Delphi, How to make a shape stop moving

Question

I am trying to make a shape move towards onother using 2 shapes and 2 timer, but i really can't seem. I was thinking:

At the beggining, I will make shape 1 calculate the distance of shape 2 and then move towards it, this is what i have done, i have also added comments to help you understand the code, because it is a little bit confusing:

procedure TForm1.Timer1Timer(Sender: TObject);
begin
timer1.Interval:=100;           //set interval=200
                            //begin
if shape1.Left=shape2.Left then
begin
shape1.Left:=shape1.left         //If shape's 1 coordinates = shape's 2 then
end else                        //shape1.left:=stop moving else do
begin                           //find if shape 2 is right or left from shape 1
if shape1.left>shape2.Left then
begin
shape1.Left:=shape1.Left-5;
end else shape1.Left:=shape1.Left+5;
//Moving to shape2.left until shape1.left:=shape2.left



end;
end;


procedure TForm1.Timer2Timer(Sender: TObject);
begin
timer2.Interval:=100;      //the same method as timer1

if shape1.top=shape2.top then
begin
shape1.top:=shape1.top
end else
begin
if shape1.top>shape2.top then
begin
shape1.top:=shape1.top-5;
end else shape1.top:=shape1.top+5;

end;
end;

end.

What shape1 does now is to move toward shape 2, but it doesn't stop moving, i mean it sticks to shape 2, but it is still moving upside-down, but not left-right from shape 2. I checked timer's 2 code and there is nothing wrong.

Answer 1

Try the following code (assign OnCreate and OnPaint of the form and set the timer to 30 millisecond intervals):

unit Unit5;

interface

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

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

  TForm5 = class(TForm)
    Timer1: TTimer;
    procedure FormPaint(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
    FPosA, FPosB: TVector;
    v: TVector;
  public
    { Public declarations }
  end;

var
  Form5: TForm5;

implementation

uses Math;

{$R *.dfm}

const RADIUS = 16;

function RealPoint(X, Y: real): TVector;
begin
  result.X := X;
  result.Y := Y;
end;

function RoundPoint(P: TVector): TPoint;
begin
  result.X := round(P.X);
  result.Y := round(P.Y);
end;

procedure TForm5.FormCreate(Sender: TObject);
var
  DX, DY: real;
begin
  FPosA := RealPoint(32, 32);
  FPosB := RealPoint(500, 200);

  DX := FPosB.X - FPosA.X;
  DY := FPosB.Y - FPosA.Y;

  v.X := DX / 100;
  v.Y := DY / 100;
end;

function EllipseRectFromPoint(P: TVector): TRect;
var
  ScreenPoint: TPoint;
begin
  ScreenPoint := RoundPoint(P);
  result.Left := ScreenPoint.X - RADIUS;
  result.Right := ScreenPoint.X + RADIUS;
  result.Top := ScreenPoint.Y - RADIUS;
  result.Bottom := ScreenPoint.Y + RADIUS;
end;

procedure TForm5.FormPaint(Sender: TObject);
begin

  // Draw ball A
  Canvas.Brush.Color := clSkyBlue;
  Canvas.Ellipse(EllipseRectFromPoint(FPosA));

  // Draw ball B
  Canvas.Brush.Color := clMoneyGreen;
  Canvas.Ellipse(EllipseRectFromPoint(FPosB));

end;

procedure TForm5.Timer1Timer(Sender: TObject);
begin
  FPosA.X := FPosA.X + V.X;
  FPosA.Y := FPosA.Y + V.Y;
  Invalidate;

  if Hypot(FPosA.X - FPosB.X, FPosA.Y - FPosB.Y) < 0.1 then
  begin
    Timer1.Enabled := false;
    ShowMessage('We''re there!');
  end;
end;

end.

Two balls:

unit Unit5;

interface

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

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

  TForm5 = class(TForm)
    Timer1: TTimer;
    procedure FormPaint(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
    AreWeThereYetA, AreWeThereYetB: boolean;
    FPosA, FPosB, FPosC: TVector;
    vA, vB: TVector;
  public
    { Public declarations }
  end;

var
  Form5: TForm5;

implementation

uses Math;

{$R *.dfm}

const RADIUS = 16;

function RealPoint(X, Y: real): TVector;
begin
  result.X := X;
  result.Y := Y;
end;

function RoundPoint(P: TVector): TPoint;
begin
  result.X := round(P.X);
  result.Y := round(P.Y);
end;

procedure TForm5.FormCreate(Sender: TObject);
var
  DX, DY: real;
begin
  FPosA := RealPoint(32, 32);
  FPosB := RealPoint(132, 32);
  FPosC := RealPoint(500, 200);

  DX := FPosC.X - FPosA.X;
  DY := FPosC.Y - FPosA.Y;
  vA.X := DX / 100;
  vA.Y := DY / 100;

  DX := FPosC.X - FPosB.X;
  DY := FPosC.Y - FPosB.Y;
  vB.X := DX / 200;
  vB.Y := DY / 200;

end;

function EllipseRectFromPoint(P: TVector): TRect;
var
  ScreenPoint: TPoint;
begin
  ScreenPoint := RoundPoint(P);
  result.Left := ScreenPoint.X - RADIUS;
  result.Right := ScreenPoint.X + RADIUS;
  result.Top := ScreenPoint.Y - RADIUS;
  result.Bottom := ScreenPoint.Y + RADIUS;
end;

procedure TForm5.FormPaint(Sender: TObject);
begin

  // Draw ball A
  Canvas.Brush.Color := clSkyBlue;
  Canvas.Ellipse(EllipseRectFromPoint(FPosA));

  // Draw ball B
  Canvas.Brush.Color := clMoneyGreen;
  Canvas.Ellipse(EllipseRectFromPoint(FPosB));

  // Draw ball C
  Canvas.Brush.Color := clRed;
  Canvas.Ellipse(EllipseRectFromPoint(FPosC));

end;

procedure TForm5.Timer1Timer(Sender: TObject);
begin

  if not AreWeThereYetA then
  begin
    FPosA.X := FPosA.X + VA.X;
    FPosA.Y := FPosA.Y + VA.Y;
  end;

  if not AreWeThereYetB then
  begin
    FPosB.X := FPosB.X + VB.X;
    FPosB.Y := FPosB.Y + VB.Y;
  end;

  Invalidate;

  if Hypot(FPosA.X - FPosC.X, FPosA.Y - FPosC.Y) < 0.1 then
    AreWeThereYetA := true;

  if Hypot(FPosB.X - FPosC.X, FPosB.Y - FPosC.Y) < 0.1 then
    AreWeThereYetB := true;

  if AreWeThereYetA and AreWeThereYetB then
  begin
    Timer1.Enabled := false;
    ShowMessage('We are there!');
  end;
end;

end.

Using arrays and records, it would be easily to generalise to N balls with custom properties (colours, radii, etc.), even random ones. It would also be very easy to implement bouncing. In addition, a real vector type would be good here.