使用ChartJS BeforeDraw绘制时如何防止刻度标签“跳”

Question

This question builds on the previous question found here : ChartJS place y-axis labels between ticks .

When drawing the ticks with a BeforeDraw plugin, the ticks/labels end up "jumping" every time the canvas is redrawn. If you run the code snippet and look at the y-axis labels as you hover on and off of the bars, you will be able to see this "jumping".

Is there a way to prevent this "jumping" while still drawing the ticks with BeforeDraw?

 var barChart = new Chart(ctx, { type: 'bar', data: { labels: ['Jan', 'Feb', 'Mar'], datasets: [{ label: 'BAR', data: [10, 20, 30], backgroundColor: 'rgba(0, 119, 204, 0.5)' }] }, options: { responsive: false, scales: { yAxes: [{ ticks: { beginAtZero: true, "userCallback" : function(t, i){ var mapping_function = [ "", "Critical", "Needs Work", "Good", "Needs Work", "Getting There", "Great Choices"]; //return t; return mapping_function[mapping_function.length - (i + 1)]; }, } }] } }, plugins: [{ beforeDraw: function(chart) { var ctx = chart.ctx; var yAxis = chart.scales['y-axis-0']; var tickGap = yAxis.getPixelForTick(1) - yAxis.getPixelForTick(0); yAxis.options.ticks.fontColor = 'transparent'; // hide original tick // loop through ticks array Chart.helpers.each(yAxis.ticks, function(tick, index) { if (index === yAxis.ticks.length - 1) return; var xPos = yAxis.right; var yPos = yAxis.getPixelForTick(index); var xPadding = 10; // draw tick ctx.save(); ctx.textBaseline = 'middle'; ctx.textAlign = 'right'; ctx.fillStyle = 'rgba(0, 0, 0, 0.8)'; ctx.fillText(tick, xPos - xPadding, yPos + tickGap / 2); ctx.restore(); }); } }] }); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script> <canvas id="ctx" height="200"></canvas> 

Answer 1

Yes! there is a way. Use the following plugin :

plugins: [{
   beforeDraw: function(chart) {
      // hide original tick
      chart.scales['y-axis-0'].options.ticks.fontColor = 'transparent';
   },
   afterDraw: function(chart) {
      var ctx = chart.ctx;
      var yAxis = chart.scales['y-axis-0'];
      var tickGap = yAxis.getPixelForTick(1) - yAxis.getPixelForTick(0);
      // loop through ticks array
      Chart.helpers.each(yAxis.ticks, function(tick, index) {
         if (index === yAxis.ticks.length - 1) return;
         var xPos = yAxis.right;
         var yPos = yAxis.getPixelForTick(index);
         var xPadding = 10;
         // draw tick
         ctx.save();
         ctx.textBaseline = 'middle';
         ctx.textAlign = 'right';
         ctx.fillStyle = 'rgba(0, 0, 0, 0.8)';
         ctx.fillText(tick, xPos - xPadding, yPos + tickGap / 2);
         ctx.restore();
      });
   }
}]

demo ⧩

 var barChart = new Chart(ctx, { type: 'bar', data: { labels: ['Jan', 'Feb', 'Mar'], datasets: [{ label: 'BAR', data: [10, 20, 30], backgroundColor: 'rgba(0, 119, 204, 0.5)' }] }, options: { responsive: false, scales: { yAxes: [{ ticks: { beginAtZero: true, "userCallback": function(t, i) { var mapping_function = ["", "Critical", "Needs Work", "Good", "Needs Work", "Getting There", "Great Choices"]; //return t; return mapping_function[mapping_function.length - (i + 1)]; }, } }] } }, plugins: [{ beforeDraw: function(chart) { // hide original tick chart.scales['y-axis-0'].options.ticks.fontColor = 'transparent'; }, afterDraw: function(chart) { var ctx = chart.ctx; var yAxis = chart.scales['y-axis-0']; var tickGap = yAxis.getPixelForTick(1) - yAxis.getPixelForTick(0); // loop through ticks array Chart.helpers.each(yAxis.ticks, function(tick, index) { if (index === yAxis.ticks.length - 1) return; var xPos = yAxis.right; var yPos = yAxis.getPixelForTick(index); var xPadding = 10; // draw tick ctx.save(); ctx.textBaseline = 'middle'; ctx.textAlign = 'right'; ctx.fillStyle = 'rgba(0, 0, 0, 0.8)'; ctx.fillText(tick, xPos - xPadding, yPos + tickGap / 2); ctx.restore(); }); } }] }); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script> <canvas id="ctx" height="200"></canvas>