我有多個畫布，這些畫布用作圖層。
canvas c1 = background image. canvas c2 = charactor image. canvas c3 = item image.
我的原始碼如下。
在同一位置設定三個畫布。
<div canvas="canvas-wrap">
<canvas class="canvas" id="c1">
<canvas class="canvas" id="c2">
<canvas class="canvas" id="c3">
</div>
.canvas-wrap{
width: 600px;
height:500px;
max-width: 100%;
position: relative;
padding: 0;
box-sizing: content-box;
}
.canvas{
position: absolute;
left:0;
top:0;
border: 0;
max-width:100%;
box-sizing: content-box;
padding: 0;
margin: 0;
}
現在，我想將這些畫布匯出為一張 jpg。
我有可以匯出一張畫布的原始碼，但我想從三張畫布中匯出一張jpg。
function saveCanvas(canvas_id)
{
var canvas = document.getElementById("c1");
var a = document.createElement('a');
a.href = canvas.toDataURL('image/jpeg', 0.85);
a.download = 'download.jpg';
a.click();
} 
這是可能的，但更好的方法是使用 1 個畫布並將所有內容繪製到那裡。
在這裡，我們創建一個虛擬畫布，循環遍歷所有畫布以將資料繪製到其上，然後保存該畫布生成的圖像。
//store all canvasses in array so we can loop through them later const canvasses = []; ['c1','c2','c3'].forEach(canvasId => { canvasses.push(document.getElementById(canvasId)); }); function save(){ //create one canvas to draw everything to const canvas = document.createElement("canvas"); canvas.width = canvasses[0].width; canvas.height = canvasses[0].height; //draw other canvases here const ctx = canvas.getContext('2d'); canvasses.forEach(data => { ctx.drawImage(data, 0, 0); }); //original saving code, using the fake canvas we created var a = document.createElement('a'); a.href = canvas.toDataURL('image/jpeg', 0.85); a.download = 'download.jpg'; a.click(); }