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