再學 GDI+[83]: TGPImage(3) - 平行四邊形變換

　本例效果圖:

　　代碼文件: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:temptest.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);
　{第一點: 右上角; 第二點: 左上角; 第三點: 右下角; 第四點將根據平行四邊形計算; 只能是三個點.}
　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.窗體文件: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