再学GDI+[4]: DrawEllipse

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 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
　x: Integer = 20;
　y: Integer = 20;
　w: Integer = 100;
　h: Integer = 50;
　f: Byte;
　a,b: Integer;
　p: TGPPen;
procedure TForm1.FormCreate(Sender: TObject);
begin
　p := TGPPen.Create(MakeColor(255,0,0), 2);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
　p.Free;
end;
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　f := 1;
　a := X;
　b := Y;
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
　Y: Integer);
begin
　if (f = 0) then Exit;
　if ssCtrl in Shift then
　begin
　　f := 2;
　　Text := 'Ctrl 键被按下, 鼠标可调整大小';
　end else Text := '没有按下 Ctrl 键, 鼠标可调整位置';
　a := X - a;
　b := Y - b;
　Repaint;
　a := X;
　b := Y;
end;
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　f := 0;
end;
procedure TForm1.FormPaint(Sender: TObject);
var
　g: TGPGraphics;
begin
　g := TGPGraphics.Create(Canvas.Handle);
　g.Clear(MakeColor(255,255,255));
　case f of
　　1: begin
　　　Inc(x,a);
　　　Inc(y,b);
　　end;
　　2: begin
　　　Inc(w,a);
　　　Inc(h,b);
　　end;
　end;
　g.DrawEllipse(p, x, y, w, h);
　g.Free;
end;
end.

窗体文件:

object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClientHeight = 176
　ClientWidth = 337
　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