DragDrop+Transparent Panel == BLINKing

Question

here is full code: using System; using System.Drawing; using System.Collections; using System.ComponentModel; using System.Windows.Forms; namespace wg2h { /// /// Summary description for WYSIWYG. /// public class WG : System.Windows.Forms.Form { private Panel DraggingPanel; private int offX; private int offY; private Point loc=new Point(1000,1000); public static Form wf=new WG(); private wg2h.DivPanel p0; private System.Windows.Forms.Label label1; /// /// Required designer variable. /// private System.ComponentModel.Container components = null; public WG() { ResizeRedraw = true; SetStyle(ControlStyles.DoubleBuffer | ControlStyles.UserPaint | ControlStyles.AllPaintingInWmPaint, true); // // Required for Windows Form Designer support // InitializeComponent(); // // TODO: Add any constructor code after InitializeComponent call // } /// /// Clean up any resources being used. /// protected override void Dispose( bool disposing ) { if( disposing ) { if(components != null) { components.Dispose(); } } base.Dispose( disposing ); } #region Windows Form Designer generated code /// /// Required method for Designer support - do not modify /// the contents of this method with the code editor. /// private void InitializeComponent() { this.p0 = new wg2h.DivPanel(); this.label1 = new System.Windows.Forms.Label(); this.SuspendLayout(); // // p0 // this.p0.AllowDrop = true; this.p0.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle; this.p0.Dock = System.Windows.Forms.DockStyle.Fill; this.p0.Location = new System.Drawing.Point(0, 0); this.p0.Name = "p0"; this.p0.Size = new System.Drawing.Size(610, 475); this.p0.TabIndex = 0; this.p0.DragEnter += new System.Windows.Forms.DragEventHandler(this.OnPanelDragEnter); this.p0.DragOver += new System.Windows.Forms.DragEventHandler(this.OnPanelDragOver); // // label1 // this.label1.Location = new System.Drawing.Point(0, 0); this.label1.Name = "label1"; this.label1.TabIndex = 0; // // WG // this.AutoScaleBaseSize = new System.Drawing.Size(5, 13); this.BackColor = System.Drawing.SystemColors.ControlLightLight; this.ClientSize = new System.Drawing.Size(610, 475); this.Controls.Add(this.p0); this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedToolWindow; this.Name = "WG"; this.Text = "WYSIWYG"; this.Load += new System.EventHandler(this.WG_Load); this.ResumeLayout(false); } #endregion [STAThread] public static void Main(){Application.Run(wf);} private void OnPanelMouseDown(object sender, System.Windows.Forms.MouseEventArgs e) { this.offX=e.X; this.offY=e.Y; Panel tsender=(Panel)sender; this.DraggingPanel=tsender; this.DoDragDrop(tsender,DragDropEffects.Move); } private void OnPanelMouseLeave(object sender, System.EventArgs e) { } private void OnPanelDragEnter(object sender, System.Windows.Forms.DragEventArgs e) { e.Effect=DragDropEffects.Move; } private void OnPanelDragOver(object sender, System.Windows.Forms.DragEventArgs e) { DivPanel d_panel = sender as DivPanel; Point cu=Cursor.Position; cu=DraggingPanel.Parent.PointToClient(cu); cu.Offset(-this.offX,-this.offY); d_panel.Parent.Invalidate(new Rectangle(d_panel.Parent.PointToClient(DraggingPanel.Parent.PointToScreen(DraggingPanel.Location)),DraggingPanel.Size),true); this.DraggingPanel.Location=new Point(cu.X,cu.Y); } private void WG_Load(object sender, System.EventArgs e) { Control px=new DivPanel(); px.Location=new Point(0,0); px.Size=new Size(100, 200); px.AllowDrop=false; this.p0.Controls.Add(px); px.BringToFront(); px.DragEnter += new System.Windows.Forms.DragEventHandler(this.OnPanelDragEnter); px.MouseHover += new System.EventHandler(this.OnPanelMouseLeave); px.DragOver += new System.Windows.Forms.DragEventHandler(this.OnPanelDragOver); px.MouseLeave += new System.EventHandler(this.OnPanelMouseLeave); px.MouseDown += new System.Windows.Forms.MouseEventHandler(this.OnPanelMouseDown); px=new DivPanel(); px.Location=new Point(0,0); px.Size=new Size(100, 200); px.AllowDrop=false; this.p0.Controls.Add(px); px.BringToFront(); px.DragEnter += new System.Windows.Forms.DragEventHandler(this.OnPanelDragEnter); px.MouseHover += new System.EventHandler(this.OnPanelMouseLeave); px.DragOver += new System.Windows.Forms.DragEventHandler(this.OnPanelDragOver); px.MouseLeave += new System.EventHandler(this.OnPanelMouseLeave); px.MouseDown += new System.Windows.Forms.MouseEventHandler(this.OnPanelMouseDown); } } public class DivPanel:System.Windows.Forms.Panel { public DivPanel() { //??? ???????????? ????????? ????? SetStyle(ControlStyles.Opaque, true); SetStyle(ControlStyles.DoubleBuffer,true); SetStyle(ControlStyles.UserPaint,true); this.BorderStyle=BorderStyle.FixedSingle; } //??????? ? ????, ??? ??? ????????, WS_EX_TRANSPARENT ??? ????????????: protected override CreateParams CreateParams { get { const int WS_EX_TRANSPARENT = 0x00000020; CreateParams createParams = base.CreateParams; createParams.ExStyle |= WS_EX_TRANSPARENT; return createParams; } } protected override void OnPaint(System.Windows.Forms.PaintEventArgs e) { // TODO: Add DivPanel.OnPaint implementation //?????? ?????? base.OnPaint (e); this.BorderStyle=BorderStyle.FixedSingle; if(this.Parent is DivPanel)e.Graphics.FillRectangle(new SolidBrush(Color.FromArgb(100, Color.Red)),0, 0, Width, Height); } //???????? ??????? ?????: protected override void OnBackColorChanged(EventArgs e) { // TODO: Add DivPanel.OnBackColorChanged implementation //base.OnBackColorChanged (e); } } } DivPanels blinking ,as you see... and nobody can tell me what's the ...