你按下截图按钮的时候,其实看到的不是真正的桌面了,是程序把桌面的图片截下来画在一个全屏的窗口上.

我写个小程序给你参考一下。

unit unMainFrm;

interface

uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, ExtCtrls, StdCtrls;

type

TScreenCanvas = class(TCanvas)

protected

procedure CreateHandle; override;

public

destructor Destroy; override;

end;

TForm2 = class(TForm)

procedure FormMouseDown(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

procedure FormMouseUp(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);

procedure FormCreate(Sender: TObject);

procedure FormPaint(Sender: TObject);

procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);

private

{ Private declarations }

FBitMap: TBitmap;

FScreenCanvas: TScreenCanvas;

FDrawEnable: Boolean;

public

{ Public declarations }

end;

var

Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.FormCreate(Sender: TObject);

begin

FBitMap := TBitmap.Create;

with FBitMap do

begin

Width := 1024;

Height := 768;

end;

FScreenCanvas := TScreenCanvas.Create;

FBitMap.Canvas.CopyRect(Rect(0,0,1024,768), FScreenCanvas, Rect(0,0,1024,768));

end;

procedure TForm2.FormKeyDown(Sender: TObject; var Key: Word;

Shift: TShiftState);

begin

if Key = VK_ESCAPE then

Application.Terminate;

if Key = VK_CONTROL then

begin

Canvas.FillRect(Canvas.ClipRect);

Invalidate;

end;

end;

procedure TForm2.FormMouseDown(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

begin

FDrawEnable := True;

Randomize;

Canvas.Brush.Color := Random($FFFFFF + 1);

Ellipse(Canvas.Handle, X - 5, Y - 5, X + 5, Y + 5);

end;

procedure TForm2.FormMouseMove(Sender: TObject; Shift: TShiftState; X,

Y: Integer);

begin

if FDrawEnable then

begin

Ellipse(Canvas.Handle, X - 5, Y - 5, X + 5, Y + 5);

end;

end;

procedure TForm2.FormMouseUp(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

begin

FDrawEnable := False;

end;

procedure TForm2.FormPaint(Sender: TObject);

begin

Canvas.Draw(0, 0, FBitMap);

end;

{ TScreenCanvas }

procedure TScreenCanvas.CreateHandle;

begin

inherited;

Handle := GetDC(0);

end;

destructor TScreenCanvas.Destroy;

begin

ReleaseDC(Handle, 0);

inherited;

end;

end.

你改下单元名和窗体的名字就可以用了.

TScreenCanvas是用来获取桌面图像的类.

只要掌握CopyRect函数就没什么问题了，然后记录几个鼠标的点击位置就可以把图给截出来.图片的拉伸移动也是CopyRect函数搞的