Qt Reference Documentation

# pong.js Example File

script/context2d/scripts/pong.js

     // globals
     playarea_canvas = document.getElementById('tutorial');
     playarea_canvas.resize(320,200);
     playarea = playarea_canvas.getContext('2d');
     //p1_scr = document.getElementById('p1_scr');
     //p2_scr = document.getElementById('p2_scr');
     //status_msg = document.getElementById('status');
     //debug = document.getElementById('debug');
     ball_direction = 0;
     up = -1;
     down = 1;

     //key codes
     key_up = 38;
     key_down = 40;
     key_W = 87;
     key_S = 83;
     key_pause = 32;

     speed = 2;                      //controls the speed of the ball
     paddle_inc = 10;        //how many pixels paddle can move in either direction
     pause = false;

     player_1 = 0;           //player IDs
     player_2 = 1;
     player_1_scr = 0;       //player scores
     player_2_scr = 0;
     player_1_direction = null;      //null = no movement whatsoever
     player_2_direction = null;

     pa = new Array();
     divider = new Array();
     paddle_1 = new Array();
     paddle_2 = new Array();
     ball = new Array();

     function sleep(numberMillis)
     {
         var now = new Date();
         var exitTime = now.getTime() + numberMillis;
         while (true) {
             now = new Date();
             if (now.getTime() > exitTime)
                 return;
         }
     }

     function init()
     {
         pa['width'] = 150;
         pa['height'] = 140;
         pa['player_margin'] = 10;           //area behind player paddles
         pa['foreground'] = "#FFFFFF";
         pa['background'] = "#000000";

         divider['pos'] = pa['width']/2;
         divider['width'] = 4;

         paddle_1['width'] = 8;
         paddle_1['height'] = 64;
         paddle_1['x'] = pa['player_margin'];
         paddle_1['y'] = (pa['height'] /2 ) - (paddle_1['height'] / 2);

         paddle_2['width'] = 8;
         paddle_2['height'] = 64;
         paddle_2['x'] = (pa['width'] - pa['player_margin'] - paddle_2['width']);
         paddle_2['y'] = (pa['height'] /2 ) - (paddle_2['height'] / 2);

         ball['width'] = 10;
         ball['height'] = 10;
         ball['x'] = (pa['width']/2) - (ball['width'] / 2);
         ball['y'] = (pa['height']/2) - (ball['height'] / 2);

         ball_direction = Math.random() * 360;       //initialize ball direction, which is determined by angle, at random
         speed = 2;
     }

     function renderPlayarea()
     {
         playarea.beginPath();

         playarea.clearRect(0,0,pa['width'],pa['height']);
         playarea.fillStyle = pa['background'];
         playarea.strokeStyle = pa['foreground'];
         playarea.fillRect(0,0, pa['width'], pa['height']);

         //move paddles
         if(player_1_direction != null)
             {
                 if(player_1_direction == up)
                     paddle_1['y'] = paddle_1['y'] - paddle_inc;
                 else
                     paddle_1['y'] = paddle_1['y'] + paddle_inc;
             }
         if(player_2_direction != null)
             {
                 if(player_2_direction == up)
                     paddle_2['y'] = paddle_2['y'] - paddle_inc;
                 else
                     paddle_2['y'] = paddle_2['y'] + paddle_inc;
             }
         playarea.rect(paddle_1['x'],paddle_1['y'],paddle_1['width'],paddle_1['height']);
         playarea.rect(paddle_2['x'],paddle_2['y'],paddle_2['width'],paddle_2['height']);

         //move ball
         playarea.rect(ball['x'], ball['y'], ball['width'], ball['height']);
         ball['x'] = ball['x'] + Math.cos((ball_direction)*Math.PI/180) * speed;
         ball['y'] = ball['y'] + Math.sin((ball_direction)*Math.PI/180) * speed;

         playarea.fillStyle = pa['foreground'];
         playarea.fill();

         playarea.beginPath();
         //redraw divider
         playarea.lineWidth = divider['width'];
         playarea.lineTo(divider['pos'], 0);
         playarea.lineTo(divider['pos'], pa['height'] = 200);
         playarea.lineWidth = 1;

         playarea.stroke();
         playarea.closePath();
     }

     function testCollisions()
     {
         //make sure paddles don't go beyond play area
         if(((paddle_1['y'] <= 0) && (player_1_direction == up)) || ((paddle_1['y'] >= (pa['height'] - paddle_1['height'])) && (player_1_direction == down)))
             player_1_direction = null;
         if(((paddle_2['y'] <= 0) && (player_2_direction == up)) || ((paddle_2['y'] >= (pa['height'] - paddle_2['height'])) && (player_2_direction == down)))
             player_2_direction = null;

         //check to see if ball went beyond paddles, and if so, score accordingly and reset playarea
         if(ball['x'] <= 0)
             {
                 setScore(player_2);
                 init()
                     sleep(1000);
             }
         if(ball['x'] >= (pa['width'] - ball['width']))
             {
                 setScore(player_1);
                 init();
                 sleep(1000);
             }

         //check to see if ball hit top or bottom wall. if so, change direction
         if((ball['y'] >= (pa['height'] - ball['height'])) || ball['y'] <= 0)
             ball_direction = -ball_direction;

         //check to see if the ball hit a paddle, and if so, change ball angle dependant on where it hit the paddle
         if((ball['x'] <= (paddle_1['x'] + paddle_1['width'])) && (ball['y'] >= paddle_1['y']) && (ball['y'] <= (paddle_1['y'] + paddle_1['height'])))
             {
                 ball_direction = -ball_direction/2;
                 speed += .5;
             }
         if(((ball['x'] + ball['width']) >= paddle_2['x']) && (ball['y'] >= paddle_2['y']) && (ball['y'] <= (paddle_2['y'] + paddle_2['height'])))
             {
                 ball_direction = (180+ball_direction)/2;
                 speed += .5;
             }
     }

     function setScore(p)
     {
         if(p == player_1)
             {
                 player_1_scr++;
                 //p1_scr.firstChild.nodeValue = player_1_scr;
             }
         if(p == player_2)
             {
                 player_2_scr++;
                 //p2_scr.firstChild.nodeValue = player_2_scr;
             }
     }

     //handle input
     document.onkeydown = function(ev)
     {
         switch(ev.keyCode)
         {
             case key_W:
             player_1_direction = up;
             break;
             case key_S:
             player_1_direction = down;
             break;
             case key_up:
             player_2_direction = up;
             break;
             case key_down:
             player_2_direction = down;
             break;
         }
     }

     document.onkeyup = function(ev)
     {
         switch(ev.keyCode)
         {
             case key_W:
             case key_S:
             player_1_direction = null;
             break;
             case key_up:
             case key_down:
             player_2_direction = null;
             break;
             case key_pause:
             if(pause == false)
             {
                 clearInterval(game);
                 //status_msg.style.visibility = "visible";
                 pause = true;
             }
             else
             {
                 game = setInterval(main, 25);
                 //status_msg.style.visibility = "hidden";
                 pause = false;
             }
             break;
         }
     }

     function main()
     {
         testCollisions();
         renderPlayarea();
     }

     init();
     game = setInterval(main, 25);