目标是创建具有多个轨迹的平滑滚动实时图。
我能够为单个跟踪执行此操作,但是当我添加更多行进行过渡时,动画似乎变得一团糟。我有一种感觉,过渡正在循环和碰撞,但我不知道如何防止这种情况发生。
如果您N_CH = 1
在代码段中进行设置,则事情运行顺利。当它设置为N_CH = 4
然后动画变得生涩(似乎过渡没有完全完成)并且(有趣的是)x 轴滚动似乎变得比 时快 4 倍N_CH = 1
。
您可以通过更改tick()
函数中的变换以匹配通道数(即iScale(-4)
for N_CH = 4
)来恢复平滑度,但这不是“正确的”,因为翻译速度人为地快。最后,我需要实时准确的时间测量。
我尝试了各种不同的方法,包括:
data
对象并允许d3
通过selectAll()
调用遍历数据结构……结果似乎总是一样。
// set up some variables
const N_CH = 4;
const N_PTS = 40;
const margin = {top: 20, right: 30, bottom: 30, left: 40};
const width = 800;
const height = 300;
const colors = ['steelblue', 'red', 'orange', 'magenta']
// instantiate data array (timestamps)
var data = [];
var channelData = [];
for (let ch = 0; ch < N_CH; ch++) {
channelData = [];
for (let i = 0; i < N_PTS; i++) {
channelData.push({
x: Date.now() + i * 1000,
y: ch + Math.random()
})
}
data.push({
name: "CH" + ch,
values: channelData
});
}
// initialize //////////////////////////////
// instantiate svg and attach to DOM element
var svg = d3
.select("#chart")
.append("svg")
.attr("viewBox", `0 0 ${width} ${height}`)
// add clip path for smooth entry/exit
svg.append("defs").append("clipPath")
.attr("id", "clip")
.append("rect")
.attr("x", margin.left)
.attr("y", margin.bottom)
.attr("width", width - margin.left - margin.right)
.attr("height", height - margin.top - margin.bottom);
// set index scale for data buffer position/transition
var iScale = d3.scaleLinear()
.range([0, width - margin.right])
.domain([0, data[0].values.length - 1]);
// set up x-axis scale for data x units (time)
var xScale = d3.scaleUtc()
.range([margin.left, width - margin.right])
// add x-axis to svg
var xAxis = svg.append("g")
.attr("class", "x-axis")
.attr("transform", `translate(0, ${height - margin.top})`)
.call(d3.axisBottom(xScale));
// set up y-axis
var yScale = d3.scaleLinear()
.range([height - margin.top, margin.bottom]);
// add y-axis to svg
var yAxis = svg.append("g")
.attr("class", "y-axis")
.attr("transform", `translate(${margin.left}, 0)`)
.call(d3.axisLeft(yScale));
// set the domains
xScale.domain(d3.extent(this.data[0].values, d => d.x));
// get global y domain
var flatten = [].concat.apply([], data.map(o => o.values))
yScale.domain(d3.extent(flatten, d => d.y));
// define the line
var line = d3.line()
.x((d, i) => iScale(i))
.y(d => yScale(d.y));
// make a group where we will append our paths
traces = svg.append("g")
.attr("clip-path", "url(#clip)")
for (let ch=0; ch<N_CH; ch++) {
traces.append("path")
.datum(data[ch].values)
.attr("id", `trace-${ch}`)
.attr("class", "trace")
.attr("d", line)
.attr("stroke", colors[ch])
.attr("fill", "none")
.attr("stroke-width", 1.5)
.attr("transform", "translate(0)")
}
// end initialize ////////////////////
// animate
tick();
function tick() {
// add data to buffer
let lastData;
for (let ch = 0; ch < N_CH; ch++) {
lastData = data[ch].values[data[ch].values.length - 1];
data[ch].values.push({
x: lastData.x + 1000,
y: ch + Math.random()
});
}
// update individual trace path data
for (let ch = 0; ch < N_CH; ch++) {
traces.select(`#trace-${ch}`)
.attr("d", line)
}
// animate transition
traces
.selectAll('.trace')
.attr("transform", "translate(0)")
.transition().duration(1000).ease(d3.easeLinear)
.attr("transform", `translate(${iScale(-1)}, 0)`)
.on("end", tick)
// update the domain
xScale.domain(d3.extent(data[0].values, d => d.x));
// animate/redraw axis
xAxis
.transition().duration(1000).ease(d3.easeLinear)
.call(d3.axisBottom(xScale));
for (let ch=0; ch<N_CH; ch++) {
data[ch].values.shift();
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>
<div id="chart"></div>
这里有几个问题:
您根据 iScale 绘制数据,但根据 xScale 绘制轴:这里立即存在差异:每个比例的范围不同。但是没有理由不应该对两者使用相同的比例:这样您就不会在绘图和轴之间有任何差异。如果您删除剪辑路径并删除刻度函数,您会注意到您的线条最初并未呈现在您期望的位置:
D3 的转换事件侦听器用于每个转换。您正在转换许多元素,这会在每一行完成时触发。因此,在四行第一次完成转换后,您触发了四次刻度函数:这会导致各种混乱,因为该函数旨在被调用一次以一次转换所有行。
在重新阅读这个问题时,您发现了调用刻度函数 4x 而不是一次的问题:
您可以通过更改 tick() 函数中的变换以匹配通道数(即 N_CH = 4 的 iScale(-4))来恢复平滑度,但这不是“正确的”,因为转换速度人为地快速。
如果我们解决这个问题以便我们调用一次 tick 函数,当所有的线转换完成后,我们就解决了平滑问题:
// set up some variables
const N_CH = 4;
const N_PTS = 40;
const margin = {top: 20, right: 30, bottom: 30, left: 40};
const width = 800;
const height = 300;
const colors = ['steelblue', 'red', 'orange', 'magenta']
// instantiate data array (timestamps)
var data = [];
var channelData = [];
for (let ch = 0; ch < N_CH; ch++) {
channelData = [];
for (let i = 0; i < N_PTS; i++) {
channelData.push({
x: Date.now() + i * 1000,
y: ch + Math.random()
})
}
data.push({
name: "CH" + ch,
values: channelData
});
}
// initialize //////////////////////////////
// instantiate svg and attach to DOM element
var svg = d3
.select("#chart")
.append("svg")
.attr("viewBox", `0 0 ${width} ${height}`)
// add clip path for smooth entry/exit
svg.append("defs").append("clipPath")
.attr("id", "clip")
.append("rect")
.attr("x", margin.left)
.attr("y", margin.bottom)
.attr("width", width - margin.left - margin.right)
.attr("height", height - margin.top - margin.bottom);
// set index scale for data buffer position/transition
var iScale = d3.scaleLinear()
.range([0, width - margin.right])
.domain([0, data[0].values.length - 1]);
// set up x-axis scale for data x units (time)
var xScale = d3.scaleUtc()
.range([margin.left, width - margin.right])
// add x-axis to svg
var xAxis = svg.append("g")
.attr("class", "x-axis")
.attr("transform", `translate(0, ${height - margin.top})`)
.call(d3.axisBottom(xScale));
// set up y-axis
var yScale = d3.scaleLinear()
.range([height - margin.top, margin.bottom]);
// add y-axis to svg
var yAxis = svg.append("g")
.attr("class", "y-axis")
.attr("transform", `translate(${margin.left}, 0)`)
.call(d3.axisLeft(yScale));
// set the domains
xScale.domain(d3.extent(this.data[0].values, d => d.x));
// get global y domain
var flatten = [].concat.apply([], data.map(o => o.values))
yScale.domain(d3.extent(flatten, d => d.y));
// define the line
var line = d3.line()
.x((d, i) => iScale(i))
.y(d => yScale(d.y));
// make a group where we will append our paths
traces = svg.append("g")
.attr("clip-path", "url(#clip)")
for (let ch=0; ch<N_CH; ch++) {
traces.append("path")
.datum(data[ch].values)
.attr("id", `trace-${ch}`)
.attr("class", "trace")
.attr("d", line)
.attr("stroke", colors[ch])
.attr("fill", "none")
.attr("stroke-width", 1.5)
.attr("transform", "translate(0)")
}
// end initialize ////////////////////
// animate
tick();
function tick() {
// add data to buffer
let lastData;
for (let ch = 0; ch < N_CH; ch++) {
lastData = data[ch].values[data[ch].values.length - 1];
data[ch].values.push({
x: lastData.x + 1000,
y: ch + Math.random()
});
}
// update individual trace path data
for (let ch = 0; ch < N_CH; ch++) {
traces.select(`#trace-${ch}`)
.attr("d", line)
}
// animate transition
traces
.selectAll('.trace')
.attr("transform", "translate(0)")
.transition().duration(1000).ease(d3.easeLinear)
.attr("transform", `translate(${iScale(-1)}, 0)`)
.end().then(tick);
// update the domain
xScale.domain(d3.extent(data[0].values, d => d.x));
// animate/redraw axis
xAxis
.transition().duration(1000).ease(d3.easeLinear)
.call(d3.axisBottom(xScale));
for (let ch=0; ch<N_CH; ch++) {
data[ch].values.shift();
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/7.0.0/d3.min.js"></script>
<div id="chart"></div>
在上面我使用 transition.end() 在所有选定的元素完成转换时返回一个承诺。我已经升级了您的 D3 版本,因为这是一个较新的功能:
.end().then(tick);
您的代码使用循环来附加和修改元素。这会产生额外的开销:在 DOM 中选择元素需要时间,您必须识别每一行以便您可以再次重新选择它,并且您必须在绑定数据方面做一些额外的工作。让我们用 d3 输入/更新周期来简化它:
创建要开始的行:
let lines = traces.selectAll(null)
.data(data)
.enter()
.append("path")
.attr("d", d=>line(d.values))
.attr("stroke", (d,i)=>colors[i])
.attr("fill", "none")
.attr("stroke-width", 1.5)
.attr("transform","translate(0,0)");
现在在 update/tick 函数中,我们可以轻松修改绑定数据:
lines.each(function(d,i) {
d.values.push({
x: d.values[d.values.length-1].x + dt,
y: i + Math.random()
})
})
.attr("d", d=>line(d.values))
我们可以删除每行的第一个数据点:
lines.each(d=>d.values.shift());
一般来说,(显式)循环在使用 D3 操作 SVG 元素时非常罕见,因为它与 D3 的设计原则背道而驰。有关为什么这很重要以及它如何有用的一些讨论,请参见此处。
连同移除 iScale 并使用 transition.end(),我们可能会得到类似的结果:
// set up some variables
const N_CH = 4;
const N_PTS = 40;
const margin = {top: 20, right: 30, bottom: 30, left: 40};
const width = 800;
const height = 300;
const colors = ['steelblue', 'red', 'orange', 'magenta']
// instantiate data array (timestamps)
var data = [];
var channelData = [];
for (let ch = 0; ch < N_CH; ch++) {
channelData = [];
for (let i = 0; i < N_PTS; i++) {
channelData.push({
x: Date.now() + i * 1000,
y: ch + Math.random()
})
}
data.push({
name: "CH" + ch,
values: channelData
});
}
// initialize //////////////////////////////
// instantiate svg and attach to DOM element
var svg = d3
.select("#chart")
.append("svg")
.attr("viewBox", `0 0 ${width} ${height}`)
// add clip path for smooth entry/exit
svg.append("defs").append("clipPath")
.attr("id", "clip")
.append("rect")
.attr("x", margin.left)
.attr("y", margin.bottom)
.attr("width", width - margin.left - margin.right)
.attr("height", height - margin.top - margin.bottom);
// set up x-axis scale for data x units (time)
var xScale = d3.scaleTime()
.range([margin.left, width - margin.right])
.domain(d3.extent(data[0].values,d=>d.x))
// add x-axis to svg
var xAxis = svg.append("g")
.attr("class", "x-axis")
.attr("transform", `translate(0, ${height - margin.top})`)
.call(d3.axisBottom(xScale));
// set up y-axis
var yScale = d3.scaleLinear()
.range([height - margin.top, margin.bottom]);
// add y-axis to svg
var yAxis = svg.append("g")
.attr("class", "y-axis")
.attr("transform", `translate(${margin.left}, 0)`)
.call(d3.axisLeft(yScale));
// set the domains
xScale.domain(d3.extent(this.data[0].values, d => d.x));
// get global y domain
var flatten = [].concat.apply([], data.map(o => o.values))
yScale.domain(d3.extent(flatten, d => d.y));
// define the line
var line = d3.line()
.x(d => xScale(d.x))
.y(d => yScale(d.y));
// make a group where we will append our paths
traces = svg.append("g")
.attr("clip-path", "url(#clip)")
// Create lines:
let lines = traces.selectAll(null)
.data(data)
.enter()
.append("path")
.attr("d", d=>line(d.values))
.attr("stroke", (d,i)=>colors[i])
.attr("fill", "none")
.attr("stroke-width", 1.5)
.attr("transform","translate(0,0)");
transition();
function transition() {
let dt = 1000; // difference in time.
let dx = xScale(d3.timeMillisecond.offset(xScale.domain()[0],dt)) - xScale.range()[0]; // difference in pixels.
lines.each(function(d,i) {
d.values.push({
x: d.values[d.values.length-1].x + dt,
y: i + Math.random()
})
})
.attr("d", d=>line(d.values))
.transition()
.duration(1000)
.attr("transform",`translate(${-dx}, 0)`)
.ease(d3.easeLinear)
.end().then(function() {
lines.each(d=>d.values.shift())
.attr("transform","translate(0,0)")
transition();
})
xScale.domain(xScale
.domain()
.map(d=>d3.timeMillisecond.offset(d,dt)))
xAxis
.transition().duration(1000).ease(d3.easeLinear)
.call(d3.axisBottom(xScale))
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/7.0.0/d3.min.js"></script>
<div id="chart"></div>
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