在实时折线图D3.js中的SVG路径的末尾绘制圆圈

Question

我需要在实时折线图中的SVG路径的末尾绘制圆圈。 我使用d3.js绘制图表。 一切都很好，但是这个麻烦使我困惑。

请告诉我代码中的错误，并帮助我找到更好的解决方案。

谢谢！

JS代码：

var GraphIndex = (function() {
        var n = 10,
            duration = 15000,
            now = new Date(Date.now() - duration),
            random = d3.random.normal(0, 100),
            data = d3.range(n).map(random);

        var width = 379,
            height = 138;

        // X axis
        var x = d3.time.scale()
            .domain([now - (n - 2) * duration, now - duration])
            .range([0, width - 40]);

        // Y axis
        var y = d3.scale.linear()
            .domain([(-1)*d3.max(data) - 100, d3.max(data) + 100])
            .range([height, 0]);

        var line = d3.svg.line()
           .interpolate("linear")
           .x(function(d, i) { return x(now - (n - 1 - i) * duration); })
           .y(function(d, i) { return y(d); });

        var svg = d3.select(".graph-holder").append("svg")
           .attr("width", width)
           .attr("height", height + 30);

        svg.append("defs").append("clipPath")
           .attr("id", "clip")
         .append("rect")
           .attr("width", width - 40)
           .attr("height", height);

        // X Axis
        var axis = svg.append("g")
            .attr("class", "x-axis")
            .attr("transform", "translate(0," + height + ")")
            .call(x.axis = d3.svg.axis().scale(x).orient("bottom").ticks(d3.time.minutes, 1));

        // Line
        var path = svg.append("g")
            .attr("clip-path", "url(#clip)")
            .attr("class", "path-area")
          .append("path")
            .data([data])
            .attr("class", "line")
            .attr("id", "myPath");

        //Draw the Circle
        var circle = d3.select(".path-area")
            .append("svg:circle")
                .attr("cx", 335)
                .attr("cy", y(data[n - 2]))
                .attr("r", 4)
                .attr("class", "circle");

        this.tick = (function(){
            now = new Date();

            x.domain([now - (n - 2) * duration, now - duration]);
            y.domain([(-1)*d3.max(data) - 100, d3.max(data) + 100]);

            var d = random()
            data.push(d);

            // redraw the line
            svg.select(".line")
                .attr("d", line)
                .attr("transform", null);

            // slide the x-axis left
            axis.transition()
                .duration(duration)
                .ease("linear")
                .call(x.axis);

            // slide the line left
            path.transition()
                .duration(duration)
                .ease("linear")
                .attr("transform", "translate(" + x(now - (n - 1) * duration) + ")")
                .each("end", tick);

             circle.transition()
                   .duration(duration)
                   .ease("linear")
                   .attr("transform", "translate(0, " + y(d) + ")");

            // pop the old data point off the front
            data.shift();
        });

        this.tick();
    });

    GraphIndex();

HTML代码：

<div class="graph-holder"></div>

CSS代码：

.graph-holder {
position: relative;
width: 379px; height: 138px;
}
.x-axis line {
  shape-rendering: auto;
  stroke-width: 2px;
}
.x-axis path,
.x-axis line {
    fill: none;
    stroke: none;
    shape-rendering: crispEdges;
}
.x-axis .tick {
    color: #fff;
    stroke: #fff;
    font-size: .75em;
}
.line {
    fill: none;
    stroke: #fff;
    stroke-width: 2.5px;
}
circle {
    fill: #fff;
}

Answer 1

您是否尝试过调整圆的cy而不是平移它？ 您的Y轴未链接，因此无需变换坐标系。

所以代替

.attr("transform", "translate(0, " + y(d) + ")");

尝试

.attr("cy",  function() { return y(data[data.length-2]); });