再学 GDI+[4]: DrawEllipse - 绘制椭圆

本例效果图:

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代码文件:

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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:

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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