chartjs how to apply after animation - chart.js

Question

trying to extend a chart, so that i can draw lines up to the data point, but this is happening before the default animation. it would look smoother if it applied after.
i have got most of it to work.. but how do i get this to apply after chart animation.
var originalLineDraw = Chart.controllers.line.prototype.draw;
Chart.helpers.extend(Chart.controllers.line.prototype, {
draw: function () {
originalLineDraw.apply(this, arguments);
var chart = this.chart;
var ctx = chart.chart.ctx;
var index = chart.config.data.lineAtIndex;
if (index) {
var xaxis = chart.scales['x-axis-0'];
var yaxis = chart.scales['y-axis-1']
var points = this.chart.getDatasetMeta(this.index).data;
for (var i = 0; i < points.length; i++) {
// var point_x = points[i]._model.x;
var point_y = points[i]._model.y;
ctx.beginPath();
ctx.setLineDash([5, 5]);/*dashes are 5px and spaces are 3px*/
ctx.moveTo(xaxis.getPixelForValue(undefined, i), point_y);
ctx.strokeStyle = '#fff';
ctx.lineTo(xaxis.getPixelForValue(undefined, i), yaxis.bottom);
ctx.stroke();
}
}
}
});
Update...
altho the darw is incorrect it still is playing after animation
var verticalLinePlugin = {
renderVerticalLine: function (chartInstance) {
var chart = chartInstance;
var ctx = chart.chart.ctx;
var maxpoint = [];
//loop the datasets
for (var y = 0; y < chart.config.data.datasets.length; y++) {
var dataset = chart.config.data.datasets[y];
if (dataset.hidden)
continue;
var points = chart.getDatasetMeta(y).data;
for (var i = 0; i < points.length; i++) {
var point_y = points[i]._model.y;
if (point_y < 0)
continue;
var point = maxpoint[i];
if (point == undefined) {
maxpoint.push({ id: i, y: point_y });
} else {
if (point.y > point_y) {
point.y = point_y;
}
}
}
}
var xaxis = chart.scales['x-axis-0'];
var yaxis = chart.scales['y-axis-1']
chart.data.datasets.forEach(function (dataset, i) {
var ds = dataset;
var meta = chart.getDatasetMeta(i);
meta.data.forEach(function (element, index) {
var value = maxpoint[i];
ctx.beginPath();
ctx.setLineDash([5, 5]);
ctx.moveTo(xaxis.getPixelForValue(undefined, i), value.y);
ctx.strokeStyle = '#fff';
ctx.lineTo(xaxis.getPixelForValue(undefined, i), yaxis.bottom);
ctx.stroke();
});
});
},
afterRender: function (chart) {
this.renderVerticalLine(chart);
}
};
Chart.plugins.register(verticalLinePlugin);

Answer 1

I made some small changes (non-intuitive!), and the vertical lines now appear after the animation.
Get the x values from the metadata instead of the data.
Either:
var x_point = element._model.x;
or:
var position = element.tooltipPosition();
var x_point = position.x;
Wrap the drawing in if(!hidden){}, then the vertical lines will disapear and reappear with the data. (The ternary assignment fixes a clash if the data starts hidden)
Do you need the value=max[i]? If just drawing the line up to the points, can get the y_point the same as for x.
var xaxis = chart.scales['x-axis-0'];
var yaxis = chart.scales['y-axis-1'];
chart.data.datasets.forEach(function (dataset, i) {
var meta = chart.getDatasetMeta(i);
var hidden = (meta.hidden != undefined) ? meta.hidden : dataset.hidden
if(!hidden){
meta.data.forEach(function (element, index) {
//var value = maxpoint[i];
var x_point = element._model.x;
var y_point = element._model.y;
ctx.beginPath();
ctx.save();
ctx.setLineDash([5, 5])
ctx.strokeStyle = '#fff';
ctx.moveTo(x_point, y_point); // or value.y
ctx.lineTo(x_point, yaxis.bottom)
ctx.stroke();
ctx.restore();
});
}
});