C#

Imports System.Drawing
Imports System.Drawing.Drawing2D

Public Class TransPanelForm
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call
        Me.SetStyle(ControlStyles.AllPaintingInWmPaint Or ControlStyles.DoubleBuffer Or ControlStyles.UserPaint, True)
    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents Panel1 As System.Windows.Forms.Label
    Friend WithEvents Panel2 As System.Windows.Forms.Label
    Friend WithEvents Panel3 As System.Windows.Forms.Label
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Panel1 = New System.Windows.Forms.Label
        Me.Panel3 = New System.Windows.Forms.Label
        Me.Panel3.SuspendLayout()
        Me.SuspendLayout()
        '
        'Panel1
        '
        Me.Panel1.BackColor = System.Drawing.Color.Transparent
        Me.Panel1.Dock = System.Windows.Forms.DockStyle.Fill
        Me.Panel1.Location = New System.Drawing.Point(0, 0)
        Me.Panel1.Name = "Panel1"
        Me.Panel1.Size = New System.Drawing.Size(270, 244)
        Me.Panel1.TabIndex = 0
        '
        'Panel3
        '
        Me.Panel3.BackColor = System.Drawing.Color.Transparent
        Me.Panel3.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle
        Me.Panel3.Controls.Add(Me.Panel1)
        Me.Panel3.Dock = System.Windows.Forms.DockStyle.Fill
        Me.Panel3.Location = New System.Drawing.Point(10, 10)
        Me.Panel3.Name = "Panel3"
        Me.Panel3.Size = New System.Drawing.Size(272, 246)
        Me.Panel3.TabIndex = 0
        '
        'TransPanelForm
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.Panel3)
        Me.DockPadding.All = 10
        Me.Name = "TransPanelForm"
        Me.Text = "TransPanelForm"
        Me.Panel3.ResumeLayout(False)
        Me.ResumeLayout(False)

    End Sub

#End Region

    ''' <summary>The current rectangle that is dragged.</summary>
    Private DragRect As Rectangle
    ''' <summary>A collection of rectangles.</summary>
    Private FinalRects As New ArrayList

    ''' <summary>The position at which the mouse was pressed.</summary>
    Private MouseDownPos As Point
    ''' <summary>Is the left mouse button down?</summary>
    Private LeftMouseDown As Boolean

    Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
        MyBase.OnPaintBackground(e)

        Dim rect As Rectangle = Me.ClientRectangle
        Dim brush As New LinearGradientBrush(rect, Color.White, Color.LightSteelBlue, LinearGradientMode.ForwardDiagonal)
        e.Graphics.FillRectangle(brush, rect)
        brush.Dispose()

    End Sub
    Protected Overrides Sub OnSizeChanged(ByVal e As System.EventArgs)
        MyBase.OnSizeChanged(e)
        Me.Invalidate()
    End Sub

    ''' <summary>Calculates the DragRect.</summary>
    Private Function CalcDragRect(ByVal mouseX As Integer, ByVal mouseY As Integer) As Rectangle
        Return Rectangle.FromLTRB(Math.Min(mouseX, MouseDownPos.X), _
                                  Math.Min(mouseY, MouseDownPos.Y), _
                                  Math.Max(mouseX, MouseDownPos.X), _
                                  Math.Max(mouseY, MouseDownPos.Y))
    End Function

#Region " Panel1_Mouse... "

    Private Sub Panel1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseDown
        If e.Button = MouseButtons.Left Then
            Debug.WriteLine("Panel1_MouseDown")
            MouseDownPos = New Point(e.X, e.Y)
            LeftMouseDown = True
            DragRect = New Rectangle(e.X, e.Y, 0, 0)
            Panel2.Invalidate()
        End If
    End Sub

    Private Sub Panel1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseUp
        If LeftMouseDown Then
            Debug.WriteLine("Panel1_MouseUp")
            LeftMouseDown = False
            DragRect = Me.CalcDragRect(e.X, e.Y)
            Panel2.Invalidate()
            FinalRects.Add(DragRect)
        End If
    End Sub

    Private Sub Panel1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseMove
        If e.Button = MouseButtons.Left Then
            Debug.WriteLine("Panel1_MouseMove")
            DragRect = Me.CalcDragRect(e.X, e.Y)
            Panel1.Invalidate()
        End If
    End Sub

#End Region

    ''' <summary>Draws a rectangle.</summary>
    ''' <remarks>Instead of just doing 'g.DrawRectangle(pen, rect)', 
    '''          this method draws a line if the width and/or height
    '''          of the rectangle is zero. This way a line is drawn, 
    '''          instead of just nothing.</remarks>
    Public Shared Sub DrawRect(ByVal g As Graphics, ByVal rect As Rectangle, ByVal pen As Pen)
        If (rect.Width = 0) AndAlso (rect.Height = 0) Then
            g.DrawLine(pen, rect.X, rect.Y, rect.X, rect.Y + 0.01!)
        ElseIf (rect.Width > 0) AndAlso (rect.Height = 0) Then
            g.DrawLine(pen, rect.X, rect.Y, rect.Right, rect.Y)
        ElseIf (rect.Width = 0) AndAlso (rect.Height > 0) Then
            g.DrawLine(pen, rect.X, rect.Y, rect.X, rect.Bottom)
        Else '(rect.Width > 0) AndAlso (rect.Height > 0)
            g.DrawRectangle(pen, rect)
        End If
    End Sub

    Private Sub Panel2_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel2.Paint
        For Each rect As Rectangle In FinalRects
            DrawRect(e.Graphics, rect, Pens.Red)
        Next
    End Sub
    Private Sub Panel1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel1.Paint
        If LeftMouseDown Then
            Dim pen As New Pen(Color.Blue)
            pen.DashStyle = DashStyle.Dash
            DrawRect(e.Graphics, DragRect, pen)
            pen.Dispose()
        End If
    End Sub

End Class

namespace TransparentPanels
{
    using System;
    using System.Collections;
    using System.ComponentModel;
    using System.Diagnostics;
    using System.Drawing;
    using System.Drawing.Drawing2D;
    using System.Runtime.CompilerServices;
    using System.Windows.Forms;

    public class TransPanelForm : Form
    {
        // Methods
        public TransPanelForm()
        {
            this.FinalRects = new ArrayList();
            this.InitializeComponent();
            this.SetStyle(ControlStyles.DoubleBuffer | 
                         (ControlStyles.AllPaintingInWmPaint | 
                          ControlStyles.UserPaint), true);
        }

        private Rectangle CalcDragRect(int mouseX, int mouseY)
        {
            return Rectangle.FromLTRB(Math.Min(mouseX, this.MouseDownPos.X), 
                                      Math.Min(mouseY, this.MouseDownPos.Y), 
                                      Math.Max(mouseX, this.MouseDownPos.X), 
                                      Math.Max(mouseY, this.MouseDownPos.Y));
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing && (this.components != null))
            {
                this.components.Dispose();
            }
            base.Dispose(disposing);
        }

        public static void DrawRect(Graphics g, Rectangle rect, Pen pen)
        {
            if ((rect.Width == 0) && (rect.Height == 0))
            {
                g.DrawLine(pen, (float)rect.X, (float)rect.Y, 
                                (float)rect.X, (float)(rect.Y + 0.01f));
            }
            else if ((rect.Width > 0) && (rect.Height == 0))
            {
                g.DrawLine(pen, rect.X, rect.Y, rect.Right, rect.Y);
            }
            else if ((rect.Width == 0) && (rect.Height > 0))
            {
                g.DrawLine(pen, rect.X, rect.Y, rect.X, rect.Bottom);
            }
            else
            {
                g.DrawRectangle(pen, rect);
            }
        }

        [DebuggerStepThrough]
        private void InitializeComponent()
        {
            this.Panel1 = new Label();
            this.Panel2 = new Label();
            this.SuspendLayout();
            this.Panel1.BackColor = Color.Transparent;
            this.Panel1.BorderStyle = BorderStyle.FixedSingle;
            this.Panel1.Dock = DockStyle.Left;
            Point point1 = new Point(10, 10);
            this.Panel1.Location = point1;
            this.Panel1.Name = "Panel1";
            Size size1 = new Size(270, 0x10a);
            this.Panel1.Size = size1;
            this.Panel1.TabIndex = 0;
            this.Panel2.BackColor = Color.Transparent;
            this.Panel2.BorderStyle = BorderStyle.FixedSingle;
            this.Panel2.Dock = DockStyle.Right;
            point1 = new Point(290, 10);
            this.Panel2.Location = point1;
            this.Panel2.Name = "Panel2";
            size1 = new Size(0x110, 0x10a);
            this.Panel2.Size = size1;
            this.Panel2.TabIndex = 0;
            size1 = new Size(5, 13);
            this.AutoScaleBaseSize = size1;
            size1 = new Size(0x23c, 0x11e);
            this.ClientSize = size1;
            this.Controls.Add(this.Panel2);
            this.Controls.Add(this.Panel1);
            this.DockPadding.All = 10;
            this.Name = "TransPanelForm";
            this.Text = "TransPanelForm";
            this.ResumeLayout(false);
        }

        [STAThread]
        public static void Main()
        {
            Application.Run(new TransPanelForm());
        }

        protected override void OnPaintBackground(PaintEventArgs e)
        {
            base.OnPaintBackground(e);
            Rectangle rectangle1 = this.ClientRectangle;
            LinearGradientBrush brush1 = new LinearGradientBrush(rectangle1, 
                                         Color.White, Color.LightSteelBlue, 
                                         LinearGradientMode.ForwardDiagonal);
            e.Graphics.FillRectangle(brush1, rectangle1);
            brush1.Dispose();
        }

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

        private void Panel1_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                Point point1 = new Point(e.X, e.Y);
                this.MouseDownPos = point1;
                this.LeftMouseDown = true;
                Rectangle rectangle1 = new Rectangle(e.X, e.Y, 0, 0);
                this.DragRect = rectangle1;
                this.Panel2.Invalidate();
            }
        }

        private void Panel1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                this.DragRect = this.CalcDragRect(e.X, e.Y);
                this.Panel1.Invalidate();
            }
        }

        private void Panel1_MouseUp(object sender, MouseEventArgs e)
        {
            if (this.LeftMouseDown)
            {
                this.LeftMouseDown = false;
                this.DragRect = this.CalcDragRect(e.X, e.Y);
                this.Panel2.Invalidate();
                this.FinalRects.Add(this.DragRect);
            }
        }

        private void Panel1_Paint(object sender, PaintEventArgs e)
        {
            if (this.LeftMouseDown)
            {
                Pen pen1 = new Pen(Color.Blue);
                pen1.DashStyle = DashStyle.Dash;
                TransPanelForm.DrawRect(e.Graphics, this.DragRect, pen1);
                pen1.Dispose();
            }
        }

        private void Panel2_Paint(object sender, PaintEventArgs e)
        {
            IEnumerator enum1;
            try
            {
                enum1 = this.FinalRects.GetEnumerator();
                while (enum1.MoveNext())
                {
                    Rectangle rectangle1 = (Rectangle) enum1.Current;
                    TransPanelForm.DrawRect(e.Graphics, rectangle1, Pens.Red);
                }
            }
            finally
            {
             }
        }

        // Properties
        internal virtual Label Panel1
        {
            get
            {
                return this._Panel1;
            }
            [MethodImpl(MethodImplOptions.Synchronized)]
            set
            {
                if (this._Panel1 != null)
                {
                    this._Panel1.Paint -= new PaintEventHandler(this.Panel1_Paint);
                    this._Panel1.MouseMove -= new MouseEventHandler(this.Panel1_MouseMove);
                    this._Panel1.MouseUp -= new MouseEventHandler(this.Panel1_MouseUp);
                    this._Panel1.MouseDown -= new MouseEventHandler(this.Panel1_MouseDown);
                }
                this._Panel1 = value;
                if (this._Panel1 != null)
                {
                    this._Panel1.Paint += new PaintEventHandler(this.Panel1_Paint);
                    this._Panel1.MouseMove += new MouseEventHandler(this.Panel1_MouseMove);
                    this._Panel1.MouseUp += new MouseEventHandler(this.Panel1_MouseUp);
                    this._Panel1.MouseDown += new MouseEventHandler(this.Panel1_MouseDown);
                }
            }
        }

        internal virtual Label Panel2
        {
            get
            {
                return this._Panel2;
            }
            [MethodImpl(MethodImplOptions.Synchronized)]
            set
            {
                if (this._Panel2 != null)
                {
                    this._Panel2.Paint -= new PaintEventHandler(this.Panel2_Paint);
                }
                this._Panel2 = value;
                if (this._Panel2 != null)
                {
                    this._Panel2.Paint += new PaintEventHandler(this.Panel2_Paint);
                }
            }
        }

        // Fields
        [AccessedThroughProperty("Panel1")]
        private Label _Panel1;
        [AccessedThroughProperty("Panel2")]
        private Label _Panel2;
        private IContainer components;
        private Rectangle DragRect;
        private ArrayList FinalRects;
        private bool LeftMouseDown;
        private Point MouseDownPos;
    }
}