Delphi7，按向上键时进行形状​​跳跃

我想在玩家按下UP键时进行形状​​跳跃，所以我能想到的最好的就是这个，但我使用的方法很糟糕并且有问题：

（形状坐标：shape1.top:=432；）

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
case key of
vk_up: shape1.top:=shape1.top-40   //so that it jumps to 392
end; 
end;

现在这个计时器：

procedure TForm1.Timer1Timer(Sender: TObject);
begin
timer1.interval:=300
if shape1.Top<400 then      //if shape1.top=392 < 400
begin
shape1.Top:=432;            //move back to 432
end;

end;

问题是玩家可以不断地按UP键，这是我不想要的。我知道这种方法很糟糕，所以我希望你有比这更好的方法，如果你能与我分享，我将不胜感激。

这是一个在恒定力场（例如，靠近地球表面的重力场）中弹跳的球。侧壁和地板是弹跳表面。您可以使用箭头键添加额外的力：

unit Unit5;

interface

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

type
  TRealVect = record
    X, Y: real;
  end;

const
  ZeroVect: TRealVect = (X: 0; Y: 0);

type
  TForm5 = class(TForm)
    Timer1: TTimer;
    procedure FormPaint(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
    procedure FormKeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);
  private
    { Private declarations }
    function ACC: TRealVect;
  const
    RADIUS = 16;
    DAMPING = 0.8;
    DT = 0.2;
    GRAVITY: TRealVect = (X: 0; Y: 10);
  var
    FForce: TRealVect;
    FPos: TRealVect;
    FVel: TRealVect;
  public
    { Public declarations }
  end;

var
  Form5: TForm5;

implementation

{$R *.dfm}

function RealVect(X, Y: real): TRealVect;
begin
  result.X := X;
  result.Y := Y;
end;

function Add(A, B: TRealVect): TRealVect;
begin
  result.X := A.X + B.X;
  result.Y := A.Y + B.Y;
end;

function Scale(A: TRealVect; C: real): TRealVect;
begin
  result.X := C*A.X;
  result.Y := C*A.Y;
end;

function TForm5.ACC: TRealVect;
begin
  result := Add(GRAVITY, FForce);
end;

procedure TForm5.FormCreate(Sender: TObject);
begin
  FPos := RealVect(Width div 2, 10);
  FVel := RealVect(0, 0);
end;

procedure TForm5.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  case Key of
    VK_UP:
      FForce := RealVect(0, -20);
    VK_DOWN:
      FForce := RealVect(0, 10);
    VK_RIGHT:
      FForce := RealVect(10, 0);
    VK_LEFT:
      FForce := RealVect(-10, 0);
  end;
end;

procedure TForm5.FormKeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  FForce := ZeroVect;
end;

procedure TForm5.FormPaint(Sender: TObject);
begin
  Canvas.Brush.Color := clRed;
  Canvas.Ellipse(round(FPos.X - RADIUS), round(FPos.Y - RADIUS),
    round(FPos.X + RADIUS), round(FPos.Y + RADIUS));
end;

procedure TForm5.Timer1Timer(Sender: TObject);
begin
  FVel := Add(FVel, Scale(ACC, DT));
  FPos := Add(FPos, Scale(FVel, DT));
  if FPos.Y + RADIUS >= ClientHeight then
  begin
    FVel.Y := -DAMPING*FVel.Y;
    FPos.Y := ClientHeight - RADIUS - 1;
  end;
  if FPos.X - RADIUS <= 0 then
  begin
    FVel.X := -DAMPING*FVel.X;
    FPos.X := RADIUS + 1;
  end;
  if FPos.X + RADIUS >= ClientWidth then
  begin
    FVel.X := -DAMPING*FVel.X;
    FPos.X := ClientWidth - RADIUS - 1;
  end;
  Invalidate;
end;

end.

将定时器的时间间隔设置为30， 照常'。

编译示例EXE http://privat.rejbrand.se/bounceball.exe