本例效果图:
![](https://www.cnblogs.com/images/cnblogs_com/del/142973/o_8713.gif)
代码文件:
![](https://www.cnblogs.com/images/cnblogs_com/del/142973/o_8713.gif)
代码文件:
unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs; type TForm1 = class(TForm) procedure FormPaint(Sender: TObject); procedure FormCreate(Sender: TObject); procedure FormDestroy(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; pts: array[0..2] of TGPPoint; flag: Integer = -1; procedure TForm1.FormCreate(Sender: TObject); var w,h: Integer; begin img := TGPImage.Create('C:\temp\test.jpg'); w := img.GetWidth; h := img.GetHeight; pts[0] := MakePoint((ClientWidth - w) div 2 + w, (ClientHeight - h) div 2); pts[1] := MakePoint((ClientWidth - w) div 2, (ClientHeight - h) div 2); pts[2] := MakePoint((ClientWidth - w) div 2 + w, (ClientHeight - h) div 2 + h); DoubleBuffered := True; end; procedure TForm1.FormDestroy(Sender: TObject); begin img.Free; end; procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer); var i: Integer; begin for i := 0 to Length(pts) do if PtInRect(Bounds(pts[i].X-3, pts[i].Y-3, 6, 6), Point(X, Y)) then begin flag := i; Exit; end; end; procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer); begin if flag = -1 then Exit; pts[flag] := MakePoint(X, Y); Repaint; end; procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer); begin flag := -1; end; procedure TForm1.FormPaint(Sender: TObject); var g: TGPGraphics; p: TGPPen; i: Integer; begin g := TGPGraphics.Create(Self.Canvas.Handle); p := TGPPen.Create(aclRed); {第一点: 右上角; 第二点: 左上角; 第三点: 右下角; 第四点将根据平行四边形计算; 只能是三个点.} g.DrawImage(img, PGPPoint(@pts), Length(pts)); for i := 0 to Length(pts)-1 do g.DrawRectangle(p, pts[i].X-3, pts[i].Y-3, 6, 6); p.Free; g.Free; end; end.窗体文件:
object Form1: TForm1 Left = 0 Top = 0 Caption = 'Form1' ClientHeight = 206 ClientWidth = 307 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