms. why use winforms when you can use wpf? – Navaho

Answer 3

There is a solution which add semi-transparency to a Control (not Form) :

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        // Apply opacity (0 to 255)
        panel1.BackColor = Color.FromArgb(25, panel1.BackColor);
    }

In visual Studio : (alpha activated only during execution)

Executed on Windows 7 :

Executed on an old WIndows 2003 Server :

Source : https://mcmap.net/q/271559/-how-can-i-set-the-opacity-or-transparency-of-a-panel-in-winforms

Talented

The form is not semi-transparent in your example..., or do I miss something? – Ruelu

Maybe the background is so much uniform and it is not enough clear but it really works with alpha channel. If you watch closely you will see the shading :) – Talented

I have tested and have the following result: The button1 is opaque, the panel1 is semi transparent, the form1 is opaque. You can not see, what is behind the form, but the question was about a semi-transparent form. So I have the same problem, but your answere seems to be not correct... – Ruelu

I see what you mean, you're true. In facts I've answered for a Control but the question is about the Form... I will update – Talented

Who has upvoted this question, just after I have downvoted it? This answere should be deleted, because it leads people into the wrong direction. – Ruelu

I tried this, and it thrown an ArgumentException with the message that the control does not support transparent background colors. – Isobar