I want to do animation of an object along a particular path

Question

I have to move the small rectangle on the path. The rectangle moves after a click inside the canvas.

I am not able to animate it as the object just jumps to the required point.

Please find the code on Fiddle.

HTML

<canvas id="myCanvas" width=578 height=200></canvas>

CSS

#myCanvas {
    width:578px;
    height:200px;
    border:2px thin;
}

JavaScript

var myRectangle = {
    x: 100,
    y: 20,
    width: 25,
    height: 10,
    borderWidth: 1
};

$(document).ready(function () {
    $('#myCanvas').css("border", "2px solid black");
    var canvas = document.getElementById('myCanvas');
    var context = canvas.getContext('2d');
    var cntxt = canvas.getContext('2d');
    drawPath(context);
    drawRect(myRectangle, cntxt);

    $('#myCanvas').click(function () {
        function animate(myRectangle, canvas, cntxt, startTime) {
            var time = (new Date()).getTime() - startTime;
            var linearSpeed = 10;
            var newX = Math.round(Math.sqrt((100 * 100) + (160 * 160)));
            if (newX < canvas.width - myRectangle.width - myRectangle.borderWidth / 2) {

                myRectangle.x = newX;

            }


            context.clearRect(0, 0, canvas.width, canvas.height);
            drawPath(context);
            drawRect(myRectangle, cntxt);

            // request new frame
            requestAnimFrame(function () {
                animate(myRectangle, canvas, cntxt, startTime);
            });
        }
        drawRect(myRectangle, cntxt);
        myRectangle.x = 100;
        myRectangle.y = 121;
        setTimeout(function () {
            var startTime = (new Date()).getTime();
            animate(myRectangle, canvas, cntxt, startTime);
        }, 1000);

    });
});

$(document).keypress(function (e) {
    if (e.which == 13) {


        $('#myCanvas').click();

    }
});

function drawRect(myRectangle, cntxt) {

    cntxt.beginPath();
    cntxt.rect(myRectangle.x, myRectangle.y, myRectangle.width, myRectangle.height);
    cntxt.fillStyle = 'cyan';
    cntxt.fill();

    cntxt.strokeStyle = 'black';
    cntxt.stroke();
};

function drawPath(context) {

    context.beginPath();
    context.moveTo(100, 20);

    // line 1
    context.lineTo(200, 160);
    // quadratic curve
    context.quadraticCurveTo(230, 200, 250, 120);

    // bezier curve
    context.bezierCurveTo(290, -40, 300, 200, 400, 150);

    // line 2
    context.lineTo(500, 90);
    context.lineWidth = 5;
    context.strokeStyle = 'blue';
    context.stroke();
};

Answer 1

Here is how to move an object along a particular path

Animation involves movement over time. So for each “frame” of your animation you need to know the XY coordinate where to draw your moving object (rectangle).

This code takes in a percent-complete (0.00 to 1.00) and returns the XY coordinate which is that percentage along the path segment. For example:

• 0.00 will return the XY at the beginning of the line (or curve).
• 0.50 will return the XY at the middle of the line (or curve).
• 1.00 will return the XY at the end of the line (or curve).

Here is the code to get the XY at the specified percentage along a line:

// line: percent is 0-1
function getLineXYatPercent(startPt,endPt,percent) {
    var dx = endPt.x-startPt.x;
    var dy = endPt.y-startPt.y;
    var X = startPt.x + dx*percent;
    var Y = startPt.y + dy*percent;
    return( {x:X,y:Y} );
}

Here is the code to get the XY at the specified percentage along a quadratic bezier curve:

// quadratic bezier: percent is 0-1
function getQuadraticBezierXYatPercent(startPt,controlPt,endPt,percent) {
    var x = Math.pow(1-percent,2) * startPt.x + 2 * (1-percent) * percent * controlPt.x + Math.pow(percent,2) * endPt.x; 
    var y = Math.pow(1-percent,2) * startPt.y + 2 * (1-percent) * percent * controlPt.y + Math.pow(percent,2) * endPt.y; 
    return( {x:x,y:y} );
}

Here is the code to get the XY at the specified percentage along a cubic bezier curve:

// cubic bezier percent is 0-1
function getCubicBezierXYatPercent(startPt,controlPt1,controlPt2,endPt,percent){
    var x=CubicN(percent,startPt.x,controlPt1.x,controlPt2.x,endPt.x);
    var y=CubicN(percent,startPt.y,controlPt1.y,controlPt2.y,endPt.y);
    return({x:x,y:y});
}

// cubic helper formula at percent distance
function CubicN(pct, a,b,c,d) {
    var t2 = pct * pct;
    var t3 = t2 * pct;
    return a + (-a * 3 + pct * (3 * a - a * pct)) * pct
    + (3 * b + pct * (-6 * b + b * 3 * pct)) * pct
    + (c * 3 - c * 3 * pct) * t2
    + d * t3;
}

And here is how you put it all together to animate the various segments of your path

// calculate the XY where the tracking will be drawn

if(pathPercent<25){
    var line1percent=pathPercent/24;
    xy=getLineXYatPercent({x:100,y:20},{x:200,y:160},line1percent);
}
else if(pathPercent<50){
    var quadPercent=(pathPercent-25)/24
    xy=getQuadraticBezierXYatPercent({x:200,y:160},{x:230,y:200},{x:250,y:120},quadPercent);
}
else if(pathPercent<75){
    var cubicPercent=(pathPercent-50)/24
    xy=getCubicBezierXYatPercent({x:250,y:120},{x:290,y:-40},{x:300,y:200},{x:400,y:150},cubicPercent);
}
else {
    var line2percent=(pathPercent-75)/25
    xy=getLineXYatPercent({x:400,y:150},{x:500,y:90},line2percent);
}

// draw the tracking rectangle
drawRect(xy);

Here is working code and a Fiddle: http://jsfiddle.net/m1erickson/LumMX/

<!doctype html>
<html lang="en">
<head>

  <style>
      body{ background-color: ivory; }
      canvas{border:1px solid red;}
  </style>

  <link rel="stylesheet" href="http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css" />
  <script src="http://code.jquery.com/jquery-1.9.1.js"></script>
  <script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>

  <script>

  $(function() {

      var canvas=document.getElementById("canvas");
      var ctx=canvas.getContext("2d");

      // set starting values
      var fps = 60;
      var percent=0
      var direction=1;

      // start the animation
      animate();

      function animate() {

          // set the animation position (0-100)
          percent+=direction;
          if(percent<0){ percent=0; direction=1; };
          if(percent>100){ percent=100; direction=-1; };

          draw(percent);

          // request another frame
          setTimeout(function() {
              requestAnimationFrame(animate);
          }, 1000 / fps);
      }


      // draw the current frame based on sliderValue
      function draw(sliderValue){

          // redraw path
          ctx.clearRect(0,0,canvas.width,canvas.height);
          ctx.lineWidth = 5;

          ctx.beginPath();
          ctx.moveTo(100, 20);
          ctx.lineTo(200, 160);
          ctx.strokeStyle = 'red';
          ctx.stroke();

          ctx.beginPath();
          ctx.moveTo(200, 160);
          ctx.quadraticCurveTo(230, 200, 250, 120);
          ctx.strokeStyle = 'green';
          ctx.stroke();

          ctx.beginPath();
          ctx.moveTo(250,120);
          ctx.bezierCurveTo(290, -40, 300, 200, 400, 150);
          ctx.strokeStyle = 'blue';
          ctx.stroke();

          ctx.beginPath();
          ctx.moveTo(400, 150);
          ctx.lineTo(500, 90);
          ctx.strokeStyle = 'gold';
          ctx.stroke();

          // draw the tracking rectangle
          var xy;

          if(sliderValue<25){
              var percent=sliderValue/24;
              xy=getLineXYatPercent({x:100,y:20},{x:200,y:160},percent);
          }
          else if(sliderValue<50){
              var percent=(sliderValue-25)/24
              xy=getQuadraticBezierXYatPercent({x:200,y:160},{x:230,y:200},{x:250,y:120},percent);
          }
          else if(sliderValue<75){
              var percent=(sliderValue-50)/24
              xy=getCubicBezierXYatPercent({x:250,y:120},{x:290,y:-40},{x:300,y:200},{x:400,y:150},percent);
          }
          else {
              var percent=(sliderValue-75)/25
              xy=getLineXYatPercent({x:400,y:150},{x:500,y:90},percent);
          }
          drawRect(xy,"red");

      }


      // draw tracking rect at xy
      function drawRect(point,color){
          ctx.fillStyle="cyan";
          ctx.strokeStyle="gray";
          ctx.lineWidth=3;
          ctx.beginPath();
          ctx.rect(point.x-13,point.y-8,25,15);
          ctx.fill();
          ctx.stroke();
      }

      // draw tracking dot at xy
      function drawDot(point,color){
          ctx.fillStyle=color;
          ctx.strokeStyle="black";
          ctx.lineWidth=3;
          ctx.beginPath();
          ctx.arc(point.x,point.y,8,0,Math.PI*2,false);
          ctx.closePath();
          ctx.fill();
          ctx.stroke();
      }

      // line: percent is 0-1
      function getLineXYatPercent(startPt,endPt,percent) {
          var dx = endPt.x-startPt.x;
          var dy = endPt.y-startPt.y;
          var X = startPt.x + dx*percent;
          var Y = startPt.y + dy*percent;
          return( {x:X,y:Y} );
      }

      // quadratic bezier: percent is 0-1
      function getQuadraticBezierXYatPercent(startPt,controlPt,endPt,percent) {
          var x = Math.pow(1-percent,2) * startPt.x + 2 * (1-percent) * percent * controlPt.x + Math.pow(percent,2) * endPt.x; 
          var y = Math.pow(1-percent,2) * startPt.y + 2 * (1-percent) * percent * controlPt.y + Math.pow(percent,2) * endPt.y; 
          return( {x:x,y:y} );
      }

      // cubic bezier percent is 0-1
      function getCubicBezierXYatPercent(startPt,controlPt1,controlPt2,endPt,percent){
          var x=CubicN(percent,startPt.x,controlPt1.x,controlPt2.x,endPt.x);
          var y=CubicN(percent,startPt.y,controlPt1.y,controlPt2.y,endPt.y);
          return({x:x,y:y});
      }

      // cubic helper formula at percent distance
      function CubicN(pct, a,b,c,d) {
          var t2 = pct * pct;
          var t3 = t2 * pct;
          return a + (-a * 3 + pct * (3 * a - a * pct)) * pct
          + (3 * b + pct * (-6 * b + b * 3 * pct)) * pct
          + (c * 3 - c * 3 * pct) * t2
          + d * t3;
      }


  });   // end $(function(){});

  </script>
</head>
<body>
    <canvas id="canvas" width=600 height=300></canvas>
</body>
</html>