(六)区域抓图窗体
创建一个新的Form1，保存为Capture1.pas。设置属性BorderIcons的四个属性为false.
BorderStyle设为bsNone,Cursor设为crCross,FormStyle设为fsStayOnTop.
添加一个私有变量：fDragging:Boolean;两个公共变量:fRect:TRect,fBmp:TBitmap;
Form1的作用：在区域抓图时创建，抓图后消失.

unit Capture1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    fDragging:Boolean;
  public
    fRect:TRect;
    fBmp:TBitmap;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var aDC:HDC;  //设备描述表的句柄
begin
  fBmp := TBitmap.Create ;
  fBmp.Width := Screen.Width ;
  fBmp.Height:= Screen.Height;
  aDC := GetDC(0); //获取一个窗口的设备描述表的句柄，0参数返回屏幕窗口设备描述表的句柄
  BitBlt(fBmp.Canvas.Handle,0,0,Screen.Width,Screen.Height,aDC,0,0,srcCopy);
  ReleaseDC(0,aDC,);
  SetBounds(0,0,Screen.Width,Screen.Height);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  fBmp.Free ;
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  Canvas.Draw(0,0,fBmp);  //将图形绘制到 Canvas
end;

//如果按下鼠标左键，用SetRect设置矩形fRect，使其只是一个点。
//用 DrawFocusRect 把这个矩形画出来
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button=mbLeft then begin
    fDragging:=true;
    SetRect(fRect,x,y,x,y);
    Canvas.DrawFocusRect(fRect);
  end;
end;

//鼠标移动时, 判断是否在画图中（按下鼠标左键），DrawFocusRect重新设置矩形
//使右下角为当前鼠标位置，在调用DrawFocusRect画出矩形
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if fDragging then begin
    Canvas.DrawFocusRect(fRect);
    fRect.Right := X ;
    fRect.Bottom:= Y ;
    Canvas.DrawFocusRect(fRect);
  end;
end;

//判断是否在画图中（按下鼠标左键），鼠标弹起时，
//DrawFocusRect重新设置矩形  .关闭窗体
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if fDragging then begin
    Canvas.DrawFocusRect(fRect);
    fDragging:=false;
  end;
  ModalResult:=mrOK;   //关闭窗体
end;

end.