load image to fabric canvas background

问题:

hi im trying to upload an image and put it as canvas background. code snippet:

function handleMenuImage(e){
    var reader = new FileReader();
    reader.onload = function(event){
        var img = new Image();
        img.src = event.target.result;
        canvas.setWidth(img.width);
        canvas.setHeight(img.height);
        canvas.setBackgroundImage(img.src, canvas.renderAll.bind(canvas));

        //set the page background
        menuPages[currentPage].pageBackground.src = img.src;
        canvas.backgroundImageStretch = false;

    }
    reader.readAsDataURL(e.target.files[0]); 
}

the problem is that the canvas not showing the background. i can see the canvas background src in chrome devtools. the background is actually have been set but somehow its not displayed.

回答1:

That seems strangely confusing. If you want a background image on an HTMLCanvasElement, why not just set the background image via CSS?

#myCanvas {
  background-image: url(http://placekitten.com/100/100);
}

Or set the CSS via JavaScript:

canvas.style.backgroundImage = 'url(http://placekitten.com/100/100)';

回答2:

Try the following code:

var raw_reader = new FileReader();
raw_reader.onload = function (event){
  var reader = new FileReader();
  reader.onload = function(event){
    var img = new Image();
    img.src = event.target.result;
    canvas.setWidth(img.width);
    canvas.setHeight(img.height);
    canvas.setBackgroundImage(img.src, canvas.renderAll.bind(canvas));

    //set the page background
    menuPages[currentPage].pageBackground.src = img.src;
    canvas.backgroundImageStretch = false;

  }
  reader.readAsDataURL(e.target.files[0]); 
}
raw_reader.readAsBinaryString(e.target.files[0]);