先随便试验了一下效果,发现clearRect没有清除画布?什么情况?

var canvas = wx.createCanvas();

var ctx = canvas.getContext(‘2d’);

var ballX = 200;

function drawBall(ballX) {

ctx.clearRect(0, 0, canvas.width, canvas.height);

ctx.fillStyle = “#fff”;

ctx.arc(ballX, 500, 10, 0, 2 * Math.PI);

ctx.fill();

}

setInterval(function () {

ctx.clearRect(0, 0, canvas.width, canvas.height);

ballX-=10;

drawBall(ballX);

}, 500);