Delphi 经典游戏程序设计40例 的学习 例30 残留的轨迹是圆形运动

unit R30;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;

type
  TRei30 = class(TForm)
    Panel1: TPanel;
    Button1: TButton;
    ScrollBar1: TScrollBar;
    ScrollBar2: TScrollBar;
    ScrollBar3: TScrollBar;
    Edit1: TEdit;
    Edit2: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Image1: TImage;
    Timer1: TTimer;
    Edit3: TEdit;
    ScrollBar4: TScrollBar;
    Edit4: TEdit;
    Label4: TLabel;
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
    procedure ScrollBar1Change(Sender: TObject);
    procedure ScrollBar2Change(Sender: TObject);
    procedure ScrollBar3Change(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure ScrollBar4Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Rei30: TRei30;
  St : Byte;        //按钮控制，设置状态控制指示用变量
  XR,YR : Word;
  X,Y,DX,DY,DD,CY: Integer;   //X,Y 坐标用变量，DX,DY 坐标增量(变化量)用变量，
  TR,QTR,DR : Extended;          //DR  弧度的变化量，
  Col : TColor;
  RectD : TRect;



implementation

{$R *.dfm}

procedure TRei30.FormCreate(Sender: TObject);
begin   //设置初始值，

  DD := 10;
  XR := 60;
  YR := 60;
  CY := 1;
  Col := clYellow;
  ScrollBar1.Position := DD;
  ScrollBar2.Position := XR;
  ScrollBar3.Position := YR;
  ScrollBar4.Position := CY;
end;

procedure TRei30.Timer1Timer(Sender: TObject);
begin
  case St of
    0: begin
      RectD := Rect(0,0,Image1.Width,Image1.Height);
      Image1.Canvas.Brush.Color := clBlack;
      Image1.Canvas.FillRect(RectD);   //刷黑
      Edit1.Text := ' ' + IntToStr(DD) + '°'; //显示参数
      Edit2.Text := ' ' + IntToStr(XR);
      Edit3.Text := ' ' + IntToStr(YR);
      Edit4.Text := ' ' + IntToStr(CY);

      X := Image1.Width div 2;
      Y := 0;
      TR := - Pi / 2;
      DR := DD * Pi / 180;
      St := 1;
    end;

    1: begin
      QTR := TR;
      TR := TR + DR;
      DX := Round(XR * (Cos(TR) - Cos(QTR)));   //核心计算
      DY := Round(YR * (Sin(TR) - Sin(QTR)));
      X := X + DX;
      Y := Y + DY + CY;
      Image1.Canvas.Pixels[X,Y] := clRed;         //4点显示
      Image1.Canvas.Pixels[X + 1,Y] := clYellow;
      Image1.Canvas.Pixels[X,Y + 1] := clBlue;
      Image1.Canvas.Pixels[X + 1,Y + 1] := clGreen;
      if (Y > Image1.Height  + YR * 2) or (Y < -YR * 2) then
        begin
          St := 2;
          Edit1.Text := '绘图完成';
        end;


    end;
  end;
end;

procedure TRei30.ScrollBar1Change(Sender: TObject);
begin
  DD := ScrollBar1.Position;
  Edit1.Text := ' ' + IntToStr(DD) + '°';
  DR := Pi * DD / 180;                      //应该去掉这行，否则在绘图中会即时的改变
end;                                            //似乎又不行，在状态1中，W,DY值都被在计算
                                                // 所以这里只有同步重新计算DR值
procedure TRei30.ScrollBar2Change(Sender: TObject);
begin
   XR := ScrollBar2.Position;
   Edit2.Text := ' ' + IntToStr(XR);
end;

procedure TRei30.ScrollBar3Change(Sender: TObject);
begin
  YR := ScrollBar3.Position;
  Edit3.Text := ' ' + IntToStr(YR);

end;

procedure TRei30.ScrollBar4Change(Sender: TObject);
begin
  CY := ScrollBar4.Position;
  Edit4.Text := ' ' + IntToStr(CY);

end;

procedure TRei30.Button1Click(Sender: TObject);
begin
  St := 0;
end;



end.

1，程序结构同前例

2，是对三角函数的应用，套用公式，不明白。