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@wjx wjx/mouse-trail.html
Created Nov 30, 2016

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Implementing mouse trail using requestAnimationFrame for EloquentJavaScript Exercise 14.2
<!doctype html>
<style>
.trail { /* className for the trail elements */
position: absolute;
height: 6px; width: 6px;
border-radius: 3px;
background: teal;
}
body {
height: 300px;
}
</style>
<body>
<script>
var pointerX, pointerY;
var lastX = null, lastY = null;
var dots = [];
for (var i = 0; i < 12; i++) {
var node = document.createElement("div");
node.className = "trail";
node.setAttribute("targetTime", i + 1);
document.body.appendChild(node);
dots.push(node);
}
var currentDot = 0;
addEventListener("mousemove", function(event) {
pointerX = event.pageX;
pointerY = event.pageY;
});
var delta = 0, lastTime = null;
function animate(time) {
if (lastTime != null)
delta = time - lastTime;
lastTime = time;
dots.forEach(function(dot) {
var boundingObj = dot.getBoundingClientRect();
var currentX = boundingObj.left + 3;
var currentY = boundingObj.top + 3;
if (Math.abs(currentX - pointerX) < 1 && Math.abs(currentY - pointerY) < 1) {
dot.style.left = pointerX - 3;
dot.style.top = pointerY - 3;
return;
}
var currentDistance = Math.sqrt((currentX - pointerX) * (currentX - pointerX) +
(currentY - pointerY) * (currentY - pointerY));
if (pointerX != lastX || pointerY != lastY) {
//targetTime is in second
var v = currentDistance / (dot.getAttribute("targetTime") * 1000);
dot.setAttribute("velocity", v);
}
var step = dot.getAttribute("velocity") * delta;
//step * cos
var stepX = step * ((pointerX - currentX) / currentDistance);
dot.style.left = boundingObj.left + stepX + "px";
//step * sin
var stepY = step * ((pointerY - currentY) / currentDistance);
dot.style.top = boundingObj.top + stepY + "px";
});
lastX = pointerX;
lastY = pointerY;
requestAnimationFrame(animate);
}
requestAnimationFrame(animate);
</script>
</body>
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