Canvas image zoom and crop feature ensures fixed selection area across all platforms

Question

Canvas image zoom and crop feature ensures fixed selection area across all platforms

After finding inspiration from a source I cannot name, I developed a plugin that allows for image cropping on both mobile and desktop devices.

The key features of my plugin include touch support, dynamic canvas sizing based on image dimensions, and the ability to move an image rather than just selecting an area. I initially considered purchasing a similar plugin but it did not meet my requirements when tested on different devices, prompting me to customize my own version.

You can view the working demo on JSFiddle.

This is the HTML structure:

<div class="container">
   <canvas id="panel" width="779" height="519"></canvas>
</div>

<input type="button" value="crop Selection" id="crop-image" />

<img id="croppedSelection" height="100px" width="100px" />

To initialize the plugin:

var Cropper = new CanvasCrop(document.getElementById('panel'), 'http://www.script-tutorials.com/demos/197/images/image.jpg');

$('#crop-image').on('click', function(){
   var src = Cropper.getBase64();
   $('#croppedSelection').attr('src', src);
});

I am now facing a challenge - how can I ensure that the selection area remains visible on the screen even when the parent image is scrolled, similar to the functionality seen here.

Any help or advice on this matter would be greatly appreciated.

As the source code is too extensive to include here, you can refer to the JSFiddle for a full demonstration. Thank you.

Edit

An updated version of the demo with fixed canvas height and width issues can be found on JSFiddle.

javascript

Answer 1

Answer №1

On a lazy afternoon, I found myself jotting down this code out of sheer boredom.

To implement this functionality, make sure to include the specified class in your code snippet. However, if you only require one viewer on the page, it's not necessary to use the class - everything can be encapsulated within a simple object. Should you need more viewers, consider the following:

function galleryViewer (html_viewer)
    {
    this.html_viewer=html_viewer;
    Object.defineProperty(html_viewer,"viewer_instance",{writeable:false,configureable:false,enumerable:false,value:this});
    this.selections = new Array ();
    html_viewer.addEventListener("mousedown",this.startScrolling);
    html_viewer.addEventListener("mouseup", this.endScrolling);
    html_viewer.addEventListener("scroll",this.setSelectionPosition);
    }

galleryViewer.prototype.startScrolling=function ()
    {
    var selections=this.viewer_instance.selections, selection;
    var l=selections.length;

    for (var i=0;i<l;i++)
        {
        selection=selections[i];
        selection.startLeft=selection.x;
        selection.startTop=selection.y;
        selection.viewer_startScrollLeft=this.scrollLeft;
        selection.viewer_startScrollTop=this.scrollTop;
        }
   }

galleryViewer.prototype.setSelectionPosition=function ()
  {
  var selections=this.viewer_instance.selections, selection;
  var l=selections.length;
  
  for (var i=0;i<l;i++)
    {
    selection=selections[i];
    selection.x=this.scrollLeft-selection.viewer_startScrollLeft+selection.startLeft;
    selection.y=this.scrollTop-selection.viewer_startScrollTop+selection.startTop;
    }

  this.viewer_instance.drawScene();
  }

 galleryViewer.prototype.endScrolling=function ()
   {
   var selections=this.viewer_instance.selections, selection;
   var l=selections.length;

   for (var i=0;i<l;i++)
     {
     selection=selections[i];
     selection.startLeft=null;
     selection.startTop=null;
     selection.viewer_startScrollLeft=null;
     selection.viewer_startScrollTop=null;
     }
   }

 galleryViewer.prototype.addSelection=function (selection)
    {
    selection.startLeft=null;
    selection.startTop=null;
    selection.viewer_startScrollLeft=null;
    selection.viewer_startScrollTop=null;
    selection.viewerIndex=this.selections.length;
    this.selections.push(selection);
    }

 galleryViewer.prototype.removeSelection=function (viewerIndex)
    {
    var selections=this.selections, l=selections.length, i;
    selection=selections[viewerIndex];
    delete selection.startLeft;
    delete selection.startTop;
    delete selection.viewer_startScrollLeft;
    delete selection.viewer_startScrollTop;
    delete selection.viewerIndex;

  for (i=viewerIndex+1;i<l;i++)
    selections[i].viewerIndex=i-1;  

  selections.splice(viewerIndex,1);
    }

var photoGalleryViewer= new galleryViewer(document.getElementById("panel").parentNode);

Insert the following line after line 27 theSelection = new Selection(64, 64, 64, 64);

Add

photoGalleryViewer.addSelection(theSelection);
photoGalleryViewer.drawScene=drawScene;

If you encounter any issues, feel free to reach out for assistance.

Answer 2

On a lazy afternoon, I found myself jotting down this code out of sheer boredom.

To implement this functionality, make sure to include the specified class in your code snippet. However, if you only require one viewer on the page, it's not necessary to use the class - everything can be encapsulated within a simple object. Should you need more viewers, consider the following:

function galleryViewer (html_viewer)
    {
    this.html_viewer=html_viewer;
    Object.defineProperty(html_viewer,"viewer_instance",{writeable:false,configureable:false,enumerable:false,value:this});
    this.selections = new Array ();
    html_viewer.addEventListener("mousedown",this.startScrolling);
    html_viewer.addEventListener("mouseup", this.endScrolling);
    html_viewer.addEventListener("scroll",this.setSelectionPosition);
    }

galleryViewer.prototype.startScrolling=function ()
    {
    var selections=this.viewer_instance.selections, selection;
    var l=selections.length;

    for (var i=0;i<l;i++)
        {
        selection=selections[i];
        selection.startLeft=selection.x;
        selection.startTop=selection.y;
        selection.viewer_startScrollLeft=this.scrollLeft;
        selection.viewer_startScrollTop=this.scrollTop;
        }
   }

galleryViewer.prototype.setSelectionPosition=function ()
  {
  var selections=this.viewer_instance.selections, selection;
  var l=selections.length;
  
  for (var i=0;i<l;i++)
    {
    selection=selections[i];
    selection.x=this.scrollLeft-selection.viewer_startScrollLeft+selection.startLeft;
    selection.y=this.scrollTop-selection.viewer_startScrollTop+selection.startTop;
    }

  this.viewer_instance.drawScene();
  }

 galleryViewer.prototype.endScrolling=function ()
   {
   var selections=this.viewer_instance.selections, selection;
   var l=selections.length;

   for (var i=0;i<l;i++)
     {
     selection=selections[i];
     selection.startLeft=null;
     selection.startTop=null;
     selection.viewer_startScrollLeft=null;
     selection.viewer_startScrollTop=null;
     }
   }

 galleryViewer.prototype.addSelection=function (selection)
    {
    selection.startLeft=null;
    selection.startTop=null;
    selection.viewer_startScrollLeft=null;
    selection.viewer_startScrollTop=null;
    selection.viewerIndex=this.selections.length;
    this.selections.push(selection);
    }

 galleryViewer.prototype.removeSelection=function (viewerIndex)
    {
    var selections=this.selections, l=selections.length, i;
    selection=selections[viewerIndex];
    delete selection.startLeft;
    delete selection.startTop;
    delete selection.viewer_startScrollLeft;
    delete selection.viewer_startScrollTop;
    delete selection.viewerIndex;

  for (i=viewerIndex+1;i<l;i++)
    selections[i].viewerIndex=i-1;  

  selections.splice(viewerIndex,1);
    }

var photoGalleryViewer= new galleryViewer(document.getElementById("panel").parentNode);

Insert the following line after line 27 theSelection = new Selection(64, 64, 64, 64);

Add

photoGalleryViewer.addSelection(theSelection);
photoGalleryViewer.drawScene=drawScene;

If you encounter any issues, feel free to reach out for assistance.

Answer 3

Answer №2

To properly implement image cropping, we need to discuss whether you prefer selecting a specific area within the canvas or resizing the entire imageCropper container before cropping.

// take a look here

Check out this JSFiddle link for more information.

Answer 4

To properly implement image cropping, we need to discuss whether you prefer selecting a specific area within the canvas or resizing the entire imageCropper container before cropping.

// take a look here

Check out this JSFiddle link for more information.

Canvas image zoom and crop feature ensures fixed selection area across all platforms

Answer №1

Answer №2

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