我正在使用Chart.js,并希望将一张线状图转换为PNG格式。问题在于,该图像总是以透明的背景下载,这不是我想要的。我尝试了很多选项,但都没有真正起作用。
有什么建议吗?
有什么建议吗?
这里有一个完美运作的解决方案,即使保存为图像文件(如png)也可以。我从@etimberg在chartjs问题追踪器中公开抄袭了这个解决方案。
Chart.plugins.register({
beforeDraw: function(chartInstance) {
var ctx = chartInstance.chart.ctx;
ctx.fillStyle = "white";
ctx.fillRect(0, 0, chartInstance.chart.width, chartInstance.chart.height);
}
});
这段内容应该在你的源代码中图表之前显示。
onAnimationComplete
属性添加到图表中来实现此目的。onAnimationComplete
函数中:
drawImage
ChartJS画布覆盖在填充了白色的temp画布上。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();
}
});
这里是示例代码和演示:
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>
$('#myChart').css('background-color', 'rgba(0, 0, 0, 0)'); // this worked for me but I'm guessing you can set a background image using css like you normally do.
如果你愿意更改chart.js中的代码,那么你可以很容易地解决这个问题。
在chart.js中有一个名为clear的函数。你可以通过搜索clearRect来找到它。每次chart.js重新绘制图表时都会调用clear函数,因此我们将在该函数下方设置背景。在带有clearRect的行的下面添加以下行。
...
chart.ctx.clearRect(0,0,chart.width,chart.height);
// Add these 3 lines
chart.ctx.rect(0, 0, chart.width, chart.height);
chart.ctx.fillStyle="#fff"; // Put your desired background color here
chart.ctx.fill();
...