把位图转化为图标

http://www.txsz.net/xs/delphi/1/NewTopic253.htm
You must create two bitmaps, a mask bitmap (called the "AND"
bitmap) and a image bitmap (called the XOR bitmap). You can pass the
handles to the "AND" and "XOR"  bitmaps to the Windows API function
CreateIconIndirect() and use the returned icon handle in your
application.

Example:

procedure TForm1.Button1Click(Sender: TObject);
var
  IconSizeX : integer;
  IconSizeY : integer;
  AndMask : TBitmap;
  XOrMask : TBitmap;
  IconInfo : TIconInfo;
  Icon : TIcon;
begin
 {Get the icon size}
  IconSizeX := GetSystemMetrics(SM_CXICON);
  IconSizeY := GetSystemMetrics(SM_CYICON);

 {Create the "And" mask}
  AndMask := TBitmap.Create;
  AndMask.Monochrome := true;
  AndMask.Width := IconSizeX;
  AndMask.Height := IconSizeY;

 {Draw on the "And" mask}
  AndMask.Canvas.Brush.Color := clWhite;
  AndMask.Canvas.FillRect(Rect(0, 0, IconSizeX, IconSizeY));
  AndMask.Canvas.Brush.Color := clBlack;
  AndMask.Canvas.Ellipse(4, 4, IconSizeX - 4, IconSizeY - 4);

 {Draw as a test}
  Form1.Canvas.Draw(IconSizeX * 2, IconSizeY, AndMask);

 {Create the "XOr" mask}
  XOrMask := TBitmap.Create;
  XOrMask.Width := IconSizeX;
  XOrMask.Height := IconSizeY;

 {Draw on the "XOr" mask}
  XOrMask.Canvas.Brush.Color := ClBlack;
  XOrMask.Canvas.FillRect(Rect(0, 0, IconSizeX, IconSizeY));
  XOrMask.Canvas.Pen.Color := clRed;
  XOrMask.Canvas.Brush.Color := clRed;
  XOrMask.Canvas.Ellipse(4, 4, IconSizeX - 4, IconSizeY - 4);

 {Draw as a test}
  Form1.Canvas.Draw(IconSizeX * 4, IconSizeY, XOrMask);

 {Create a icon}
  Icon := TIcon.Create;
  IconInfo.fIcon := true;
  IconInfo.xHotspot := 0;
  IconInfo.yHotspot := 0;
  IconInfo.hbmMask := AndMask.Handle;
  IconInfo.hbmColor := XOrMask.Handle;
  Icon.Handle := CreateIconIndirect(IconInfo);

 {Destroy the temporary bitmaps}
  AndMask.Free;
  XOrMask.Free;

 {Draw as a test}
  Form1.Canvas.Draw(IconSizeX * 6, IconSizeY, Icon);

 {Assign the application icon}
  Application.Icon := Icon;

 {Force a repaint}
  InvalidateRect(Application.Handle, nil, true);

 {Free the icon}
  Icon.Free;
end;