ObjectMovingBalls

Introduction

George was trying object-oriented code for the first time when he created this interesting visual effect. The title refers to moving balls, but in the absence of background refreshes the "balls" soon adopt different shapes. See also the use of much of the code in the form-based Compendium.

The code follows the graphic in action.

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The Code

unit ObjectMovingBalls;
{
    Copyright (c) 2014 George Wright

    Licensed under the Apache License, Version 2.0 (the "License"); you may not
    use this file except in compliance with the License, as described at
    http://www.apache.org/licenses/ and http://www.pp4s.co.uk/licenses/
}
interface

uses 
  W3System, W3Components, W3Application, W3Game, W3GameApp, W3Graphics;
type
  TBall = class(TObject)
  private
     x, y, width, height : float;
     colour : string;
     Speed : integer;
  public
    constructor create(newX, newY, newHeight, newWidth: float; newColour: string; newSpeed : integer);
    procedure move;
  end;

  TApplication = class(TW3CustomGameApplication)
  private
    i : integer;
  protected
    procedure  ApplicationStarting; override;
    procedure  ApplicationClosing; override;
    procedure  PaintView(Canvas: TW3Canvas); override;
  end;

const
  DELAY = 50;
var
  Ball : array [0..6] of  TBall;
  Timer : integer;

implementation

constructor TBall.create(newX, newY, newHeight, newWidth : float; newColour : string; newSpeed : integer);
begin
  x := newX;
  y := newY;
  height := newHeight;
  width := newWidth;
  colour := newColour;
  speed := newSpeed;
end;

procedure TBall.move;
begin
  if (x < 300 - width) and (y <= 0) then
    x += speed;

  if (x >= 300 - width) and (y < 300 - height) then
    y += speed;

  if (x > 0) and (y >= 300 - height) then
    x -= speed;

  if (y > 0) and (x <= 0) then
    y -= speed;

  if x > 300 - width then
    x := 300 - width;
  if x < 0 then
    x := 0;
  if y < 0 then
    y := 0;
  if y > 300 - height then
    y := 300 - height;
end;

procedure TApplication.ApplicationStarting;
begin
  inherited;
  GameView.Delay := 20;
  Timer := 0;
                         //newX, newY, newHeight, newWidth, newColour, newSpeed
  Ball[0] := TBall.create(- DELAY, 0, DELAY - 10, DELAY - 10, 'red', 1);
  Ball[1] := TBall.create(- DELAY * 2, 0, DELAY - 10, DELAY - 10, 'orange', 2);
  Ball[2] := TBall.create(- DELAY * 3, 0, DELAY - 10, DELAY - 10, 'yellow', 3);
  Ball[3] := TBall.create(- DELAY * 4, 0, DELAY - 10, DELAY - 10, 'green', 4);
  Ball[4] := TBall.create(- DELAY * 5, 0, DELAY - 10, DELAY - 10, 'blue', 5);
  Ball[5] := TBall.create(- DELAY * 6, 0, DELAY - 10, DELAY - 10, 'purple', 6);
  Ball[6] := TBall.create(- DELAY * 7, 0, DELAY - 10, DELAY - 10, 'rgb(153, 50, 204)', 7);
  GameView.StartSession(True);
end;

procedure TApplication.ApplicationClosing;
begin
  GameView.EndSession;
  inherited;
end;

procedure TApplication.PaintView(Canvas: TW3Canvas);
begin
  if Timer = 0 then
    begin
      // Clear background
      Canvas.FillStyle := 'white';
      Canvas.FillRectF(0, 0, GameView.Width, GameView.Height);
    end;
  while i <= 6 do
    begin
      Canvas.FillStyle := (Ball[i].colour);
      Canvas.BeginPath;
      Canvas.Ellipse(Ball[i].x, Ball[i].y, Ball[i].x + Ball[i].width, Ball[i].y + Ball[i].height);
      Canvas.ClosePath;
      Canvas.Fill;
      Ball[i].move;
      inc(i);
    end;
  i := 0;
  Timer += 1;
end;

end.