再学 GDI+[4]: DrawEllipse 绘制椭圆

本例效果图:

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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