TCustomControl绘制自己和图形子控件共四步，TWinControl关键属性方法速记

  TCustomControl = class(TWinControl)

  private

    FCanvas: TCanvas;

    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;

  protected

    procedure Paint; virtual;

    procedure PaintWindow(DC: HDC); override;

    property Canvas: TCanvas read FCanvas; // 到这步才有Canvas

  public

    constructor Create(AOwner: TComponent); override;

    destructor Destroy; override;

  end;

constructor TCustomControl.Create(AOwner: TComponent);

begin

  inherited Create(AOwner);

  FCanvas := TControlCanvas.Create;

  TControlCanvas(FCanvas).Control := Self;

end;

destructor TCustomControl.Destroy;

begin

  FCanvas.Free;

  inherited Destroy;

end;

procedure TCustomControl.WMPaint(var Message: TWMPaint); // 第一步，接受到自绘消息

begin

  Include(FControlState, csCustomPaint); // 进入自绘状态

  inherited; // 第二步，调用VCL框架提供的同名管理函数（TWinControl.WMPaint）来重绘所有子控件和自己。有个问题：如果每个TCustomControl都要求父控件重绘一遍，会不会效率很低？

  Exclude(FControlState, csCustomPaint); // 结束自绘状态

end;

procedure TCustomControl.PaintWindow(DC: HDC); // 第三步，等待VCL框架的管理函数（TWinControl.WMPaint-->TWinControl.PaintHandler-->当前函数）来调用自己（只能是控件重绘自己时产生的调用，至于当前控件的WinControl子控件的重绘属由更高层次TWinControl.UpdateShowing来管理，而不归这些低层次的函数来管理）

begin

  FCanvas.Lock;

  try

    FCanvas.Handle := DC;

    try

      TControlCanvas(FCanvas).UpdateTextFlags;

      Paint; // 第四步，进一步调用自己的Paint虚函数

    finally

      FCanvas.Handle := 0; // 当场释放资源

    end;

  finally

    FCanvas.Unlock;

  end;

end;

procedure TCustomControl.Paint; // 提前准备：程序员覆盖这个方法，真正调用程序员的绘制函数（默认为空，等待程序员来绘制）

begin

end;

新发现一个函数（尽管不起作用）：

procedure TWinControl.PaintWindow(DC: HDC);

var

  Message: TMessage;

begin

  Message.Msg := WM_PAINT;

  Message.WParam := DC;

  Message.LParam := ;

  Message.Result := ;

  DefaultHandler(Message);

end;

TWinControl用来处理鼠标和实际重绘，而处理鼠标全部在TControl里。此外还申请句柄，处理自己绘图，与父类的交互。虽然TControl也有绘图，但最后还是要让父类TWinControl来画。

  TWinControl = class(TControl)

    constructor Create(AOwner: TComponent); override;

    constructor CreateParented(ParentWindow: HWnd);

    class function CreateParentedControl(ParentWindow: HWND): TWinControl;

    destructor Destroy; override;

    procedure Broadcast(var Message);

    function GetHandle: HWND;

    procedure SetParentWindow(Value: HWND);

    function GetControlCount: Integer;

    function GetControl(Index: Integer): TControl;

    procedure Insert(AControl: TControl);

    procedure SetZOrderPosition(Position: Integer);

    function HandleAllocated: Boolean;

    procedure HandleNeeded;

    procedure InsertControl(AControl: TControl);

    procedure CreateHandle; virtual;

    procedure CreateParams(var Params: TCreateParams); virtual;

    procedure CreateWindowHandle(const Params: TCreateParams); virtual;

    procedure CreateWnd; virtual;

    procedure RecreateWnd;

    procedure DestroyHandle; virtual;

    procedure DestroyWindowHandle; virtual;

    procedure DestroyWnd; virtual;

    function GetDeviceContext(var WindowHandle: HWND): HDC; overload; override;

    function GetParentHandle: HWND;

    function GetTopParentHandle: HWnd;

    procedure SetParent(AParent: TWinControl); override;

    procedure SetParentBackground(Value: Boolean); virtual;

    procedure SetParentDoubleBuffered(Value: Boolean); virtual;

    procedure SetZOrder(TopMost: Boolean); override;

    procedure RemoveControl(AControl: TControl);procedure UpdateControlState;
    procedure CreateSubClass(var Params: TCreateParams; ControlClassName: PChar); // 超类化

    procedure WndProc(var Message: TMessage); override;

    property DefWndProc: Pointer read FDefWndProc write FDefWndProc;

    property WindowHandle: HWnd read FHandle write FHandle;

    procedure DefaultHandler(var Message); override;

    procedure MainWndProc(var Message: TMessage);

    function PreProcessMessage(var Msg: TMsg): Boolean; dynamic;

    procedure Repaint; override; // 就两句：调用 类函数Invalidate; 和 类函数Update（今天怎么觉得思路格外清楚啊）; // 让程序员有机会总揽全局，既使控件失效，又立即重绘，因为一般情况下只需要让控件失效即可，然后系统空闲时发信息让控件重绘，程序员不需要管理和调用后者。
    procedure Notification(AComponent: TComponent; Operation: TOperation); override;

    procedure NotifyControls(Msg: Word);

    procedure PaintControls(DC: HDC; First: TControl); // 给FControls发Perform(WM_PAINT, DC, 0); 把图像子控件全部重绘了一遍。对所有的FWinControls 调用WinAPI FrameRect 用指定的画刷为指定的矩形画边框

 UpdateShowing; // 只处理是否Visible

    procedure Invalidate; override; // 内容就一句 Perform(CM_INVALIDATE, 0, 0); 另外观察一下TControl.Invalidate;函数 也是就一句：InvalidateControl(Visible, csOpaque in ControlStyle); 
    procedure PaintTo(Canvas: TCanvas; X, Y: Integer); overload;

    procedure Update; override; // 调用WinAPI函数 if HandleAllocated then UpdateWindow(WindowHandle); // 会产生WM_PAINT消息。让程序员有机会强行自绘控件。

    总结：自绘过程一共有四个函数实际干活，第一步是收到系统消息调用WMPaint，第二步把消息转交给PaintHandler，第三步首先绘制自己，即调用自己的PaintWindow，第四步调用PaintControls绘制所有子控件（会给所有子控件挨个发送WM_PAINT）。
    备注：对于一个单独的控件自己而言，重绘其实就两步，第一步让控件失效，第二步等待系统给Win控件发送WM_PAINT后真正重绘，但是也可由程序员强迫立即重绘（UpdateWindow）。具体重绘过程由VCL控制，包含了自动重绘图形子控件和调用程序员的事件

    procedure AssignTo(Dest: TPersistent); override;

    function GetClientRect: TRect; override;

    function IsDoubleBufferedStored: Boolean;

    procedure SetDoubleBuffered(Value: Boolean);

    procedure DoEnter; dynamic;

    procedure DoExit; dynamic;

    function DoKeyDown(var Message: TWMKey): Boolean;

    function DoKeyPress(var Message: TWMKey): Boolean;

    function DoKeyUp(var Message: TWMKey): Boolean;

    procedure WMInputLangChange(var Message: TMessage); message WM_INPUTLANGCHANGE; // 输入法改变

    procedure WMPaint(var Message: TWMPaint); message WM_PAINT; // 这里只是收到消息，收到以后怎么做不一定要放在这里。实际上：如果不双缓冲就调用 PaintHandler，否则立刻重绘（并且还考虑Windows主题的影响）。

    procedure WMCommand(var Message: TWMCommand); message WM_COMMAND; // 菜单、工具栏命令

    procedure WMNotify(var Message: TWMNotify); message WM_NOTIFY; // 通知消息

    procedure WMSysColorChange(var Message: TWMSysColorChange); message WM_SYSCOLORCHANGE; // 系统颜色改变

    procedure WMHScroll(var Message: TWMHScroll); message WM_HSCROLL;

    procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;

    procedure WMCompareItem(var Message: TWMCompareItem); message WM_COMPAREITEM;

    procedure WMDeleteItem(var Message: TWMDeleteItem); message WM_DELETEITEM;

    procedure WMDrawItem(var Message: TWMDrawItem); message WM_DRAWITEM;

    procedure WMMeasureItem(var Message: TWMMeasureItem); message WM_MEASUREITEM;

    procedure WMEraseBkgnd(var Message: TWmEraseBkgnd); message WM_ERASEBKGND; // 画背景色，间接的发送 WM_ERASEBKGND消息，不实际干活

    procedure WMWindowPosChanged(var Message: TWMWindowPosChanged); message WM_WINDOWPOSCHANGED; // 位置改变

    procedure WMWindowPosChanging(var Message: TWMWindowPosChanging); message WM_WINDOWPOSCHANGING;

    procedure WMSize(var Message: TWMSize); message WM_SIZE;

    procedure WMMove(var Message: TWMMove); message WM_MOVE;

    procedure WMSetCursor(var Message: TWMSetCursor); message WM_SETCURSOR; // 设置光标

    procedure WMKeyDown(var Message: TWMKeyDown); message WM_KEYDOWN; // 按键方法

    procedure WMSysKeyDown(var Message: TWMSysKeyDown); message WM_SYSKEYDOWN;

    procedure WMKeyUp(var Message: TWMKeyUp); message WM_KEYUP;

    procedure WMSysKeyUp(var Message: TWMSysKeyUp); message WM_SYSKEYUP; // 系统按键

    procedure WMChar(var Message: TWMChar); message WM_CHAR;

    procedure WMSysCommand(var Message: TWMSysCommand); message WM_SYSCOMMAND; // 系统命令

    procedure WMCharToItem(var Message: TWMCharToItem); message WM_CHARTOITEM;

    procedure WMParentNotify(var Message: TWMParentNotify); message WM_PARENTNOTIFY; // 父控件通知

    procedure WMVKeyToItem(var Message: TWMVKeyToItem); message WM_VKEYTOITEM;

    procedure WMDestroy(var Message: TWMDestroy); message WM_DESTROY; // 销毁

    procedure WMMouseActivate(var Message: TWMMouseActivate); message WM_MOUSEACTIVATE;

    procedure WMNCCalcSize(var Message: TWMNCCalcSize); message WM_NCCALCSIZE; // 非客户区重新计算

    procedure WMNCDestroy(var Message: TWMNCDestroy); message WM_NCDESTROY; // 非客户区销毁

    procedure WMNCHitTest(var Message: TWMNCHitTest); message WM_NCHITTEST;

    procedure WMNCPaint(var Message: TWMNCPaint); message WM_NCPAINT; // 非客户区绘图

    procedure WMQueryNewPalette(var Message: TMessage); message WM_QUERYNEWPALETTE;

    procedure WMPaletteChanged(var Message: TMessage); message WM_PALETTECHANGED;

    procedure WMWinIniChange(var Message: TMessage); message WM_WININICHANGE;

    procedure WMFontChange(var Message: TMessage); message WM_FONTCHANGE; // 字体被改变

    procedure WMTimeChange(var Message: TMessage); message WM_TIMECHANGE; // 时间被改变

    procedure WMSetFocus(var Message: TWMSetFocus); message WM_SETFOCUS;

    procedure WMKillFocus(var Message: TWMKillFocus); message WM_KILLFOCUS;

    procedure WMIMEStartComp(var Message: TMessage); message WM_IME_STARTCOMPOSITION;

    procedure WMIMEEndComp(var Message: TMessage); message WM_IME_ENDCOMPOSITION;

    procedure WMContextMenu(var Message: TWMContextMenu); message WM_CONTEXTMENU;

    procedure WMGesture(var Message: TMessage); message WM_GESTURE;

    procedure WMGestureNotify(var Message: TWMGestureNotify); message WM_GESTURENOTIFY;

    procedure WMTabletQuerySystemGestureStatus(var Message: TMessage); message WM_TABLET_QUERYSYSTEMGESTURESTATUS;

    procedure WMPrintClient(var Message: TWMPrintClient); message WM_PRINTCLIENT;

    procedure CMInputLangChange(var Message: TMessage); message CM_INPUTLANGCHANGE;

    procedure CMChanged(var Message: TCMChanged); message CM_CHANGED;

    procedure CMChildKey(var Message: TCMChildKey); message CM_CHILDKEY;

    procedure CMDialogKey(var Message: TCMDialogKey); message CM_DIALOGKEY;

    procedure CMDialogChar(var Message: TCMDialogChar); message CM_DIALOGCHAR;

    procedure CMVisibleChanged(var Message: TMessage); message CM_VISIBLECHANGED;

    procedure CMEnabledChanged(var Message: TMessage); message CM_ENABLEDCHANGED;

    procedure CMColorChanged(var Message: TMessage); message CM_COLORCHANGED;

    procedure CMFontChanged(var Message: TMessage); message CM_FONTCHANGED;

    procedure CMBorderChanged(var Message: TMessage); message CM_BORDERCHANGED;

    procedure CMCursorChanged(var Message: TMessage); message CM_CURSORCHANGED;

    procedure CMCtl3DChanged(var Message: TMessage); message CM_CTL3DCHANGED;

    procedure CMParentCtl3DChanged(var Message: TMessage); message CM_PARENTCTL3DCHANGED;

    procedure CMParentDoubleBufferedChanged(var Message: TMessage); message CM_PARENTDOUBLEBUFFEREDCHANGED;

    procedure CMShowingChanged(var Message: TMessage); message CM_SHOWINGCHANGED;

    procedure CMShowHintChanged(var Message: TMessage); message CM_SHOWHINTCHANGED;

    procedure CMEnter(var Message: TCMEnter); message CM_ENTER;

    procedure CMExit(var Message: TCMExit); message CM_EXIT;

    procedure CMDesignHitTest(var Message: TCMDesignHitTest); message CM_DESIGNHITTEST;

    procedure CMSysColorChange(var Message: TMessage); message CM_SYSCOLORCHANGE;

    procedure CMSysFontChanged(var Message: TMessage); message CM_SYSFONTCHANGED;

    procedure CMWinIniChange(var Message: TWMWinIniChange); message CM_WININICHANGE;

    procedure CMFontChange(var Message: TMessage); message CM_FONTCHANGE;

    procedure CMTimeChange(var Message: TMessage); message CM_TIMECHANGE;

    procedure CMDrag(var Message: TCMDrag); message CM_DRAG;

    procedure CNKeyDown(var Message: TWMKeyDown); message CN_KEYDOWN;

    procedure CNKeyUp(var Message: TWMKeyUp); message CN_KEYUP;

    procedure CNChar(var Message: TWMChar); message CN_CHAR;

    procedure CNSysKeyDown(var Message: TWMKeyDown); message CN_SYSKEYDOWN;

    procedure CNSysChar(var Message: TWMChar); message CN_SYSCHAR;

    procedure CMRecreateWnd(var Message: TMessage); message CM_RECREATEWND;

    procedure CMInvalidate(var Message: TMessage); message CM_INVALIDATE;

    procedure CMBiDiModeChanged(var Message: TMessage); message CM_BIDIMODECHANGED;

    procedure CMDoubleBufferedChanged(var Message: TMessage); message CM_DOUBLEBUFFEREDCHANGED;

    procedure CMTextChanged(var Message: TMessage); message CM_TEXTCHANGED;

    procedure CMTabletOptionsChanged(var Message: TMessage); message CM_TABLETOPTIONSCHANGED;

    procedure CMFocusChanged(var Message: TCMFocusChanged); message CM_FOCUSCHANGED;

    procedure CMControlListChange(var Message: TMessage); message CM_CONTROLLISTCHANGE;

    procedure CMControlListChanging(var Message: TMessage); message CM_CONTROLLISTCHANGING;

    procedure CMDockClient(var Message: TCMDockClient); message CM_DOCKCLIENT;

    procedure CMUnDockClient(var Message: TCMUnDockClient); message CM_UNDOCKCLIENT;

    procedure CMFloat(var Message: TCMFloat); message CM_FLOAT;

    property Brush: TBrush read FBrush;

    property Controls[Index: Integer]: TControl read GetControl;

    property ControlCount: Integer read GetControlCount;

    property Handle: HWND read GetHandle;

    property ParentDoubleBuffered: Boolean read FParentDoubleBuffered write SetParentDoubleBuffered default True;

    property ParentWindow: HWND read FParentWindow write SetParentWindow;

    property Showing: Boolean read FShowing;

贴一下TWinControl的几个关键的自绘代码：

procedure TWinControl.Repaint;

begin

  Invalidate;

  Update;

end;

procedure TWinControl.Invalidate;

begin

  Perform(CM_INVALIDATE, , );

end;

procedure TWinControl.CMInvalidate(var Message: TMessage);

var

  I: Integer;

begin

  if HandleAllocated then

  begin

    if Parent <> nil then Parent.Perform(CM_INVALIDATE, , );

    if Message.WParam =  then

    begin

      InvalidateRect(FHandle, nil, not (csOpaque in ControlStyle));

      { Invalidate child windows which use the parentbackground when themed }

      if ThemeServices.ThemesEnabled then

        for I :=  to ControlCount -  do

          if csParentBackground in Controls[I].ControlStyle then

            Controls[I].Invalidate;

    end;

  end;

end;

procedure TWinControl.Update;

begin

  if HandleAllocated then UpdateWindow(FHandle);

end;

TWinControl的属性：

    FDefWndProc: Pointer;

    FHandle: HWnd;

    FObjectInstance: Pointer;

    FParentWindow: HWND;

    FBrush: TBrush;

    FControls: TList;

    FWinControls: TList;

    FAlignControlList: TList;

    FParentDoubleBuffered: Boolean;

    FDoubleBuffered: Boolean;

    FDesignSize: TPoint;

    FMouseControl: TControl;

    FTouchControl: TControl;

    FOnEnter: TNotifyEvent;

    FOnExit: TNotifyEvent;

    FOnKeyDown: TKeyEvent;

    FOnKeyUp: TKeyEvent;

    FOnKeyPress: TKeyPressEvent;

再来窗口参数：

  TCreateParams = record

    Caption: PChar;

    Style: DWORD;

    ExStyle: DWORD;

    X, Y: Integer;

    Width, Height: Integer;

    WndParent: HWnd;

    Param: Pointer;

    WindowClass: TWndClass;

    WinClassName: array[..] of Char;

  end;

PaintControls的定义，一共2处调用：

procedure TControl.Repaint;

var

  DC: HDC;

begin

  if (Visible or (csDesigning in ComponentState) and

    not (csNoDesignVisible in ControlStyle)) and (Parent <> nil) and

    Parent.HandleAllocated then

    if csOpaque in ControlStyle then

    begin

      DC := GetDC(Parent.Handle);

      try

        IntersectClipRect(DC, Left, Top, Left + Width, Top + Height);

        Parent.PaintControls(DC, Self); // 写清楚了，要求父控件更新当前图形控件的显示（而不是重绘全部子控件）

      finally

        ReleaseDC(Parent.Handle, DC);

      end;

    end else

    begin

      Invalidate;

      Update;

    end;

end;

procedure TWinControl.PaintHandler(var Message: TWMPaint);

var

  I, Clip, SaveIndex: Integer;

  DC: HDC;

  PS: TPaintStruct;

begin

  DC := Message.DC;

  if DC =  then DC := BeginPaint(Handle, PS);

  try

    if FControls = nil then PaintWindow(DC) else // 不含子控件的话，直接重绘控件自己

    begin

      SaveIndex := SaveDC(DC);

      Clip := SimpleRegion;

      for I :=  to FControls.Count -  do

        with TControl(FControls[I]) do

          if (Visible or (csDesigning in ComponentState) and

            not (csNoDesignVisible in ControlStyle)) and

            (csOpaque in ControlStyle) then

          begin

            Clip := ExcludeClipRect(DC, Left, Top, Left + Width, Top + Height);

            if Clip = NullRegion then Break;

          end;

      if Clip <> NullRegion then PaintWindow(DC); // 如果根据所有图形子控件的区域计算以后，发现真的有无效区域，才进行重绘

      RestoreDC(DC, SaveIndex);

    end;

    PaintControls(DC, nil); // 当重绘全部图形子控件的时候，第二个参数就传入nil

  finally

    if Message.DC =  then EndPaint(Handle, PS);

  end;

end;

procedure TWinControl.PaintControls(DC: HDC; First: TControl);

var

  I, Count, SaveIndex: Integer;

  FrameBrush: HBRUSH;

begin

  if DockSite and UseDockManager and (DockManager <> nil) then

    DockManager.PaintSite(DC);

  if FControls <> nil then // 就像这个函数名字的含义一样，真的是只重绘所有图形子控件，而不重绘它的WinControl子控件（只重绘它们的边框）

  begin

    I := ;

    if First <> nil then

    begin

      I := FControls.IndexOf(First);

      if I <  then I := ;

    end;

    Count := FControls.Count;

    while I < Count do

    begin

      with TControl(FControls[I]) do

        if (Visible or (csDesigning in ComponentState) and

          not (csNoDesignVisible in ControlStyle)) and

          RectVisible(DC, Rect(Left, Top, Left + Width, Top + Height)) then

        begin

          if csPaintCopy in Self.ControlState then

            Include(FControlState, csPaintCopy);

          SaveIndex := SaveDC(DC);

          MoveWindowOrg(DC, Left, Top);

          IntersectClipRect(DC, , , Width, Height);

          Perform(WM_PAINT, DC, 0);

          RestoreDC(DC, SaveIndex);

          Exclude(FControlState, csPaintCopy);

        end;

      Inc(I);

    end;

  end;

  if FWinControls <> nil then

    for I :=  to FWinControls.Count -  do

      with TWinControl(FWinControls[I]) do

        if FCtl3D and (csFramed in ControlStyle) and

          (Visible or (csDesigning in ComponentState) and

          not (csNoDesignVisible in ControlStyle)) then

        begin // 只重绘WinControl子控件的边框，而不是重绘整个控件

          FrameBrush := CreateSolidBrush(ColorToRGB(clBtnShadow));

          FrameRect(DC, Rect(Left - , Top - , Left + Width, Top + Height),

            FrameBrush);

          DeleteObject(FrameBrush);

          FrameBrush := CreateSolidBrush(ColorToRGB(clBtnHighlight));

          FrameRect(DC, Rect(Left, Top, Left + Width + , Top + Height + ),

            FrameBrush);

          DeleteObject(FrameBrush);

        end;

end;

另外，整个Controls.pas里一共有7处取DC（搜索DC :=），其实重要的地方只有三处（TWinControl.PaintHandler和TControl.Repaint和TWinControl.WMPaint），总体方针是DC现用现取：

procedure TWinControl.PaintHandler(var Message: TWMPaint);

var

  I, Clip, SaveIndex: Integer;

  DC: HDC;

  PS: TPaintStruct;

begin

  DC := Message.DC;

  if DC =  then DC := BeginPaint(Handle, PS);

  try

    if FControls = nil then PaintWindow(DC) else

procedure TControl.Repaint;

var

  DC: HDC;

begin

  if (Visible or (csDesigning in ComponentState) and

    not (csNoDesignVisible in ControlStyle)) and (Parent <> nil) and

    Parent.HandleAllocated then

    if csOpaque in ControlStyle then

    begin

      DC := GetDC(Parent.Handle);

function TControl.PaletteChanged(Foreground: Boolean): Boolean;

var

  OldPalette, Palette: HPALETTE;

  WindowHandle: HWnd;

  DC: HDC;

begin

  Result := False;

  if not Visible then Exit;

  Palette := GetPalette;

  if Palette <>  then

  begin

    DC := GetDeviceContext(WindowHandle);

procedure TControl.DefaultDockImage(DragDockObject: TDragDockObject;

  Erase: Boolean);

var

  DesktopWindow: HWND;

  DC: HDC;

  OldBrush: HBrush;

  DrawRect: TRect;

  PenSize: Integer;

begin

  with DragDockObject do

  begin

    PenSize := FrameWidth;

    if Erase then DrawRect := FEraseDockRect

    else DrawRect := FDockRect;

  end;

  DesktopWindow := GetDesktopWindow;

  DC := GetDCEx(DesktopWindow, 0, DCX_CACHE or DCX_LOCKWINDOWUPDATE);

procedure TWinControl.WMNCPaint(var Message: TMessage);

var

  DC: HDC;

  RC, RW, SaveRW: TRect;

  EdgeSize: Integer;

  WinStyle: Longint;

begin

  { Get window DC that is clipped to the non-client area }

  if (BevelKind <> bkNone) or (BorderWidth > ) then

  begin

    DC := GetWindowDC(Handle);

    try

      Windows.GetClientRect(Handle, RC);

procedure THintWindow.WMNCPaint(var Message: TMessage);

var

  DC: HDC;

begin

  DC := GetWindowDC(Handle);

  try

    NCPaint(DC);

  finally

    ReleaseDC(Handle, DC);

  end;

end;

procedure TWinControl.WMPaint(var Message: TWMPaint);

var

  DC, MemDC: HDC;

  MemBitmap, OldBitmap: HBITMAP;

  PS: TPaintStruct;

begin

  if not FDoubleBuffered or (Message.DC <> ) then

  begin

    if not (csCustomPaint in ControlState) and (ControlCount = ) then

      inherited

    else

      PaintHandler(Message);

  end

  else

  begin

    DC := GetDC(0); // 取桌面的DC

    MemBitmap := CreateCompatibleBitmap(DC, ClientRect.Right, ClientRect.Bottom);

    ReleaseDC(, DC);

    MemDC := CreateCompatibleDC();

    OldBitmap := SelectObject(MemDC, MemBitmap);

    try

      DC := BeginPaint(Handle, PS);

      Perform(WM_ERASEBKGND, MemDC, MemDC);

      Message.DC := MemDC;

      WMPaint(Message);

      Message.DC := ;

      BitBlt(DC, , , ClientRect.Right, ClientRect.Bottom, MemDC, , , SRCCOPY);

      EndPaint(Handle, PS);

    finally

      SelectObject(MemDC, OldBitmap);

      DeleteDC(MemDC);

      DeleteObject(MemBitmap);

    end;

  end;

end;

再研究Canvas，待续。。。

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