如何使用toBase64Image()Chart.js 中的函式從下載的影像中洗掉不透明度？如果可能，保存為 JPG 而不是 PNG。這是代碼：
const myChart = new Chart(ctx, {
type: 'bar',
data: {
labels: ['Red', 'Blue', 'Yellow', 'Green', 'Purple', 'Orange'],
datasets: [{
label: '# of Votes',
data: [12, 19, 3, 5, 2, 3],
backgroundColor: [
'rgba(255, 99, 132, 0.2)',
'rgba(54, 162, 235, 0.2)',
'rgba(255, 206, 86, 0.2)',
'rgba(75, 192, 192, 0.2)',
'rgba(153, 102, 255, 0.2)',
'rgba(255, 159, 64, 0.2)'
],
borderColor: [
'rgba(255, 99, 132, 1)',
'rgba(54, 162, 235, 1)',
'rgba(255, 206, 86, 1)',
'rgba(75, 192, 192, 1)',
'rgba(153, 102, 255, 1)',
'rgba(255, 159, 64, 1)'
],
borderWidth: 1
}]
},
options: {
scales: {
y: {
beginAtZero: true
}
},
animation: {
onComplete: function() {
image = graficoConsumo.toBase64Image();
}
}
}
});
document.getElementById('btn-download-chart').onclick = function() {
// Trigger the download
var a = document.createElement('a');
a.href = image;
a.download = 'myChart.png';
a.click();
}
uj5u.com熱心網友回復：
不，默認情況下畫布沒有背景，因此它始終是透明的。為了解決這個問題，你可以撰寫一個小的自定義插件，在 chart.js 繪制它的東西之前繪制一個白色的背景：
Chart.register({
id: 'customBackground',
beforeDraw: (chart, args, opts) => {
const ctx = chart.canvas.getContext('2d');
ctx.save();
ctx.globalCompositeOperation = 'destination-over';
ctx.fillStyle = 'white';
ctx.fillRect(0, 0, chart.width, chart.height);
ctx.restore();
}
})
const options = {
type: 'line',
data: {
labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
datasets: [{
label: '# of Votes',
data: [12, 19, 3, 5, 2, 3],
borderColor: 'orange'
},
{
label: '# of Points',
data: [7, 11, 5, 8, 3, 7],
borderColor: 'pink'
}
]
},
options: {},
}
const ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);body {
background-color: black;
}<body>
<canvas id="chartJSContainer" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.6.2/chart.js"></script>
</body>轉載請註明出處，本文鏈接：https://www.uj5u.com/net/384245.html
標籤：javascript 查询 图表.js
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