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

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 a

Answer 1

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);
        }
    }
}