ShanXi_SmartControl/IntelligentControlForsx/MyControls/TransparentPanel.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace IntelligentControlForsx.MyControls
{
    public class TransparentPanel : Panel
    {
        public TransparentPanel()
        {
            SetStyle(ControlStyles.SupportsTransparentBackColor
                    | ControlStyles.Opaque,
                        true);
            BackColor = Color.Transparent;
        }

        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                /* Window extended styles 
    #define WS_EX_DLGMODALFRAME    0x00000001L
    #define WS_EX_DRAGDETECT       0x00000002L
    #define WS_EX_NOPARENTNOTIFY   0x00000004L
    #define WS_EX_TOPMOST          0x00000008L
    #define WS_EX_ACCEPTFILES      0x00000010L
    #define WS_EX_TRANSPARENT      0x00000020L*/
                cp.ExStyle = cp.ExStyle | 0x20;
                return cp;
            }
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            if (BackColor != Color.Transparent)
            {
                var bounds = new Rectangle(0, 0, Width - 1, Height - 1);
                //const int alpha = 165;

                using (var bckColor = new SolidBrush(Color.FromArgb(_alpha, BackColor)))
                {
                    e.Graphics.FillRectangle(bckColor, bounds);
                }
            }
            base.OnPaint(e);
        }

        protected override void OnBackColorChanged(EventArgs e)
        {
            Parent.Invalidate(this.Bounds, true);
            base.OnBackColorChanged(e);
        }

        protected override void OnParentBackColorChanged(EventArgs e)
        {
            Invalidate();
            base.OnParentBackColorChanged(e);
        }

        private int _alpha = 168;

        [Browsable(true), Category("Data")]
        public int Alpha
        {
            get
            {
                return _alpha;
            }
            set
            {
                _alpha = value;
                this.Invalidate();
            }
        }
    }

}