Delphi7, take a form jump when you press the Up key

Question

I would like to take a form jump when the player presses the UP key, so the best thing I can think of is that, but the method I used is terrible and problematic:

(form coordinates: 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; 

And now this timer:

 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; 

The problem is that players can constantly press the UP key, which I don’t want. I know this method is terrible, so I hope you have something better than this, and I would appreciate it if you could share it with me.

Answer 1

If the player can hold the key and KeyDown is triggered repeatedly, you can block it.

First declare a field in the form called FKeyLock: set of byte . (Note: this method will not succeed if you get Key values ​​above 255, but those that you are likely to handle will not be so high.)

 procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState); begin if key in FKeyLock then Exit; case key of vk_up: begin shape1.top:=shape1.top-40; //so that it jumps to 392 include(FKeyLock, vk_up); end; end; end; procedure TForm1.FormKeyUp(Sender: TObject; var Key: Word; Shift: TShiftState); begin exclude(FKeyLock, key); end; 

Answer 2

Here the ball bounces in a constant force field (for example, a gravitational field close to the surface of the Earth). Side walls and floor are bouncing surfaces. You can add extra strength using the arrow keys:

 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 := AX + BX; result.Y := AY + BY; end; function Scale(A: TRealVect; C: real): TRealVect; begin result.X := C*AX; result.Y := C*AY; 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. 

Set the timer interval to 30 as "normal".

Compiled Sample EXE