我能想到两种方法来完成这个任务。一种是在画出第一个点后暂停一段时间,再画出另一个点。这就是我提供的第一个示例。第二种方法涉及将部分线条绘制到当前目标位置,这样会使绘图效果更加平滑。顺便说一下,在这两个示例中我都使用了requestAnimationFrame
,它是推荐用于任何类型的canvas动画的方式。
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d");
canvas.width = 400;
canvas.height = 200;
var points = [],
currentPoint = 1,
nextTime = new Date().getTime()+500,
pace = 200;
for (var i = 0; i < 50; i++) {
points.push({
x: i * (canvas.width/50),
y: 100+Math.sin(i) * 10
});
}
function draw() {
if(new Date().getTime() > nextTime){
nextTime = new Date().getTime() + pace;
currentPoint++;
if(currentPoint > points.length){
currentPoint = 0;
}
}
ctx.clearRect(0,0,canvas.width, canvas.height);
ctx.beginPath();
ctx.moveTo(points[0].x, points[0].y);
ctx.lineWidth = 2;
ctx.strokeStyle = '#2068A8';
ctx.fillStyle = '#2068A8';
for (var p = 1, plen = currentPoint; p < plen; p++) {
ctx.lineTo(points[p].x, points[p].y);
}
ctx.stroke();
requestAnimFrame(draw);
}
draw();
演示实例
如果您发现画出的线条有些粗糙,您可以按照以下步骤使其更加平滑。
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d");
canvas.width = 400;
canvas.height = 200;
var points = [],
currentPoint = 1,
speed = 2,
targetX = 0,
targetY = 0,
x = 0,
y = 0;
for (var i = 0; i < 50; i++) {
points.push({
x: i * (canvas.width/50),
y: 100+Math.sin(i) * 10
});
}
targetX = points[1].x;
targetY = points[1].y;
x = points[0].x;
y = points[0].y;
function draw() {
var tx = targetX - x,
ty = targetY - y,
dist = Math.sqrt(tx*tx+ty*ty),
velX = (tx/dist)*speed,
velY = (ty/dist)*speed;
x += velX
y += velY;
if(dist < 1){
currentPoint++;
if(currentPoint >= points.length){
currentPoint = 1;
x = points[0].x;
y = points[0].y;
}
targetX = points[currentPoint].x;
targetY = points[currentPoint].y;
}
ctx.clearRect(0,0,canvas.width, canvas.height);
ctx.beginPath();
ctx.moveTo(points[0].x, points[0].y);
ctx.lineWidth = 2;
ctx.strokeStyle = '#2068A8';
ctx.fillStyle = '#2068A8';
for (var p = 0, plen = currentPoint-1; p < plen; p++) {
ctx.lineTo(points[p].x, points[p].y);
}
ctx.lineTo(x, y);
ctx.stroke();
requestAnimFrame(draw);
}
draw();
实时演示