CODEWITHSUNDEEP
c#winformstransparency
Svish
Svish

Reputation: 158291

Reasons for why a WinForms label does not want to be transparent?

Why can't I set the BackColor of a Label to Transparent? I have done it before, but now it just don't want to...

I created a new UserControl, added a progressbar and a label to it. When I set the BackColor of the label to transparent it is still gray =/ Why is this?

What I wanted was to have the label on top of the progressbar so that its text was "in" the progressbar...

Upvotes: 30

Views: 32802

Answers (11)

BlueRaja - Danny Pflughoeft
BlueRaja - Danny Pflughoeft

Reputation: 86146

Here is a transparent control I wrote a while ago which displays rotated text. Most of the code comes from here, though IIRC I had to make a few tweaks to get it to work.

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Text;
using System.Linq;
using System.Windows.Forms;

namespace MyNamespace
{
    public partial class RotatedText : UserControl
    {
        private readonly Timer _invalidationTimer;
        private const int WS_EX_TRANSPARENT = 0x00000020;

        public RotatedText()
        {
            this.SetStyle(ControlStyles.SupportsTransparentBackColor, true);
            InitializeComponent();

            _invalidationTimer = new Timer {Interval = 500, Enabled = true};
            _invalidationTimer.Tick += TickHandler;
        }

        [Browsable(true)]
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        [Category("Appearance")]
        [Description("Text which appears in control")]
        public string Text { get; set; }

        #region Transparent background
        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= WS_EX_TRANSPARENT;
                return cp;
            }
        }

        private void TickHandler(object sender, EventArgs e)
        {
            InvalidateEx();
        }

        private void InvalidateEx()
        {
            if (Parent != null)
                Parent.Invalidate(Bounds, false);
            else
                Invalidate();
        }

        protected override void OnPaintBackground(PaintEventArgs e)
        {
            //Intentionally do nothing - stops background from drawing
            //base.OnPaintBackground(e);
        } 
        #endregion

        //Rotate text and draw
        protected override void OnPaint(PaintEventArgs e)
        {
            double angleRadians = Math.Atan2(Height, Width);
            float angleDegrees = -1*(float) (angleRadians*180/Math.PI);
            angleDegrees *= 0.9f;
            e.Graphics.RotateTransform(angleDegrees, MatrixOrder.Append);
            e.Graphics.TranslateTransform(20, Height - 75, MatrixOrder.Append);
            e.Graphics.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;
            Font font = new Font("Ariel", 50);
            e.Graphics.DrawString(Text, font, Brushes.Gray, 1, 2); //Shadow
            e.Graphics.DrawString(Text, font, Brushes.Red, 0, 0);
        }
    }
}

Upvotes: 1

Elvedin Hamzagic
Elvedin Hamzagic

Reputation: 855

This is a very simple solution and works great:

public class MyLabel : Label
{
    private bool fTransparent = false;
    public bool Transparent
    {
        get { return fTransparent; }
        set { fTransparent = value; }
    }
    public MyLabel() : base()
    {
    }
    protected override CreateParams CreateParams
    {
        get
        {
            if (fTransparent)
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT
                return cp;
            }
            else return base.CreateParams;
        }
    }
    protected override void WndProc(ref Message m)
    {
        if (fTransparent)
        {
            if (m.Msg != 0x14 /*WM_ERASEBKGND*/ && m.Msg != 0x0F /*WM_PAINT*/)
                base.WndProc(ref m);
            else 
            {
                if (m.Msg == 0x0F) // WM_PAINT
                    base.OnPaint(new PaintEventArgs(Graphics.FromHwnd(Handle), ClientRectangle));
                DefWndProc(ref m);
            }
        }
        else base.WndProc(ref m);
    }
}

When label backcolor is transparent, then label only takes picture of its underlying control the first time when it is created, after that label backcolor is constant. And each time when label repaints itself, it repaints to that fixed color or pattern.

Overriding CreateParams affects on how window for control will be created, this enables real transparency.

Overriding WndProc you control which messages should be passed to base class. We must filtrate WM_ERASEBKGND and WM_PAINT, but we also have to trigger paint event.

Upvotes: 3

truthseeker
truthseeker

Reputation: 1256

Most simple solution is following:

  1. Set background color to transparency either in visual editor or in constructor of your form:

    this.label1.BackColor = System.Drawing.Color.Transparent;

  2. Set Parent property of your label to control that you want to be visible behind the text. This can be done in form constructor or in Load method:

    this.label1.Parent = progressBar1;

Its true that this is not true transparency as in DirectX. The result you see on display is composed only from two layers. You cant sum up more than two layers with this approach (each layer having its own transparency defined by alpha parameter). But its suitable for many practical situations you can encounter in Winforms programming.

Upvotes: 9

alexander willemse
alexander willemse

Reputation: 59

Use a LinkLabel not a normal Label 

    private void MakeTransparentLabel(System.Windows.Forms.LinkLabel LinkLabel)
    {
        this.MakeTransparentLabel(LinkLabel, Color.White);
    }
    private void MakeTransparentLabel(System.Windows.Forms.LinkLabel LinkLabel, Color ForeColor)
    {
        LinkLabel.ForeColor = ForeColor;
        LinkLabel.LinkColor = ForeColor;
        LinkLabel.VisitedLinkColor = ForeColor;
        LinkLabel.ActiveLinkColor = ForeColor;
        LinkLabel.DisabledLinkColor = ForeColor;
        LinkLabel.LinkArea = new LinkArea(0, 0);
        LinkLabel.LinkBehavior = LinkBehavior.NeverUnderline;
        LinkLabel.Cursor = Cursors.Arrow;
        LinkLabel.BackColor = Color.Transparent;
    }
    private void SetTransparentLabelText(System.Windows.Forms.LinkLabel LinkLabel, string Text)
    {
        if (string.IsNullOrEmpty(Text)) { LinkLabel.Text = " "; return; }
        LinkLabel.Text = Text;
    }

Upvotes: 5

Steve
Steve

Reputation: 7

Select BackColor, go the Web tab, and select Transparent. Generates the following.

        this.label1.BackColor = System.Drawing.Color.Transparent;

Upvotes: -3

lincolnk
lincolnk

Reputation: 11238

as to an explanation for your problem, windows doesn't do transparency for background controls like you'd expect-i'm guessing the gray background is actually the form's surface. whatever controls are drawn between the form surface and your label are ignored.

Upvotes: 0

Maciek Talaska
Maciek Talaska

Reputation: 1638

It is possible to do exactly what you want to achieve. It just takes a little time to play with controls. It is possible to create a Label control with transparent background, and place it on top of Progressbar control.

Check my answer to another SO question.

Upvotes: 0

Hans Passant
Hans Passant

Reputation: 942256

Add a new class to your project and post the code shown below. Build. Drop the new control from the top of the toolbox onto your form.

using System;
using System.Windows.Forms;

public class TransparentLabel : Label {
  public TransparentLabel() {
    this.SetStyle(ControlStyles.Opaque, true);
    this.SetStyle(ControlStyles.OptimizedDoubleBuffer, false);
  }
  protected override CreateParams CreateParams {
    get {
      CreateParams parms = base.CreateParams;
      parms.ExStyle |= 0x20;  // Turn on WS_EX_TRANSPARENT
      return parms;
    }
  }
}

Upvotes: 32

thmsn
thmsn

Reputation: 1996

So as the comment to my previous answer stated, Control is the default behaviour, and is what I remembered as being Transparent.

Anyway, have you tried setting the background property of your UserControl, or the container your label is in (Panel, Form, whatever?), your label should reflect that color :)

Old Answer: Its been a while since I did winforms programming, but as I recall labels are transparent per default? thus its only the text that gets an actual color and the bacground color mimics whatever is behind it :)

Upvotes: 0

はると
はると

Reputation: 1499

If you want to focus on designing your windows application, I suggest you use WPF.

Making controles transparent in WPF is very easy.

<TextBox Width="200" Height="40" Opacity="0.5"/>

Upvotes: 1

Rune Grimstad
Rune Grimstad

Reputation: 36340

WinForms doesn't really support transparent controls, but you can make a transparent control yourself. See my answer here.

In your case you should probably subclass the progress bar and override the OnPaint method to draw a text on the progress bar.

Upvotes: 14

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