javascript - Placing a dot on an image - onClick

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javascript - Placing a dot on an image - onClick

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

A user will be able to click on 3 points on an image, and i want to display a BLACK dot at those points. Then i will save these values in my database, and regenerate the image with those 3 points later on.

This is a 2 part question:

1.) In my code, i am not able to detect the onClick event when the image is clicked. Can someone look into this. Here's my code. JSFIDDLE

  $(document).ready(function () {
      $('body').click(function (ev) {
          alert("d");
          mouseX = ev.pageX;
          mouseY = ev.pageY
          alert(mouseX + ' ' + mouseY);
          var color = '#000000';
          var size = '1px';
          $("body").append(
          $('<div></div>')
              .css('position', 'absolute')
              .css('top', mouseY + 'px')
              .css('left', mouseX + 'px')
              .css('width', size)
              .css('height', size)
              .css('background-color', color));
      });
  });

HTML

<body background="http://www.craigjoneswildlifephotography.co.uk/blog/wp-content/uploads/2010/07/CMJ57311.jpg">

</body>

2.) Say that i have the X and Y coordinates of the points, and how can i regenerate the image with those points ?

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1 Answer

深蓝 · Answer 1 · 2021-10-23T20:03:32+0000

Just use document instead of body (your body element has a calculated height of 0, but document is always the full size of the window):

http://jsfiddle.net/TrueBlueAussie/95vczfve/5/

  $(document).ready(function () {
      $(document).click(function (ev) {
          mouseX = ev.pageX;
          mouseY = ev.pageY
          console.log(mouseX + ' ' + mouseY);
          var color = '#000000';
          var size = '1px';
          $("body").append(
          $('<div></div>')
              .css('position', 'absolute')
              .css('top', mouseY + 'px')
              .css('left', mouseX + 'px')
              .css('width', size)
              .css('height', size)
              .css('background-color', color));
      });
  });

As a side note: Your original JSFiddle is also a great example of why you should not connect delegated events to body instead of document. The body element can be styled out of existence (also document exists before the DOM is even loaded) :)

Or, as Brian provided, a reduced version http://jsfiddle.net/BrianDillingham/95vczfve/7/:

$(document).ready(function(){ 

    $(document).click(function (ev) {        
        $("body").append(            
            $('<div></div>').css({
                position: 'absolute',
                top: ev.pageY + 'px',
                left: ev.pageX + 'px',
                width: '10px',
                height: '10px',
                background: '#000000'
            })              
        );               
    });

});

And Brian's final update with limit of 3 dots: http://jsfiddle.net/BrianDillingham/95vczfve/8/

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