javascript - canvas.drawImage 没有绘制所有图像

Question

我想在 Canvas 上绘制多个图像(背景，背景上的另一个图像， 然后在该图像上再次出现另一个图像)， 但有时它会加载图像，有时不会， 我使用 setTimeout 来延迟绘制图像和加载，但它仍然不起作用。

if(somecondition)
{
    //background image is 70kb
    //image on background is 65kb

    img3.src = "Image  path"; //images is almost 2kb 
    img4.src = "Image  path"; //images is almost 2kb 
    img5.src = "Image  path"; //images is almost 2kb 
    img6.src = "Image  path"; //images is almost 2kb 
    setTimeout(function()
    {
        img3.onload = function() 
        {
          context.drawImage(img3, 272, 139, 172, 31);
        }
    },1000);
    console.log("Linesss2 > 4 "+lines2);
    bottomY = 290+((lines1-5)*10);
    middleHeight = bottomY - 170;




    setTimeout(function()
    {
        img4.onload = function() 
        {
          context.drawImage(img4, 272, 170, 172, middleHeight);  ///272
        }
        img6.onload = function() 
        {
          context.drawImage(img6, 272, bottomY, 172, 71);
        }
    },1000);

    }
    var metrics1 = context.measureText(canvasText1);
    var testWidth1 = metrics1.width;

    var metrics2 = context.measureText(canvasText2);
    var testWidth2 = metrics2.width;

    context.fillText(canvasText1, 169.5-(testWidth/2), y-20);
    context.fillText(canvasText2, 169.5-(testWidth/2), y-20);
    wrapTextForCanvas1(context, canvasText1, 50, 180);
    wrapTextForCanvas2(context, canvasText2, 260, 180);
}

Answer 1

因此，您不想运行任意超时，您希望在每个图像加载时收到通知。这样您就可以在开始尝试使用它们之前确定它们都已加载。只需设置每个图像的 onload 回调，使其递增一个计数器。当该计数器达到您必须加载的图像数量时，它们就全部完成了，您可以开始使用它们了。

我最近回答了另一个问题。修改后的代码见这里: http://jsfiddle.net/enhzflep/RLP5Y/

或此处为问题本身:Images from previous functions are not drawn in the background (Canvas)