再学GDI+[88]: TGPImage(8)

本例效果图:

代码文件:unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls;
type
　TForm1 = class(TForm)
　　CheckBox1: TCheckBox;
　　procedure FormCreate(Sender: TObject);
　　procedure FormDestroy(Sender: TObject);
　　procedure FormPaint(Sender: TObject);
　　procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses GDIPOBJ, GDIPAPI;
var
　img: TGPImage;
　rt: TGPRectF;
　n: Single = 2.0; {放大的倍数}
procedure TForm1.FormCreate(Sender: TObject);
begin
　img := TGPImage.Create('c:\temp\test.png');
　ClientWidth := img.GetWidth;
　ClientHeight := img.GetHeight;
　Position := poDesktopCenter;
　DoubleBuffered := True;
　CheckBox1.Caption := '使用放大镜';
　CheckBox1.Left := ClientWidth - CheckBox1.Width;
　CheckBox1.Top := ClientHeight - CheckBox1.Height - 2;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
　img.Free;
end;
procedure TForm1.FormPaint(Sender: TObject);
var
　g: TGPGraphics;
　p: TGPPen;
　b: TGPSolidBrush;
begin
　g := TGPGraphics.Create(Canvas.Handle);
　p := TGPPen.Create(MakeColor(128, 255, 255, 255));
　b := TGPSolidBrush.Create(aclBlack);
　{原图像}
　g.DrawImage(img, 0, 0, img.GetWidth, img.GetHeight);
　if CheckBox1.Checked then
　begin
　　{放大镜的阴影}
　　g.FillRectangle(b, MakeRect(rt.X + 2, rt.Y + 2, rt.Width, rt.Height));
　　{放大后的局部图像: 参数2是放大后的范围; 参数3-6是要被放大的范围; 参数7是单位}
　　g.DrawImage(img, rt, rt.X, rt.Y, rt.Width / n, rt.Height / n, UnitPixel);
　　{放大镜的边框}
　　g.DrawRectangle(p, rt);
　end;
　b.Free;
　p.Free;
　g.Free;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
　Y: Integer);
begin
　if CheckBox1.Checked then
　begin
　　rt := MakeRect(X, Y, 150.0, 150);
　　Repaint;
　end;
end;
end.

窗体文件:object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClientHeight = 206
　ClientWidth = 339
　Color = clBtnFace
　Font.Charset = DEFAULT_CHARSET
　Font.Color = clWindowText
　Font.Height = -11
　Font.Name = 'Tahoma'
　Font.Style = []
　OldCreateOrder = False
　OnCreate = FormCreate
　OnDestroy = FormDestroy
　OnMouseMove = FormMouseMove
　OnPaint = FormPaint
　PixelsPerInch = 96
　TextHeight = 13
　object CheckBox1: TCheckBox
　　Left = 240
　　Top = 181
　　Width = 97
　　Height = 17
　　Caption = 'CheckBox1'
　　TabOrder = 0
　end
end