ol中闪烁点动画的实现

概述

本文讲述如何在ol中实现闪烁点动画。

实现效果

实现思路

实现如图的动画，可以用两种思路：
1.overlay+css3动画实现；
2.canvas动画实现。

实现

1、overlay+css3实现

css的实现如下：

@keyframes animate {
  0% { transform: scale(0.3); }
  100% { transform: scale(1); }
}

.animate-overlay {
	width: 30px; 
	height: 30px;
	background: radial-gradient(circle, red, rgba(255, 0, 0, 0));
	border: 1px solid red;
	border-radius: 50%;
	animation: 1s animate infinite;
}

for(var i = 0;i<data.length;i++) {
  var d = data[i];
  var coord = ol.proj.fromLonLat([d.lon, d.lat]);
  var element = document.createElement('div');
  element.classList.add('animate-overlay');
  var overlay = new ol.Overlay({
	  element: element,
  })
  map.addOverlay(overlay);
  overlay.setPosition(coord);
}

2、canvas动画实现

var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
var gradCircle = new GradCircle(ctx);
var radius = 15,
  changeRadius = 0.5;

var imageLayer = new ol.layer.Image({
  source: null,
  zIndex: 2
});
map.addLayer(imageLayer);
var source = new ol.source.ImageCanvas({
  canvasFunction: canvasFunction
});
imageLayer.setSource(source);
var playFlag = null;


window.requestAnimationFrame =(
  window.webkitRequestAnimationFrame||
  window.mozRequestAnimationFrame||
  window.oRequestAnimationFrame||
  window.msRequestAnimationFrame||
  function(callback){
    return window.setTimeout(callback,1000/60);
  }
);

function refresh() {
  playFlag = window.requestAnimationFrame(refresh);
  source.refresh();
}

map.on('movestart', function () {
  window.cancelAnimationFrame(playFlag);
});
map.on('moveend', function () {
  resetState();
});

function canvasFunction(extent, res, pixelRatio, size) {
  canvas.setAttribute('width', size[0]);
  canvas.setAttribute('height', size[1]);
  ctx.clearRect(0, 0 , size[0], size[1]);
  var mapExtent = map.getView().calculateExtent();
  var mapTopLeft = [mapExtent[0], mapExtent[3]];
  var topLeft = [extent[0], extent[3]];
  var tlSrc = map.getPixelFromCoordinate(topLeft);
  var tlMapSrc = map.getPixelFromCoordinate(mapTopLeft);
  var xOff = tlMapSrc[0] - tlSrc[0],
    yOff = tlMapSrc[1] - tlSrc[1];
  //浏览器存在多方的状态下
  ctx.scale(pixelRatio, pixelRatio);
  for(var i = 0;i<data.length;i++) {
    var d = data[i];
    var lonlat = [d.lon, d.lat];
    var coord = ol.proj.fromLonLat(lonlat);
    if(ol.extent.containsCoordinate(mapExtent, coord)) {
      var pixel = map.getPixelFromCoordinate(coord);
      var x = pixel[0] + xOff,
        y = pixel[1] + yOff;
      d.radius = d.radius + changeRadius;
      if(d.radius > radius * 2) d.radius = radius;
      gradCircle.drawGradCircle(x, y, d.radius);
    }
  }
  return canvas;
}
resetState();
function resetState(){
  for(var i = 0;i<data.length;i++) {
    var d = data[i];
    d.radius = radius;
  }
  refresh();
}

---

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