CODEWITHSUNDEEP
c#winforms
dimitris93
dimitris93

Reputation: 4273

Draw filled rectangle on transparent form

I have a form with opacity set to 0. How would I be able to paint a filled rectangle inside that form, that is 50% transparent ?

//brush1 transparency is set at 128 (50%)
SolidBrush brush1 = new SolidBrush(Color.FromArgb(128, 100, 100, 100));

private void Form1_Paint(object sender, PaintEventArgs e)
{
    e.Grapics.FillRectangle(brush1, rectangle1);
}

If I paint using e.Graphics,nothing is drawn on the screen, since the form's opacity is 0.

I tried drawing using Graphics g = Graphics.FromHwnd(IntPtr.Zero); but it is so slow (only slow with brushes with transparency), that is absolutely ineffective.

Edit: I am doing this to draw to the screen. The form is being used a transparent canvas in order to achieve that. I tried using BackColor = Color.LightGreen; TransparencyKey = Color.LightGreen; but that just draws the rectangle LightGreen.

This is what I want to achieve:

1

Upvotes: 0

Views: 2362

Answers (1)

Abdul Saleem
Abdul Saleem

Reputation: 10622

You can achieve this by using two forms. One with a partial opacity on the background and other with Transparency key on the foreground.

enter image description here

The transparent Window is in a Label kept on a form named Foreground_Form. And the background is a form named Form_TransparentBack

Form_TransparentBack

public partial class Form_TransparentBack : Form
{
    public Form_TransparentBack(Form _foregroundForm)
    {
        InitializeComponent();
        StartPosition = _foregroundForm.StartPosition;
        Location = _foregroundForm.Location;
        Size = _foregroundForm.Size;
        _foregroundForm.Resize += _foregroundForm_Resize;
        FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
        _foregroundForm.LocationChanged += _foregroundForm_LocationChanged;
        ShowInTaskbar = false;
        BackColor = Color.WhiteSmoke;
        Opacity = 0.5;
        Timer timer = new Timer() { Interval = 10};
        timer.Tick += delegate(object sn, EventArgs ea)
        {
            (sn as Timer).Stop();
            _foregroundForm.ShowDialog();
        };
        timer.Start();
        Show();
    }

    void _foregroundForm_LocationChanged(object sender, EventArgs e)
    {
        Location = (sender as Form).Location;
    }

    void _foregroundForm_Resize(object sender, EventArgs e)
    {
        WindowState = (sender as Form).WindowState;
        Size = (sender as Form).Size;
    }
}

Foreground_Form

public partial class Foreground_Form : Form
{
    public Foreground_Form()
    {
        InitializeComponent();
        FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;  // required
        TransparencyKey = this.BackColor;  // required
        StartPosition = FormStartPosition.CenterScreen;
        this.Paint += Foreground_Form_Paint;
    }

    void Foreground_Form_Paint(object sender, PaintEventArgs e)
    {
        //this is for the Stroke
        e.Graphics.DrawRectangle(Pens.White, new Rectangle(0, 0, Width - 1, Height - 1));
    }
}

Now you can call any form with the transparent background. For the transparency, you should set the TransparencyKey to the form to be displayed.

private void button1_Click(object sender, EventArgs e)
{
    new Form_TransparentBack(new Foreground_Form());
}

Upvotes: 1

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