本例效果图:

---

代码文件:

---

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);
  private
    procedure RectToPoints;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI;

var
  img: TGPImage;
  flag: Integer = -1;
  ClickImg: Boolean;
  rt: TRect;
  pts: array[0..7] of TPoint;
  x1,y1: Integer;

{从矩形中获取八个点, 因要反复使用, 故提取为一个独立的过程}
procedure TForm1.RectToPoints;
begin
  pts[0] := rt.TopLeft;
  pts[1] := Point(rt.Left, rt.Top + (rt.Bottom - rt.Top) div 2);
  pts[2] := Point(rt.Left, rt.Bottom);
  pts[3] := Point(rt.Left + (rt.Right - rt.Left) div 2, rt.Bottom);;
  pts[4] := rt.BottomRight;
  pts[5] := Point(rt.Right, rt.Top + (rt.Bottom - rt.Top) div 2);;
  pts[6] := Point(rt.Right, rt.Top);;
  pts[7] := Point(rt.Left + (rt.Right - rt.Left) div 2, rt.Top);
end;

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;

  RectToPoints;

  DoubleBuffered := True;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  img.Free;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  p: TGPPen;
  i: Integer;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  p := TGPPen.Create(aclRed);
  g.DrawImage(img, MakeRect(rt));

  if ClickImg then
    for i := 0 to Length(pts) - 1 do
      g.DrawRectangle(p, MakeRect(pts[i].X - 3, pts[i].Y - 3, 6, 6));
  p.Free;
  g.Free;
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  i: Integer;
begin
  flag := -1;
  for i := 0 to Length(pts) - 1 do
    if PtInRect(Bounds(pts[i].X - 3, pts[i].Y - 3, 6, 6), Point(X, Y)) then
    begin
      flag := i;
      Break;
    end;
  if flag = -1 then
  begin
    ClickImg := PtInRect(rt, Point(X,Y));
    Repaint;
  end else begin
    x1 := X;
    y1 := Y;
  end;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if flag = -1 then Exit;
  case flag of
    0: begin Inc(rt.Left, X-x1); Inc(rt.Top, Y-y1) end;
    1: begin Inc(rt.Left, X-x1) end;
    2: begin Inc(rt.Left, X-x1); Inc(rt.Bottom, Y-y1) end;
    3: begin Inc(rt.Bottom, Y-y1) end;
    4: begin Inc(rt.Right, X-x1); Inc(rt.Bottom, Y-y1) end;
    5: begin Inc(rt.Right, X-x1) end;
    6: begin Inc(rt.Right, X-x1); Inc(rt.Top, Y-y1) end;
    7: begin Inc(rt.Top, Y-y1) end;
  end;
  x1 := X;
  y1 := Y;

  RectToPoints;
  Repaint;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  flag := -1;
end;

end.

---

窗体文件:

---

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 246
  ClientWidth = 346
  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
  onm ouseDown = FormMouseDown
  onm ouseMove = FormMouseMove
  onm ouseUp = FormMouseUp
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end