再开新贴讨论，mdejtod 或其他熟悉Gdi+的进，解决后一起结贴给分！

Question

前两贴地址：
http://topic.csdn.net/u/20111118/07/da4a9390-82df-4c23-88fc-90193b9e330b.html
(已结)
http://topic.csdn.net/u/20111129/21/2f3a8d3c-def9-4427-a505-7ccd6fbde2de.html
(未结)一段时间没搞它了
再翻出来，我找到问题了，再次求教！当按件被其他窗体或滚动到不可见区域，再次出现时，Windows自动发出WM_Paint消息！
这时候就有问题了！
若仅是有部分被挡住，重绘的时候，未被挡住的部分，也会再绘制一次，这样就造成同一个控件两部分不一样
（因为和透明渐变，所以效果不一样了！）
求教：
怎么样让它在重绘之前，清除其内容呢？或者说恢复控件未被重绘时的状态呢？期待 mdejtod 再次出现……

Answer 1

unit SkinScrollBox;interfaceuses
  Windows,SysUtils,Classes,Controls,Forms,GdiPlus,Messages;
type
  TSkinScrollBox=class(TScrollBox)
  protected
    procedure WMEraseBkGnd(var Message:TWMEraseBkGnd);message WM_ERASEBKGND;
    procedure WMHScroll(var Message: TWMHScroll); message WM_HSCROLL;
    procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
    procedure PaintWindow(DC: HDC); override;
    procedure WMSize(var Message: TWMSize); message WM_SIZE;
  public
    constructor Create(AOwner:TComponent);override;
    destructor Destroy;override;
  published
    property Align;
    property Anchors;
    property AutoScroll;
    property AutoSize;
    property BevelEdges;
    property BevelInner;
    property BevelOuter;
    property BevelKind;
    property BevelWidth;
    property BiDiMode;
    property BorderStyle;
    property Constraints;
    property DockSite;
    property DoubleBuffered;
    property DragCursor;
    property DragKind;
    property DragMode;
    property Enabled;
    property Color;
    property Ctl3D;
    property Font;
    property Padding;
    property ParentBiDiMode;
    property ParentBackground default False;
    property ParentColor;
    property ParentCtl3D;
    property ParentDoubleBuffered;
    property ParentFont;
    property ParentShowHint;
    property PopupMenu;
    property ShowHint;
    property TabOrder;
    property TabStop;
    property Touch;
    property Visible;
    property OnCanResize;
    property OnClick;
    property OnConstrainedResize;
    property OnContextPopup;
    property OnDblClick;
    property OnDockDrop;
    property OnDockOver;
    property OnDragDrop;
    property OnDragOver;
    property OnEndDock;
    property OnEndDrag;
    property OnEnter;
    property OnExit;
    property OnGesture;
    property OnGetSiteInfo;
    property OnMouseActivate;
    property OnMouseDown;
    property OnMouseEnter;
    property OnMouseLeave;
    property OnMouseMove;
    property OnMouseUp;
    property OnMouseWheel;
    property OnMouseWheelDown;
    property OnMouseWheelUp;
    property OnResize;
    property OnStartDock;
    property OnStartDrag;
    property OnUnDock;
  end;procedure Register;implementationprocedure Register;
begin
  RegisterComponents('SkinEngine',[TSkinScrollBox]);
end;{ TSkinScrollBox }constructor TSkinScrollBox.Create(AOwner: TComponent);
begin
  inherited;end;destructor TSkinScrollBox.Destroy;
begin  inherited;
end;procedure TSkinScrollBox.PaintWindow(DC: HDC);
var
  Brush:IGpLinearGradientBrush;
  Graphics:IGPGraphics;
begin
  Graphics:=TGPGraphics.Create(DC);
  Brush:=TGpLinearGradientBrush.Create(TGPRect.Create(ClientRect),
            TGPColor.Blue,
            TGPColor.Gray,
            TGPLinearGradientMode.LinearGradientModeVertical);
  Graphics.FillRectangle(Brush,TGPRect.Create(ClientRect));
end;procedure TSkinScrollBox.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  Message.Result:=1;
end;procedure TSkinScrollBox.WMHScroll(var Message: TWMHScroll);
begin
  Inherited;
  Invalidate;
end;procedure TSkinScrollBox.WMPaint(var Message: TWMPaint);
begin
  ControlState:=ControlState+[csCustomPaint];
  inherited;
  ControlState:=ControlState-[csCustomPaint];
end;procedure TSkinScrollBox.WMSize(var Message: TWMSize);
begin
  inherited;
  Invalidate;
end;procedure TSkinScrollBox.WMVScroll(var Message: TWMVScroll);
begin
  Inherited;
  Invalidate;
end;end.

Answer 2

unit SkinScrollBox;interfaceuses
  Windows,SysUtils,Classes,Controls,Forms,GdiPlus,Messages,Graphics,Types;
type
  TSkinScrollBox=class(TScrollBox)
  private
    FBufferBitmap:TBitmap;
  protected
    procedure WMEraseBkGnd(var Message:TWMEraseBkGnd);message WM_ERASEBKGND;
    procedure WMHScroll(var Message: TWMHScroll); message WM_HSCROLL;
    procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
    procedure PaintWindow(DC: HDC); override;
    procedure WMSize(var Message: TWMSize); message WM_SIZE;
  public
    constructor Create(AOwner:TComponent);override;
    destructor Destroy;override;
  published
    property Align;
    property Anchors;
    property AutoScroll;
    property AutoSize;
    property BevelEdges;
    property BevelInner;
    property BevelOuter;
    property BevelKind;
    property BevelWidth;
    property BiDiMode;
    property BorderStyle;
    property Constraints;
    property DockSite;
    property DoubleBuffered;
    property DragCursor;
    property DragKind;
    property DragMode;
    property Enabled;
    property Color;
    property Ctl3D;
    property Font;
    property Padding;
    property ParentBiDiMode;
    property ParentBackground default False;
    property ParentColor;
    property ParentCtl3D;
    property ParentDoubleBuffered;
    property ParentFont;
    property ParentShowHint;
    property PopupMenu;
    property ShowHint;
    property TabOrder;
    property TabStop;
    property Touch;
    property Visible;
    property OnCanResize;
    property OnClick;
    property OnConstrainedResize;
    property OnContextPopup;
    property OnDblClick;
    property OnDockDrop;
    property OnDockOver;
    property OnDragDrop;
    property OnDragOver;
    property OnEndDock;
    property OnEndDrag;
    property OnEnter;
    property OnExit;
    property OnGesture;
    property OnGetSiteInfo;
    property OnMouseActivate;
    property OnMouseDown;
    property OnMouseEnter;
    property OnMouseLeave;
    property OnMouseMove;
    property OnMouseUp;
    property OnMouseWheel;
    property OnMouseWheelDown;
    property OnMouseWheelUp;
    property OnResize;
    property OnStartDock;
    property OnStartDrag;
    property OnUnDock;
  end;procedure Register;implementationprocedure Register;
begin
  RegisterComponents('SkinEngine',[TSkinScrollBox]);
end;{ TSkinScrollBox }constructor TSkinScrollBox.Create(AOwner: TComponent);
begin
  inherited;
  FBufferBitmap:=TBitmap.Create;
end;destructor TSkinScrollBox.Destroy;
begin
  FBufferBitmap.Free;
  inherited;
end;procedure TSkinScrollBox.PaintWindow(DC: HDC);
var
  Brush:IGpLinearGradientBrush;
  Graphics:IGPGraphics;
  ClientWidth,ClientHeight:Integer;
  GPRect:TGPRect;
begin
  if (Height=0) or (Width=0) then Exit;
  ClientWidth:=RectWidth(ClientRect);
  ClientHeight:=RectHeight(ClientRect);
  if (ClientHeight<>Self.FBufferBitmap.Height)
    or (ClientWidth<>Self.FBufferBitmap.Width) then
  begin
    Self.FBufferBitmap.SetSize(ClientWidth,ClientHeight);
    Graphics:=TGPGraphics.Create(Self.FBufferBitmap.Canvas.Handle);
    GPRect:=TGPRect.Create(ClientRect);
    Brush:=TGpLinearGradientBrush.Create(GPRect,
              TGPColor.Blue,
              TGPColor.Gray,
              TGPLinearGradientMode.LinearGradientModeVertical);
    Graphics.FillRectangle(Brush,GPRect);
  end;
  BitBlt(DC,0,0,ClientWidth,ClientHeight,
        Self.FBufferBitmap.Canvas.Handle,0,0,SRCCOPY);
end;procedure TSkinScrollBox.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  Message.Result:=1;
end;procedure TSkinScrollBox.WMHScroll(var Message: TWMHScroll);
begin
  Inherited;
  Invalidate;
end;procedure TSkinScrollBox.WMPaint(var Message: TWMPaint);
begin
  ControlState:=ControlState+[csCustomPaint];
  inherited;
  ControlState:=ControlState-[csCustomPaint];
end;procedure TSkinScrollBox.WMSize(var Message: TWMSize);
begin
  inherited;
  Invalidate;
end;procedure TSkinScrollBox.WMVScroll(var Message: TWMVScroll);
begin
  Inherited;
  Invalidate;
end;end.

Answer 3

几点想法：
出现楼主的情况是因为滚动条滚动之后没有重绘客户区所导致,
一可能是楼主从没编写过控件，
还有一个可能是楼主没有看过TScrollBox及其父类TScrollingWinControl的代码，懒所导致，
楼主的控件在三种情况下需要重绘，一个拖动过大小，还有就是垂直和水平滚动条滚动之后，
需要在三个消息的事件处理中进行手动重绘，WM_SIZE,WM_HSCROLL,WM_WSCROLL这三个消息我贴的最后一份是加入了双缓冲的，提高绘制效率的

Answer 4

谢谢楼上高人，的确是刚用Delphi写东西，呵呵我只重写了WM_Paint现不是说本身的事件，而是其被动的接收WM_Paint消息，重绘自身的时候因为原来的还在上面，但WM_Paint会全部重新，导至部分效果不对……就是怎么样擦除原来绘制的效果，恢复原来的样子了，呵呵

Answer 5

上面的贴图很明了，对比一下左边的是正常绘制的右边的，下半部分正常，因为下半部分，被滚到不可见的地方后，再滚动出来,这样，整个控件会重绘，下半部是无效域，重绘后正常！但上半部分，实际上被绘制了两次，造成效果异常！所以，问题在于，在重绘时（WM_Paint消息处理中），怎么样强制清除原来的效果……再次感谢……

Answer 6

网上找了好多资料，难道要 自己处理 WM_ERASEBKGND 消息？？？？？
关键怎么处理呢……