javascript - drag image after dropping it in canvas element -


to perform drag & drop functionality, canvas element, have draw image in element of destination using line, 

ctx.drawimage(imgelement,dropx, dropy);

because it's drawed, found difficulty in dragging again. it's can't make move anymore

i'm working on basis of code here : http://jsfiddle.net/m1erickson/cyur7/

what modifications have make, in order drag again dropped image?

keep in mind canvas bitmap.

once images drawn on canvas cannot repositioned.

to reposition image, must clear canvas , redraw image in new position.

to move , redraw image, need save @ least basic information image:

var image1={     x:50,     y:30,     image:imageobject }

you can let user drag image around canvas listening mouse events

  • in mousedown, check if mouse on image. if yes, start drag.

  • in mousemove, add distance user dragged since last mousemove images x,y position.

  • in mouseup, stop drag.

here's example code , demo: http://jsfiddle.net/m1erickson/l3vjk/

<!doctype html> <html> <head> <link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css --> <script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script> <style>     body{ background-color: ivory; }     #canvas{border:1px solid red;} </style> <script> $(function(){      var canvas=document.getelementbyid("canvas");     var ctx=canvas.getcontext("2d");     var canvasoffset=$("#canvas").offset();     var offsetx=canvasoffset.left;     var offsety=canvasoffset.top;     var isdown=false;     var startx;     var starty;     var imgx=50;     var imgy=50;     var imgwidth,imgheight;      var img=new image();img.onload=start;img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house32x32transparent.png";      function start(){         imgwidth=img.width;         imgheight=img.height;         ctx.drawimage(img,imgx,imgy);     }      function handlemousedown(e){       e.preventdefault();       startx=parseint(e.clientx-offsetx);       starty=parseint(e.clienty-offsety);        // put mousedown stuff here       if(startx>=imgx && startx<=imgx+imgwidth && starty>=imgy && starty<=imgy+imgheight){           isdown=true;       }     }      function handlemouseup(e){       e.preventdefault();       isdown=false;     }      function handlemouseout(e){       e.preventdefault();       isdown=false;     }      function handlemousemove(e){       if(!isdown){return;}       e.preventdefault();       mousex=parseint(e.clientx-offsetx);       mousey=parseint(e.clienty-offsety);        // put mousemove stuff here       if(!isdown){return;}       imgx+=mousex-startx;       imgy+=mousey-starty;       startx=mousex;       starty=mousey;       ctx.clearrect(0,0,canvas.width,canvas.height);       ctx.drawimage(img,imgx,imgy);     }      $("#canvas").mousedown(function(e){handlemousedown(e);});     $("#canvas").mousemove(function(e){handlemousemove(e);});     $("#canvas").mouseup(function(e){handlemouseup(e);});     $("#canvas").mouseout(function(e){handlemouseout(e);});  }); // end $(function(){}); </script> </head> <body>     <canvas id="canvas" width=300 height=300></canvas> </body> </html>

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