Chart.js折线图设置背景颜色 [英] Chart.js line chart set background color

问题描述

我正在使用Chart.js并希望将折线图转换为PNG。问题是图像总是以透明背景下载，这不是我需要的。我尝试了很多选项，没有真正有效。

I'm working with Chart.js and want to convert a line chart to a PNG. The problem is that the image always downloads with a transparent background, which is not what I need. I tried many options, nothing really worked.

和建议？

推荐答案

以下是获取ChartJS完全不透明版本的一种方法：

等待图表完全动画完成。您可以通过将 onAnimationComplete 属性添加到图表中来实现此目的。

Wait until the chart is fully animated out and complete. You can do this by adding the onAnimationComplete property to the chart.

在 onAnimationComplete中 function：

In the onAnimationComplete function:

• 创建一个与图表大小相同的内存临时画布。


• 用白色填充临时画布


• drawImage ChartJS画布在白色填充的临时画布上


• 从临时画布创建一个图像。

• Create an in-memory temporary canvas of equal size as your chart.
• Fill the temp canvas with white
• drawImage the ChartJS canvas over the white-filled temp canvas
• Create an image from the temp canvas.

以下是如何做到的：

var ctx = document.getElementById("canvas").getContext("2d");
window.myLine = new Chart(ctx).Line(lineChartData, {
  responsive: true,
  onAnimationComplete:function(){
      var tcanvas=document.createElement('canvas');
      var tctx=tcanvas.getContext('2d');
      tcanvas.width=ctx.canvas.width;
      tcanvas.height=ctx.canvas.height;
      tctx.fillStyle='white';
      tctx.fillRect(0,0,tcanvas.width,tcanvas.height);
      tctx.drawImage(canvas,0,0);
      var img=new Image();
      img.onload=function(){
          document.body.appendChild(img);
      }
      img.src=tcanvas.toDataURL();
  }
});

以下是示例代码和演示：

var randomScalingFactor = function(){ return Math.round(Math.random()*100)};

var randomColorFactor = function(){ return Math.round(Math.random()*255)};

var lineChartData = {
  labels : ["January","February","March","April","May","June","July"],
  datasets : [
    {
      label: "My First dataset",
      fillColor : "rgba(220,220,220,0.2)",
      strokeColor : "rgba(220,220,220,1)",
      pointColor : "rgba(220,220,220,1)",
      pointStrokeColor : "#fff",
      pointHighlightFill : "#fff",
      pointHighlightStroke : "rgba(220,220,220,1)",
      data : [randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor()]
    },
    {
      label: "My Second dataset",
      fillColor : "rgba(151,187,205,0.2)",
      strokeColor : "rgba(151,187,205,1)",
      pointColor : "rgba(151,187,205,1)",
      pointStrokeColor : "#fff",
      pointHighlightFill : "#fff",
      pointHighlightStroke : "rgba(151,187,205,1)",
      data : [randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor(),randomScalingFactor()]
    }
  ]

}

var ctx = document.getElementById("canvas").getContext("2d");
window.myLine = new Chart(ctx).Line(lineChartData, {
  responsive: true,
  onAnimationComplete:function(){
    var tcanvas=document.createElement('canvas');
    var tctx=tcanvas.getContext('2d');
    tcanvas.width=ctx.canvas.width;
    tcanvas.height=ctx.canvas.height;
    tctx.fillStyle='white';
    tctx.fillRect(0,0,tcanvas.width,tcanvas.height);
    tctx.drawImage(canvas,0,0);
    var img=new Image();
    img.onload=function(){
      document.body.appendChild(img);
    }
    img.src=tcanvas.toDataURL();
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/1.0.2/Chart.min.js"></script>
<h4>ChartJS line chart</h4>
<div style="width:30%">
  <div>
    <canvas id="canvas" height="450" width="600"></canvas>
  </div>
</div>
<h4>Fully opaque chart as image</h4>

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