再学 GDI+[86]: TGPImage(6) - 拖动图像

本例效果图:

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代码文件:

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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:\temp\test.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.


 
   

窗体文件:

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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