jquery - Parabolic motion with javascript -


i'm making script simulate parabolic motion of ball. not understand i'm wrong, works jquery. think it's problem in frame.

    <html>      <head>         <script>             var c = document.getelementbyid("mycanvas");             var ctx = c.getcontext("2d");             var x = 100;              function init() {             setinterval("draw()", 1);             }              function draw() {                 ctx.beginpath();                 ctx.arc(x, motopar(x + 2, 0, 100, 100), 30, 0, math.pi * 2);                 ctx.stroke();             }               function motopar(x, x0, vx, vy){                 var y;                 var g = 3;                 y = -1/2 * g * (x * x) / (vx * vx) + vy / vx * x;                 return y;             }         </script> </head>  <body>         <canvas id="mycanvas" width="600" height="600" style="border: 1px solid black;">             browser not support html5 canvas tag.         </canvas> </body>      </html>

i able ball moving, though not parabolically.

1 wrap starter code in window.onload , invoke init() inside of (though keep var declarations c, ctx, , x globals -- ie outside of window.onload function)):

    var c, ctx, x;      window.onload = function() { // <--  invoked when page ready        c = document.getelementbyid("mycanvas"); // c null if dom isn't done        ctx = c.getcontext("2d");        x = 100;        init(); // <-- make sure call :)     }

2 pass identifier draw setinterval (function names variables too)

     setinterval(draw, 1);

3 ball drawn won't moving. far motion, i'll leave you, threw in ++x middle of draw() function @ least gets ball slide bottom right


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