Creating 2-D Animations on Canvas - interactive spring

In this tutorial, you will learn the following:

  • How to create a spring using Math.sin() function of JavaScript.
  • How to create a pendulum bob using radial gradient.
  • How to oscillate the ball on the spring vertically.
  • How to choose a speed from a choice of three.
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Interactive Oscillating Spring

The spring is produced by manipulating Math.sin method of Math object.

The sphere is produced by context.arc method; the radial gradient produces the spherical appearance of the circle.

The speed is controlled by giving three different time intervals to window.setInterval() method.

Please choose the speed, and then click the Run button.

Slow



Medium



Fast

 

Please stop the spring before changing the speed.

 

The source code for the animation is given below:

<!--hidden element to store the values for animation--------------->
<input type="hidden" id="h" value="0" />
<canvas id="Canvas_Two" width="400" height="300" style="border:2px solid red;" class="imgforcontent">
</canvas>
<!----radio buttons for speed control---------------------------->
<form name="spring" action="">
<input id="R4" name="speed" value="Slow" type="radio" />Slow<br /><br />
<input id="R5" name="speed" value="Medium" type="radio" />Medium<br /><br />
<input id="R6" name="speed" value="Fast" type="radio" />Fast<br /><br />
</form>
<!---------------buttons to start and stop the animation------------------------>
<div style="width:400px;">
<input type="button" style="float:left;margin-left:10px;" value="Run" onclick="anim1()" id="Animation" />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<input type="button" style="float:right;margin-right:10px;" value="Stop" onclick="window.clearInterval(xx)" id="Stopping" >
</div>
<canvas id="Canvas_Two" width="400" height="300" style="border:5px solid red"></canvas> <script> var canvas = document.getElementById('Canvas_Two');
var context1 = canvas.getContext('2d');
//code for static spring in grey colour
context1.beginPath();
context1.moveTo(200,0);
for(var i=0;i<=220;i++)
{
context1.lineTo(200 +20*Math.sin(5*i*Math.PI/180),i*0.5);
context1.lineWidth=5;
context1.strokeStyle='grey';
context1.stroke();
}
// code for the ball in blue colour
context1.beginPath();
context1.arc(200,100,35,0,2*Math.PI,false);
var grd = context1.createRadialGradient(200, 100, 5, 200, 100, 30);
// light blue
grd.addColorStop(0, '#8ED6FF');
// dark blue
grd.addColorStop(1, '#004CB3');
context1.fillStyle=grd;
context1.fill();
var a=1;
//code for the motion of the spring and the ball
function move(){
var x=eval(document.getElementById('h').value);
x=x+a
if (x==8){a=-1;}
if (x==4){a=1;}
context1.clearRect(0,0,400,300);
context1.beginPath();
context1.moveTo(200,0);
for(var i=0;i<=220;i++)
{
context1.lineTo(200 +20*Math.sin(5*i*Math.PI/180),i*x*0.1);
context1.lineWidth=5;
context1.strokeStyle='grey';
context1.stroke();
}
context1.beginPath();
context1.arc(200,x*20+40,35,0,2*Math.PI,false);
var grd = context1.createRadialGradient(200, x*20+40, 5, 200, x*20+40, 30);
// light blue
grd.addColorStop(0, '#8ED6FF');
// dark blue
grd.addColorStop(1, '#004CB3');
context1.fillStyle=grd;
context1.fill();
document.getElementById('h').value=x;
}
// code for timing
function anim1() {
if
(document.getElementById('R4').checked)
{ sp = 400; }
else if (document.getElementById('R5').checked) { sp = 300; }
else if (document.getElementById('R6').checked) { sp = 200; }
else
{ sp = 500; }
xx = window.setInterval('move()', sp);
}
// code for stopping
function stop1() {
//empty the hidden element on exit
document.getElementById('h2').value = 4;
window.clearInterval(xx);
}
</script>

 

All Canvas Animations

 

 

 

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