调试易

设置Form的TransparencyKey属性，将TextBox的BackColor设置为相同的值。
注意这个颜色应该避开窗体上不应该透明的部分的颜色。表情么？点回复框上方的“管理UBB插件”按钮，加载表情。

◐o◑~~~我照着你说的做了，textbox变成镂空的了不是我FORM的背景图片

而且还出现了一个问题    我是做登陆页面的，窗体加载时，默认焦点在用户名那个textbox    可是我要输入密码的话，我鼠标点一下密码的textbox，因为是镂空的，所以直接切换出去了

给你个正确答案:把下面代码原样复制到你的*.CS文件中.
TextBox类 用  Public.NewTextBox 代替
一切就OK了

namespace Public
{
 public class win32
 {
   
  public const int  WM_MOUSEMOVE      =              0x0200;
  public const int  WM_LBUTTONDOWN     =             0x0201;
  public const int  WM_LBUTTONUP       =             0x0202;
  public const int  WM_RBUTTONDOWN     =             0x0204;
  public const int  WM_LBUTTONDBLCLK   =             0x0203;
  public const int  WM_MOUSELEAVE      =             0x02A3;
  public const int WM_PAINT     =                   0x000F;
  public const int WM_ERASEBKGND   =                0x0014;
  public const int WM_PRINT         =               0x0317;
  public const int WM_HSCROLL       =              0x0114;
  public const int WM_VSCROLL       =              0x0115;
  public const int EM_GETSEL              = 0x00B0;
  public const int EM_LINEINDEX           = 0x00BB;
  public const int EM_LINEFROMCHAR        = 0x00C9;
  public const int EM_POSFROMCHAR         = 0x00D6;  [System.Runtime.InteropServices.DllImport("USER32.DLL", EntryPoint= "PostMessage")]
  public static extern bool PostMessage(IntPtr hwnd, uint msg,
   IntPtr wParam, IntPtr lParam);  // Put this declaration in your class   //IntPtr
  [System.Runtime.InteropServices.DllImport("USER32.DLL", EntryPoint= "SendMessage")]
  public static extern int SendMessage(IntPtr hwnd, int msg, IntPtr wParam,
   IntPtr lParam);
  
  [System.Runtime.InteropServices.DllImport("USER32.DLL", EntryPoint= "GetCaretBlinkTime")]
  public static extern uint GetCaretBlinkTime();
  const int WM_PRINTCLIENT = 0x0318;  const long PRF_CHECKVISIBLE=0x00000001L;
  const long PRF_NONCLIENT = 0x00000002L;
  const long PRF_CLIENT  = 0x00000004L;
  const long PRF_ERASEBKGND = 0x00000008L;
  const long PRF_CHILDREN = 0x00000010L;
  const long PRF_OWNED  = 0x00000020L;  public static bool CaptureWindow(System.Windows.Forms.Control control, ref System.Drawing.Bitmap bitmap)
  {
   //This function captures the contents of a window or control   Graphics g2 = Graphics.FromImage(bitmap);   int meint = (int)(PRF_CLIENT | PRF_ERASEBKGND); //| PRF_OWNED ); //  );
   System.IntPtr meptr = new System.IntPtr(meint);   System.IntPtr hdc = g2.GetHdc();
   win32.SendMessage(control.Handle,win32.WM_PRINT,hdc,meptr);   g2.ReleaseHdc(hdc);
   g2.Dispose();   return true;
   
  }
 }
}

namespace Public
{
    public class NewTextBox : System.Windows.Forms.TextBox
    {
        #region private variables
        private uPictureBox myPictureBox;
        private bool myUpToDate = false;
        private bool myCaretUpToDate = false;
        private Bitmap myBitmap;
        private Bitmap myAlphaBitmap;
        private int myFontHeight = 10;
        private System.Windows.Forms.Timer myTimer1;
        private bool myCaretState = true;
        private bool myPaintedFirstTime = false;
        private Color myBackColor = Color.White;
        private int myBackAlpha = 10;
        private System.ComponentModel.Container components = null;        #endregion // end private variables
        #region public methods and overrides
        public NewTextBox()
        {
            InitializeComponent();
            this.BackColor = myBackColor;
            this.SetStyle(ControlStyles.UserPaint, false);
            this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
            this.SetStyle(ControlStyles.DoubleBuffer, true);
            myPictureBox = new uPictureBox();
            this.Controls.Add(myPictureBox);
            myPictureBox.Dock = DockStyle.Fill;
        }
        protected override void OnResize(EventArgs e)
        {
            base.OnResize(e);
            this.myBitmap = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);//(this.Width,this.Height);
            this.myAlphaBitmap = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);//(this.Width,this.Height);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnKeyDown(KeyEventArgs e)
        {
            base.OnKeyDown(e);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnKeyUp(KeyEventArgs e)
        {
            base.OnKeyUp(e);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);
            this.Invalidate();
        }
        protected override void OnGiveFeedback(GiveFeedbackEventArgs gfbevent)
        {
            base.OnGiveFeedback(gfbevent);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnMouseLeave(EventArgs e)
        {
            Point ptCursor = Cursor.Position;            Form f = this.FindForm();
            ptCursor = f.PointToClient(ptCursor);
            if (!this.Bounds.Contains(ptCursor))
                base.OnMouseLeave(e);
        }
        protected override void OnChangeUICues(UICuesEventArgs e)
        {
            base.OnChangeUICues(e);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void OnGotFocus(EventArgs e)
        {
            base.OnGotFocus(e);
            myCaretUpToDate = false;
            myUpToDate = false;
            this.Invalidate();
            myTimer1 = new System.Windows.Forms.Timer(this.components);
            myTimer1.Interval = (int)win32.GetCaretBlinkTime(); //  usually around 500;            myTimer1.Tick += new EventHandler(myTimer1_Tick);
            myTimer1.Enabled = true;
        }        protected override void OnLostFocus(EventArgs e)
        {
            base.OnLostFocus(e);
            myCaretUpToDate = false;
            myUpToDate = false;
            this.Invalidate();
            myTimer1.Dispose();
        }
        protected override void OnFontChanged(EventArgs e)
        {
            if (this.myPaintedFirstTime)
                this.SetStyle(ControlStyles.UserPaint, false);            base.OnFontChanged(e);            if (this.myPaintedFirstTime)
                this.SetStyle(ControlStyles.UserPaint, true);
            myFontHeight = GetFontHeight();
            myUpToDate = false;
            this.Invalidate();
        }        protected override void OnTextChanged(EventArgs e)
        {
            base.OnTextChanged(e);
            myUpToDate = false;
            this.Invalidate();
        }
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            if (m.Msg == win32.WM_PAINT)
            {
                myPaintedFirstTime = true;
                if (!myUpToDate || !myCaretUpToDate)
                    GetBitmaps();
                myUpToDate = true;
                myCaretUpToDate = true;                if (myPictureBox.Image != null) myPictureBox.Image.Dispose();
                myPictureBox.Image = (Image)myAlphaBitmap.Clone();
            }
            else if (m.Msg == win32.WM_HSCROLL || m.Msg == win32.WM_VSCROLL)
            {
                myUpToDate = false;
                this.Invalidate();
            }            else if (m.Msg == win32.WM_LBUTTONDOWN
             || m.Msg == win32.WM_RBUTTONDOWN
             || m.Msg == win32.WM_LBUTTONDBLCLK
             )
            {
                myUpToDate = false;
                this.Invalidate();
            }            else if (m.Msg == win32.WM_MOUSEMOVE)
            {
                if (m.WParam.ToInt32() != 0)
                {
                    myUpToDate = false;
                    this.Invalidate();
                }
            }
        }

代码太长,提示一次不能太多,回贴不能连续超过三次。你写个邮箱，给你发过去。
把包括下面的代码，共三个贴，合并起来
       protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (components != null)
                {
                    components.Dispose();
                }
            }
            base.Dispose(disposing);
        }        #endregion
        #region public property overrides        public new BorderStyle BorderStyle
        {
            get { return base.BorderStyle; }
            set
            {
                if (this.myPaintedFirstTime)
                    this.SetStyle(ControlStyles.UserPaint, false);                base.BorderStyle = value;                if (this.myPaintedFirstTime)
                    this.SetStyle(ControlStyles.UserPaint, true);                this.myBitmap = null;
                this.myAlphaBitmap = null;
                myUpToDate = false;
                this.Invalidate();
            }
        }        public new Color BackColor
        {
            get
            {
                return Color.FromArgb(base.BackColor.R, base.BackColor.G, base.BackColor.B);
            }
            set
            {
                myBackColor = value;
                base.BackColor = value;
                myUpToDate = false;
            }
        }
        public override bool Multiline
        {
            get { return base.Multiline; }
            set
            {
                if (this.myPaintedFirstTime)
                    this.SetStyle(ControlStyles.UserPaint, false);                base.Multiline = value;                if (this.myPaintedFirstTime)
                    this.SetStyle(ControlStyles.UserPaint, true);                this.myBitmap = null;
                this.myAlphaBitmap = null;
                myUpToDate = false;
                this.Invalidate();
            }
        }
        #endregion    //end public property overrides
        #region private functions and classes        private int GetFontHeight()
        {
            Graphics g = this.CreateGraphics();
            SizeF sf_font = g.MeasureString("X", this.Font);
            g.Dispose();
            return (int)sf_font.Height;
        }
        private void GetBitmaps()
        {            if (myBitmap == null
             || myAlphaBitmap == null
             || myBitmap.Width != Width
             || myBitmap.Height != Height
             || myAlphaBitmap.Width != Width
             || myAlphaBitmap.Height != Height)
            {
                myBitmap = null;
                myAlphaBitmap = null;
            }            if (myBitmap == null)
            {
                myBitmap = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);//(Width,Height);
                myUpToDate = false;
            }
            if (!myUpToDate)
            {
                //Capture the TextBox control window                this.SetStyle(ControlStyles.UserPaint, false);                win32.CaptureWindow(this, ref myBitmap);                this.SetStyle(ControlStyles.UserPaint, true);
                this.SetStyle(ControlStyles.SupportsTransparentBackColor, true);
                this.BackColor = Color.FromArgb(myBackAlpha, myBackColor);            }
            //--            Rectangle r2 = new Rectangle(0, 0, this.ClientRectangle.Width, this.ClientRectangle.Height);
            ImageAttributes tempImageAttr = new ImageAttributes();
            //Found the color map code in the MS Help            ColorMap[] tempColorMap = new ColorMap[1];
            tempColorMap[0] = new ColorMap();
            tempColorMap[0].OldColor = Color.FromArgb(255, myBackColor);
            tempColorMap[0].NewColor = Color.FromArgb(myBackAlpha, myBackColor);            tempImageAttr.SetRemapTable(tempColorMap);            if (myAlphaBitmap != null)
                myAlphaBitmap.Dispose();
            myAlphaBitmap = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);//(Width,Height);            Graphics tempGraphics1 = Graphics.FromImage(myAlphaBitmap);            tempGraphics1.DrawImage(myBitmap, r2, 0, 0, this.ClientRectangle.Width, this.ClientRectangle.Height, GraphicsUnit.Pixel, tempImageAttr);            tempGraphics1.Dispose();            //----            if (this.Focused && (this.SelectionLength == 0))
            {
                Graphics tempGraphics2 = Graphics.FromImage(myAlphaBitmap);
                if (myCaretState)
                {
                    //Draw the caret
                    Point caret = this.findCaret();
                    Pen p = new Pen(this.ForeColor, 3);
                    tempGraphics2.DrawLine(p, caret.X, caret.Y + 0, caret.X, caret.Y + myFontHeight);
                    tempGraphics2.Dispose();
                }            }        }        private Point findCaret()
        {
            Point pointCaret = new Point(0);
            int i_char_loc = this.SelectionStart;
            IntPtr pi_char_loc = new IntPtr(i_char_loc);            int i_point = win32.SendMessage(this.Handle, win32.EM_POSFROMCHAR, pi_char_loc, IntPtr.Zero);
            pointCaret = new Point(i_point);            if (i_char_loc == 0)
            {
                pointCaret = new Point(0);
            }
            else if (i_char_loc >= this.Text.Length)
            {
                pi_char_loc = new IntPtr(i_char_loc - 1);
                i_point = win32.SendMessage(this.Handle, win32.EM_POSFROMCHAR, pi_char_loc, IntPtr.Zero);
                pointCaret = new Point(i_point);                Graphics g = this.CreateGraphics();
                String t1 = this.Text.Substring(this.Text.Length - 1, 1) + "X";
                SizeF sizet1 = g.MeasureString(t1, this.Font);
                SizeF sizex = g.MeasureString("X", this.Font);
                g.Dispose();
                int xoffset = (int)(sizet1.Width - sizex.Width);
                pointCaret.X = pointCaret.X + xoffset;                if (i_char_loc == this.Text.Length)
                {
                    String slast = this.Text.Substring(Text.Length - 1, 1);
                    if (slast == "\n")
                    {
                        pointCaret.X = 1;
                        pointCaret.Y = pointCaret.Y + myFontHeight;
                    }
                }            }
            return pointCaret;
        }
        private void myTimer1_Tick(object sender, EventArgs e)
        {
            //Timer used to turn caret on and off for focused control            myCaretState = !myCaretState;
            myCaretUpToDate = false;
            this.Invalidate();
        }
        private class uPictureBox : PictureBox
        {
            public uPictureBox()
            {
                this.SetStyle(ControlStyles.Selectable, false);
                this.SetStyle(ControlStyles.UserPaint, true);
                this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
                this.SetStyle(ControlStyles.DoubleBuffer, true);                this.Cursor = null;
                this.Enabled = true;
                this.SizeMode = PictureBoxSizeMode.Normal;
            }            protected override void WndProc(ref Message m)
            {
                if (m.Msg == win32.WM_LBUTTONDOWN
                 || m.Msg == win32.WM_RBUTTONDOWN
                 || m.Msg == win32.WM_LBUTTONDBLCLK
                 || m.Msg == win32.WM_MOUSELEAVE
                 || m.Msg == win32.WM_MOUSEMOVE)
                {
                    win32.PostMessage(this.Parent.Handle, (uint)m.Msg, m.WParam, m.LParam);
                }                else if (m.Msg == win32.WM_LBUTTONUP)
                {
                    this.Parent.Invalidate();
                }
                base.WndProc(ref m);
            }
        }   // End uPictureBox Class
        #endregion  // end private functions and classes
        #region Component Designer generated code
        private void InitializeComponent()
        {
            components = new System.ComponentModel.Container();
        }
        #endregion
        #region New Public Properties
        [
        Category("Appearance"),
        Description("The alpha value used to blend the control's background. Valid values are 0 through 255."),
        Browsable(true),
        DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)
        ]
        public int BackAlpha
        {
            get { return myBackAlpha; }
            set
            {
                int v = value;
                if (v > 255)
                    v = 255;
                myBackAlpha = v;
                myUpToDate = false;
                Invalidate();
            }
        }
        #endregion
    }
}  

用richtextbox不就行了吗using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;namespace CusLib
{
    public partial class TransparentRichTextBox : RichTextBox
    {
        public TransparentRichTextBox()
        {
            base.ScrollBars = RichTextBoxScrollBars.None;
            SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.ResizeRedraw | ControlStyles.SupportsTransparentBackColor | ControlStyles.UserPaint, true);
            SetStyle(ControlStyles.Opaque, false);
            UpdateStyles();
        }        override protected CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x20;
                return cp;
            }
        }        override protected void OnPaintBackground(PaintEventArgs e)
        {
        }
    }
}