canvas虚线绘制

function drawDashLine(start, end, dash) {
    var deltX = end[0] - start[0];
    var deltY = end[1] - start[1];
    var totalDis = Math.sqrt(deltX * deltX + deltY * deltY);

    var getPos = function (pos, dis) {
        var deltXS = pos[0] - start[0];
        var deltYS = pos[1] - start[1];
        var baseDis = Math.sqrt(deltXS * deltXS + deltYS * deltYS);
        var percent = (dis + baseDis) / totalDis;
        var x = start[0] + deltX * percent;
        var y = start[1] + deltY * percent;
        return [x, y];
    };

    var dis = 0;
    for(var i = 0; i < dash.length; i++) {
        dis += dash[i];
    }
    var count = Math.ceil(totalDis / dis);
    var _start = start.concat([]);
    ctx.lineWidth = 3;
    ctx.strokeStyle = 'red';
    ctx.lineCap = 'round';
    ctx.lineJoin = 'round';
    for (var i = 0; i < count; i++) {
        for(var j = 0; j < dash.length; j++) {
            if(j % 2===0) {
                ctx.beginPath();
                ctx.moveTo(_start[0], _start[1]);
                _start = getPos(_start, dash[j]);
                ctx.lineTo(_start[0], _start[1]);
                ctx.stroke();
            } else {
                _start = getPos(_start, dash[j]);
            }
        }
    }
}
// 调用绘制
drawDashLine([10, 10], [500, 500], [15, 10, 1, 10]);