GDI+ 圖片拖曳移動範例：滑鼠事件與 OffsetRect 實現

效果展示

極簡實現邏輯

• 記錄圖片矩形 rt、拖曳旗標 flag、按下座標 x1,y1
• OnMouseDown：命中 rt 內 → 設旗標、記錄座標
• OnMouseMove：旗標為真 → OffsetRect(rt, X-x1, Y-y1) 位移矩形 → 更新座標 → Repaint
• OnMouseUp：清旗標
• OnPaint：g.DrawImage(img, rt.Left, rt.Top, img.Width, img.Height)

完整代碼

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(...); begin if PtInRect(rt, Point(X,Y)) then begin x1:=X; y1:=Y; flag:=True; end; end;
procedure TForm1.FormMouseMove(...); begin if not flag then Exit; OffsetRect(rt, X-x1, Y-y1); x1:=X; y1:=Y; Repaint; end;
procedure TForm1.FormMouseUp(...); begin flag:=False; end;
end.