# Animate from x0y0 to x1y1

suggest change

Use vectors to calculate incremental [x,y] from [startX,startY] to [endX,endY]

``````// dx is the total distance to move in the X direction
var dx = endX - startX;

// dy is the total distance to move in the Y direction
var dy = endY - startY;

// use a pct (percentage) to travel the total distances
// start at 0% which == the starting point
// end at 100% which == then ending point
var pct=0;

// use dx & dy to calculate where the current [x,y] is at a given pct
var x = startX + dx * pct/100;
var y = startY + dx * pct/100;``````

Example Code:

``````// canvas vars
var canvas=document.createElement("canvas");
document.body.appendChild(canvas);
canvas.style.border='1px solid red';
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
// canvas styles
ctx.strokeStyle='skyblue';
ctx.fillStyle='blue';

// animating vars
var pct=101;
var startX=20;
var startY=50;
var endX=225;
var endY=100;
var dx=endX-startX;
var dy=endY-startY;

// start animation loop running
requestAnimationFrame(animate);

// listen for mouse events
window.onmousedown=(function(e){handleMouseDown(e);});
window.onmouseup=(function(e){handleMouseUp(e);});

// constantly running loop
// will animate dot from startX,startY to endX,endY
function animate(time){
// demo: rerun animation
if(++pct>100){pct=0;}
// update
x=startX+dx*pct/100;
y=startY+dy*pct/100;
// draw
ctx.clearRect(0,0,cw,ch);
ctx.beginPath();
ctx.moveTo(startX,startY);
ctx.lineTo(endX,endY);
ctx.stroke();
ctx.beginPath();
ctx.arc(x,y,5,0,Math.PI*2);
ctx.fill()
// request another animation loop
requestAnimationFrame(animate);
}``````