Just press the right or left key to move the rotative object through the screen and space to fire up to 10 new dots over the screen. Firing more than 10 dots will produce an error.

Demo

View the demo

The javascript code

Place the following code in the header of an HTML file.

dx = 0.03;
alpha = Math.PI;
passo = 1.0;
xpos=100;
warray0 = new Array(0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0);
warray1 = new Array(0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0);
warray2 = new Array(0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0);
warray3 = new Array(1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0);
warray4 = new Array(-1.0,-1.0,-1.0,-1.0,-1.0,-1.0,-1.0,-1.0,-1.0,-1.0);

function Tempo()
{
  setTimeout("Accao();",1);
}
function Accao()
{
  alpha = alpha + dx; 
  if ((alpha > 2*Math.PI) | (alpha < Math.PI))
  {
     dx = -dx; 	
  }
	var val = parseInt(Math.sin(alpha) * 60 + 170);
  document.getElementById('ponto_movel').style.top = val.toString()+'px';
  var val = parseInt(Math.cos(alpha) * 60 + xpos);
  document.getElementById('ponto_movel').style.left = val.toString()+'px';
  var val = parseInt(Math.sin(alpha) * 30 + 170);
  document.getElementById('ponto_movel1').style.top = val.toString()+'px';
  var val = parseInt(Math.cos(alpha) * 30 + xpos);
  document.getElementById('ponto_movel1').style.left = val.toString()+'px';
  
  document.getElementById('ponto_fixo').style.left = xpos+'px';

for (i=0; i<10;i++)
  { 
     if (document.getElementById("ponto_bola"+i.toString()).style.visibility == 'visible')
     	document.getElementById("ponto_bola"+i.toString()).style.left = xpos+'px';
  }
  send_ball();	
  Tempo();
}
function send_ball()
{
  for (i=0;i<warray0.length;i++)
   {
      if (parseFloat(warray1[i]) > 0.0 && parseFloat(warray1[i]) <= 300.0 && parseFloat(warray0[i]) > 0.0 && parseFloat(warray0[i]) <= 300.0)
      {
         document.getElementById("ponto_bola"+i.toString()).style.visibility = 'visible'; 
 			 warray0[i] = parseFloat(warray0[i]) + (passo * parseFloat(warray3[i]) * Math.cos(warray2[i]));

document.getElementById("ponto_bola"+i.toString()).style.left = warray0[i]+'px';	
 			 warray1[i] = parseFloat(warray1[i]) + (passo * parseFloat(warray4[i]) * Math.sin(warray2[i]));
         document.getElementById("ponto_bola"+i.toString()).style.top = warray1[i]+'px';	
      }
      else
      {
         warray0[i] = 0.0;
 	  		warray1[i] = 0.0;
         warray3[i] = 1.0;
	  		warray4[i] = -1.0;
	  		document.getElementById("ponto_bola"+i.toString()).style.visibility = 'hidden';  
      }

if (parseFloat(warray0[i]) <= (1.0 + passo) || parseFloat(warray0[i]) >= (299.0 - passo))	
      	warray3[i] = -warray3[i];

if (parseFloat(warray1[i]) <= (1.0 + passo) || parseFloat(warray1[i]) >= (299.0 - passo))	
	  		warray4[i] = -warray4[i];  
	 } 
}

function getInput(evt) 
{
	evt = (evt) ? evt : window.event;
	var charCode = (evt.which) ? evt.which : evt.keyCode;

switch(charCode) {
    case 27:
         //Escape
         break;
    case 32:
         //Espa�o

windice = warray0.length;

for (i=0; i < warray0.length;i++)
			 {
				 if (warray0[i] == 0)
					windice = i;
			 }

warray0[windice] = document.getElementById('ponto_fixo').style.left;
         warray1[windice] = document.getElementById('ponto_fixo').style.top;
         warray2[windice] = alpha;

break;
    case 37:
         //Esquerda         
         xpos=xpos-5;
         break;
    case 38:
         //Cima
         break;
    case 39:
         //Direita
	 xpos = xpos+5;
         break;
    case 40:
         //Baixo
         break;
  }

}
</Script>

The HMTL code

This would be the body of the HTML file.

History

2008-07-01: First version

Last Updated on

About David Domingues: David Domingues is a professional IT analyst. Visit http://www.webrickco.com.

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The sample object