Image converted to Base64 not showing on bootstrap modal's canvas

问题

I am taking the Image from user,performing the crop operation, converting it to base64 and then drawing it on a canvas. For the cropping I am using jcrop library.

$(document).on("change","#photograph",function() {
   $("#picCrop").modal('show'); 
   $("#views").empty(); 

   image = null;
   canvas = null;
   alert("canvas"+(canvas==null)+" Image"+ (image==null));

   loadImage(this);
   $(this).replaceWith('<input id="photograph" type="file"    class="form-control">');
});

Here I am facing the issue, without alert("canvas"+(canvas==null)+" Image"+ (image==null)); the image is not visible on canvas, in case of large images it is getting rendered only if I wait for some time before hitting the alert box button.

fiddle link: https://jsfiddle.net/govi20/spmc7ymp/5/ (comment out the alert line to check the result)

回答1:

The problem here is that the image loading for firefox needs typically have the correct size already before moving on to the next step. And the modal needs to exist for the canvas to be attached to that.

https://jsfiddle.net/a0e5dt98/

$(document).on("change", "#photograph", function() {
  $(this).replaceWith('<input id="photograph" type="file" class="form-control">');
  $("#picCrop").modal('show');
  loadImage(this);
});

$('#picCrop').on('shown.bs.modal', function(e) {
  validateImage();
})

Then it calls loadImage from the selection of the image. Then validates that image on the loading of the modal which will affix it to the now existing div. This does assume that the imageLoad takes less time than the modal loading. In theory you might be able to load a large enough image locally that it can't validate the unloaded image.

Then dividing up the validate and the affix again, so that firefox can get the sizes correctly.

function validateImage() {
  console.log("validateimage.")
  if (canvas != null) {
    image = new Image();
    image.onload = affixJcrop;
    image.src = canvas.toDataURL('image/png');
  } else affixJcrop();
}

function affixJcrop() {
  console.log("affixJcrop")
  if (jcrop_api != null) {
    jcrop_api.destroy();
  }
  $("#views").empty();
  $("#views").append("<canvas id=\"canvas\">");
  canvas = $("#canvas")[0];
  context = canvas.getContext("2d");
  console.log(image.width);
  console.log(image.height);
  canvas.width = image.width;
  canvas.height = image.height;
  context.drawImage(image, 0, 0);
  $("#canvas").Jcrop({
    onSelect: selectcanvas,
    onRelease: clearcanvas,
    boxWidth: crop_max_width,
    boxHeight: crop_max_height,
    minSize: [100, 100],
    setSelect: [0, 0, 100, 100]
  }, function() {
    jcrop_api = this;
  });
  clearcanvas();
}

来源：https://stackoverflow.com/questions/37828355/image-converted-to-base64-not-showing-on-bootstrap-modals-canvas

标签

javascript

jquery

html

canvas

jcrop