WM_ERASEBKGND官方解释（翻译），以及Delphi里所有的使用情况（就是绘制窗口控件背景色，并阻止进一步传递消息）

  TWMEraseBkgnd = packed record
    Msg: Cardinal;
    DC: HDC;
    Unused: Longint;
    Result: Longint;
  end;

procedure TWinControl.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  with ThemeServices do
  if ThemesEnabled and Assigned(Parent) and (csParentBackground in FControlStyle) then
    begin
      { Get the parent to draw its background into the control's background. }
      DrawParentBackground(Handle, Message.DC, nil, False);
    end
    else
    begin
      { Only erase background if we're not doublebuffering or painting to memory. }
      if not FDoubleBuffered or
         (TMessage(Message).wParam = TMessage(Message).lParam) then
        FillRect(Message.DC, ClientRect, FBrush.Handle);
    end;

  Message.Result := 1; // 相当于说，WM_ERASEBKGND的传递到此为止，无论如何都不要继续传递了
end;
procedure TWinControl.WMPaint(var Message: TWMPaint);
var
  DC, MemDC: HDC;
  MemBitmap, OldBitmap: HBITMAP;
  PS: TPaintStruct;
begin
  if not FDoubleBuffered or (Message.DC <> 0) then
  begin
    if not (csCustomPaint in ControlState) and (ControlCount = 0) then
      inherited
    else
      PaintHandler(Message);
  end
  else
  begin
    DC := GetDC(0); // 整个屏幕的DC，借用一下而已
    MemBitmap := CreateCompatibleBitmap(DC, ClientRect.Right, ClientRect.Bottom); // 图像不宜过大，所以设置成最大就是屏幕大小
    ReleaseDC(0, DC); // 还掉了
    MemDC := CreateCompatibleDC(0);
    OldBitmap := SelectObject(MemDC, MemBitmap);
    try
      DC := BeginPaint(Handle, PS); // 重新取得当前控件的DC
      Perform(WM_ERASEBKGND, MemDC, MemDC); // 结合上面的TWinControl.WMEraseBkgnd，可以观察到，要得就是这种效果，即双缓冲第一次绘制时候，需要删除背景
      Message.DC := MemDC; // 构建一个消息，把MemDC传入，当前控件和子控件都在MemDC上画，不在原先的DC上作画了
      WMPaint(Message); // 递归调用，会引发DC<>0的情况，从而正常绘制所有子控件（绘制子控件不需要双缓冲了），否则根本据不会进入绘制子控件的流程
      Message.DC := 0;  // 子控件绘制完毕，不管后续消息流动到何处，不要在消息包含的DC上绘制东西了
      BitBlt(DC, 0, 0, ClientRect.Right, ClientRect.Bottom, MemDC, 0, 0, SRCCOPY); // 把MemDC上的内容拷贝到DC上
      EndPaint(Handle, PS);
    finally
      SelectObject(MemDC, OldBitmap); // 还掉
      DeleteDC(MemDC); // 还掉
      DeleteObject(MemBitmap); // 还掉
    end;
  end;
end;

// Draws the windowed control to a device context.
procedure TWinControl.PaintTo(DC: HDC; X, Y: Integer);
var
  I, EdgeFlags, BorderFlags, SaveIndex: Integer;
  R: TRect;
begin
  Include(FControlState, csPaintCopy);
  SaveIndex := SaveDC(DC);
  MoveWindowOrg(DC, X, Y);
  IntersectClipRect(DC, 0, 0, Width, Height);
  BorderFlags := 0;
  EdgeFlags := 0;
  if GetWindowLong(Handle, GWL_EXSTYLE) and WS_EX_CLIENTEDGE <> 0 then
  begin
    EdgeFlags := EDGE_SUNKEN;
    BorderFlags := BF_RECT or BF_ADJUST
  end else
  if GetWindowLong(Handle, GWL_STYLE) and WS_BORDER <> 0 then
  begin
    EdgeFlags := BDR_OUTER;
    BorderFlags := BF_RECT or BF_ADJUST or BF_MONO;
  end;
  if BorderFlags <> 0 then
  begin
    SetRect(R, 0, 0, Width, Height);
    DrawEdge(DC, R, EdgeFlags, BorderFlags);
    MoveWindowOrg(DC, R.Left, R.Top);
    IntersectClipRect(DC, 0, 0, R.Right - R.Left, R.Bottom - R.Top);
  end;
  Perform(WM_ERASEBKGND, DC, 0);
  Perform(WM_PAINT, DC, 0);
  if FWinControls <> nil then
    for I := 0 to FWinControls.Count - 1 do
      with TWinControl(FWinControls[I]) do
        if Visible then PaintTo(DC, Left, Top);
  RestoreDC(DC, SaveIndex);
  Exclude(FControlState, csPaintCopy);
end;

procedure PerformEraseBackground(Control: TControl; DC: HDC);
var
  LastOrigin: TPoint;
begin
  GetWindowOrgEx(DC, LastOrigin);
  SetWindowOrgEx(DC, LastOrigin.X + Control.Left, LastOrigin.Y + Control.Top, nil);
  Control.Parent.Perform(WM_ERASEBKGND, Integer(DC), Integer(DC)); // TSpeedButton自己不是Windows窗口，只能出此下策
  SetWindowOrgEx(DC, LastOrigin.X, LastOrigin.Y, nil);
end;

procedure TSpeedButton.Paint;
const
  DownStyles: array[Boolean] of Integer = (BDR_RAISEDINNER, BDR_SUNKENOUTER);
  FillStyles: array[Boolean] of Integer = (BF_MIDDLE, 0);
var
  PaintRect: TRect;
  DrawFlags: Integer;
  Offset: TPoint;
  Button: TThemedButton;
  ToolButton: TThemedToolBar;
  Details: TThemedElementDetails;
begin
  if not Enabled then
  begin
    FState := bsDisabled;
    FDragging := False;
  end
  else if FState = bsDisabled then
    if FDown and (GroupIndex <> 0) then
      FState := bsExclusive
    else
      FState := bsUp;
  Canvas.Font := Self.Font;

  if ThemeServices.ThemesEnabled then
  begin
    PerformEraseBackground(Self, Canvas.Handle);
    // 其它代码
  end;
end;

procedure TCustomForm.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if not IsIconic(Handle) then inherited else
  begin
    Message.Msg := WM_ICONERASEBKGND; // 当窗口处于最小化状态的时候，改变消息值
    DefaultHandler(Message); // 当窗口是MDI时，还应该改变当前窗口的图标，否则相当于不执行
  end;
end;

procedure TCustomForm.ClientWndProc(var Message: TMessage);

  procedure Default;
  begin
    with Message do
      Result := CallWindowProc(FDefClientProc, ClientHandle, Msg, wParam, lParam);
  end;

  function MaximizedChildren: Boolean;
  var
    I: Integer;
  begin
    for I := 0 to MDIChildCount - 1 do
      if MDIChildren[I].WindowState = wsMaximized then
      begin
        Result := True;
        Exit;
      end;
    Result := False;
  end;

var
  DC: HDC;
  PS: TPaintStruct;
  R: TRect;
begin
  with Message do
    case Msg of
      WM_NCHITTEST:
        begin
          Default;
          if Result = HTCLIENT then Result := HTTRANSPARENT;
        end;
      WM_ERASEBKGND:
        begin
          FillRect(TWMEraseBkGnd(Message).DC, ClientRect, Brush.Handle);
          { Erase the background at the location of an MDI client window }
          if (FormStyle = fsMDIForm) and (FClientHandle <> 0) then
          begin
            Windows.GetClientRect(FClientHandle, R);
            FillRect(TWMEraseBkGnd(Message).DC, R, Brush.Handle);
          end;
          Result := 1;
        end;
      $3F://!
        begin
          Default;
          if FFormStyle = fsMDIForm then
            ShowMDIClientEdge(FClientHandle, (MDIChildCount = 0) or
              not MaximizedChildren);
        end;
      WM_PAINT:
        begin
          DC := TWMPaint(Message).DC;
          if DC = 0 then
            TWMPaint(Message).DC := BeginPaint(ClientHandle, PS);
          try
            if DC = 0 then
            begin
              GetWindowRect(FClientHandle, R);
              R.TopLeft := ScreenToClient(R.TopLeft);
              MoveWindowOrg(TWMPaint(Message).DC, -R.Left, -R.Top);
            end;
            PaintHandler(TWMPaint(Message));
          finally
            if DC = 0 then
              EndPaint(ClientHandle, PS);
          end;
        end;
    else
      Default;
    end;
end;

procedure TCustomForm.DefaultHandler(var Message);
begin
  if ClientHandle <> 0 then
    with TMessage(Message) do
      if Msg = WM_SIZE then
        Result := DefWindowProc(Handle, Msg, wParam, lParam) else
        Result := DefFrameProc(Handle, ClientHandle, Msg, wParam, lParam)
  else
    inherited DefaultHandler(Message)
end;

// 处理图标消息 message WM_ICONERASEBKGND
procedure TCustomForm.WMIconEraseBkgnd(var Message: TWMIconEraseBkgnd); 
begin
  if FormStyle = fsMDIChild then
  if (FormStyle = fsMDIChild) and not (csDesigning in ComponentState) then
    FillRect(Message.DC, ClientRect, Application.MainForm.Brush.Handle)
  else inherited;
end;

procedure TApplication.WndProc(var Message: TMessage);
var
  procedure Default;
  begin
    with Message do
      Result := DefWindowProc(FHandle, Msg, WParam, LParam);
  end;

begin
  try
    Message.Result := 0;
    for I := 0 to FWindowHooks.Count - 1 do
      if TWindowHook(FWindowHooks[I]^)(Message) then Exit;
    CheckIniChange(Message);
    with Message do
      case Msg of
        WM_SYSCOMMAND:
          case WParam and $FFF0 of
            SC_MINIMIZE: Minimize;
            SC_RESTORE: Restore;
          else
            Default;
          end;
        WM_CLOSE:
          if MainForm <> nil then MainForm.Close;
        WM_PAINT:
          if IsIconic(FHandle) then DrawAppIcon else Default;
        WM_ERASEBKGND: // 改变消息，然后转发
          begin
            Message.Msg := WM_ICONERASEBKGND;
            Default;
          end;
        WM_NULL:
          CheckSynchronize;
      else
        Default;
      end;
  except
    HandleException(Self);
  end;
end;

procedure TCustomComboBox.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if Style = csSimple then
  begin
    FillRect(Message.DC, ClientRect, Parent.Brush.Handle);
    Message.Result := 1;
  end
  else
    DefaultHandler(Message);
end;

procedure TButtonControl.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  { Under theme services the background is drawn in CN_CTLCOLORSTATIC. }
  if ThemeServices.ThemesEnabled then
    Message.Result := 1
  else
    inherited;
end;

procedure TButton.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if ThemeServices.ThemesEnabled then
    Message.Result := 1
  else
    DefaultHandler(Message);
end;

procedure TScrollBar.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  DefaultHandler(Message);
end;

procedure TCustomControlBar.WMEraseBkgnd(var Message: TWmEraseBkgnd);
var
  R: TRect;
  I, J: Integer;
  Save: Boolean;
begin
  if Message.DC <> 0 then
    Canvas.Handle := Message.DC;
  if Picture.Graphic <> nil then
  begin

    try
      R := ClientRect;
      Save := FDrawing;
      FDrawing := True;
      try
        { Tile image across client area }
        for I := 0 to (R.Right - R.Left) div Picture.Width do
          for J := 0 to (R.Bottom - R.Top) div Picture.Height do
            Canvas.Draw(I * Picture.Width, J * Picture.Height, Picture.Graphic);
      finally
        FDrawing := Save;
      end
    finally
      if Message.DC <> 0 then
        Canvas.Handle := 0;
      Message.Result := 1;
    end;
  end
  else
  begin
    Canvas.Brush.Color := Color;
    Canvas.Brush.Style := bsSolid;
    Canvas.FillRect(ClientRect);
    inherited;
  end;
end;

procedure TDBCtrlPanel.WMEraseBkgnd(var Message: TMessage);
begin
  Message.Result := 1;
end;

procedure TDBCtrlGrid.WMEraseBkgnd(var Message: TMessage);
begin
  Message.Result := 1;
end;procedure TDBMemo.WMPaint(var Message: TWMPaint);
var
  S: string;
begin
  if not (csPaintCopy in ControlState) then inherited else
  begin
    if FDataLink.Field <> nil then
      if FDataLink.Field.IsBlob then
      begin
        if FAutoDisplay then
          S := AdjustLineBreaks(FDataLink.Field.AsString) else
          S := Format('(%s)', [FDataLink.Field.DisplayLabel]);
      end else
        S := FDataLink.Field.DisplayText;
    SendMessage(FPaintControl.Handle, WM_SETTEXT, 0, Integer(PChar(S)));
    SendMessage(FPaintControl.Handle, WM_ERASEBKGND, Message.DC, 0);
    SendMessage(FPaintControl.Handle, WM_PAINT, Message.DC, 0);
  end;
end;

procedure TShadowWindow.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  Message.Result := 0;
end;

procedure TTabSet.Paint;
var
  TabStart, LastTabPos: Integer;
  TabPos: TTabPos;
  Tab: Integer;
  Leading: TEdgeType;
  Trailing: TEdgeType;
  isFirst, isLast, isSelected, isPrevSelected: Boolean;
  R: TRect;
begin
  if not HandleAllocated then Exit;

  MemBitmap.Canvas.Font := Self.Canvas.Font;

  { draw background of tab area }
  with MemBitmap.Canvas do
  begin
    Brush.Bitmap := BrushBitmap;
    if ThemeServices.ThemesEnabled and ParentBackground then
      Perform(WM_ERASEBKGND, MemBitmap.Canvas.Handle, 0)
    else
      FillRect(Rect(0, 0, MemBitmap.Width, MemBitmap.Height));

  end;
end;

procedure TOleControl.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if FMiscStatus and OLEMISC_INVISIBLEATRUNTIME = 0 then
    DefaultHandler(Message) else
    inherited;
end;

procedure TPageControl.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  if (not ThemeServices.ThemesEnabled) or (not ParentBackground) then
    inherited
  else
    Message.Result := 1;
end;

procedure TCustomStatusBar.WMEraseBkGnd(var Message: TWMEraseBkGnd);
var
  Details: TThemedElementDetails;
begin
  if ThemeServices.ThemesEnabled then
  begin
    Details := ThemeServices.GetElementDetails(tsStatusRoot);
    ThemeServices.DrawElement(Message.DC, Details, ClientRect, nil);
    Message.Result := 1;
  end
  else
    inherited;
end;

procedure TTrackBar.WMEraseBkGnd(var Message: TWMEraseBkGnd);
var
  R: TRect;
begin
  if ThemeServices.ThemesEnabled then
  begin
    R := ClientRect;
    if Focused and ((Perform(WM_QUERYUISTATE, 0, 0) and UISF_HIDEFOCUS) = 0) then
      InflateRect(R, -1, -1);
    ThemeServices.DrawParentBackground(Handle, Message.DC, nil, False, @R);
    Message.Result := 1;
  end
  else
    inherited;
end;

procedure TToolBar.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if not Transparent then
    inherited else
    DefaultHandler(Message);
end;

procedure TCoolBar.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if not ThemeServices.ThemesEnabled and (IsBackgroundDirty or (IsAutoSized and (Bands.Count = 0))) then
    inherited;
  DefaultHandler(Message);
end;

procedure TCustomListView.WndProc(var Message: TMessage);
begin
  if not (csDesigning in ComponentState) and ((Message.Msg = WM_LBUTTONDOWN) or
    (Message.Msg = WM_LBUTTONDBLCLK)) and not Dragging and (DragMode = dmAutomatic) then
  begin
    if not IsControlMouseMsg(TWMMouse(Message)) then
    begin
      ControlState := ControlState + [csLButtonDown];
      Dispatch(Message);
    end;
  end
  else if not (((Message.Msg = WM_PAINT) or (Message.Msg = WM_ERASEBKGND)) and
    Items.FNoRedraw) then
    inherited WndProc(Message);
end;

procedure TCoolBar.PaintWindow(DC: HDC);
begin
  Perform(WM_ERASEBKGND, DC, 0);
  inherited;
end;