再學 GDI+[86]: TGPImage(6) - 拖動圖像

　本例效果圖:

　　代碼文件:unit Unit1;
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);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses GDIPOBJ, GDIPAPI;
var
　img: TGPImage;
　rt: TRect;
　flag: Boolean;
　x1,y1: Integer;
procedure TForm1.FormCreate(Sender: TObject);
const
　ImgPath = 'c:temptest.png';
var
　w,h: Integer;
begin
　if not FileExists(ImgPath) then Exit;
　img := TGPImage.Create(ImgPath);
　w := img.GetWidth;
　h := img.GetHeight;
　rt.Left := (ClIEntWidth - w) div 2;
　rt.Top := (ClIEntHeight - h) div 2;
　rt.Right := rt.Left + w;
　rt.Bottom := rt.Top + h;
　DoubleBuffered := True;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
　img.Free;
end;
procedure TForm1.FormPaint(Sender: TObject);
var
　g: TGPGraphics;
begin
　g := TGPGraphics.Create(Canvas.Handle);
　g.DrawImage(img, MakeRect(rt.Left, rt.Top, img.GetWidth, img.GetHeight));
　g.Free;
end;
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　if PtInRect(rt, Point(X,Y)) then
　begin
　　x1 := X;
　　y1 := Y;
　　flag := True;
　end;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
　Y: Integer);
begin
　if not flag then Exit;
　OffsetRect(rt, X-x1, Y-y1);
　x1 := X;
　y1 := Y;
　Repaint;
end;
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　flag := False;
end;
end.窗體文件:object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClIEntHeight = 190
　ClIEntWidth = 317
　Color = clBtnFace
　Font.Charset = DEFAULT_CHARSET
　Font.Color = clWindowText
　Font.Height = -11
　Font.Name = 'Tahoma'
　Font.Style = []
　OldCreateOrder = False
　Position = poDesktopCenter
　OnCreate = FormCreate
　OnDestroy = FormDestroy
　OnMouseDown = FormMouseDown
　OnMouseMove = FormMouseMove
　OnMouseUp = FormMouseUp
　OnPaint = FormPaint
　PixelsPerInch = 96
　TextHeight = 13
end