Reasons for why a WinForms label does not want to

Question

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...

Answer 1

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.

Answer 2

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.

Answer 3

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);
        }
    }
}

Answer 4

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.

Answer 5

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 :)

Answer 6

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

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