[英]How put over the dot a image, in a canvas?
如何在每個對象中放置圖像?
目前只有它的顯示點,但我需要顯示圖像
for (var i = 0; i < objects.length; i++) {
var object = objects[i];
object.y += spawnRateOfDescent;
ctx.beginPath();
ctx.arc(object.x, object.y, 8, 0, Math.PI * 2);
ctx.closePath();
ctx.fillStyle = object.type;
ctx.fill();
}
我試過這個
var img = new Image();
img.src = "img/HannyahNED/Cohete_1"+".png";
img.onload = function () {
ctx.drawImage(img, object.x, object.y);
};
但不起作用
關鍵思想是加載圖像是異步的。 下面的代碼片段首先加載圖像(通過創建一個 promise 來解決image.onload
完成)。
之后,您的代碼工作正常。
const canvas = document.querySelector('canvas') const ctx = canvas.getContext('2d') const objects = [{ x: 10, y: 10, src: "https://via.placeholder.com/60/FF0000" // red image }, { x: 90, y: 90, src: "https://via.placeholder.com/60/00FF00" // green image }, { x: 170, y: 170, src: "https://via.placeholder.com/60/0000FF" // blue image } ] function fetchImage(url) { return new Promise(resolve => { const img = new Image(); img.src = url; img.onload = () => resolve(img); }); } const promises = objects.map(object => { return fetchImage(object.src).then(img => object.img = img) }); Promise.all(promises).then(() => { objects.forEach(object => { ctx.drawImage(object.img, object.x, object.y); ctx.beginPath(); ctx.arc(object.x, object.y, 8, 0, Math.PI * 2); ctx.closePath(); ctx.fill(); }); })
<div> <canvas width="400" height="400"></canvas> </div>
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