css - HTML canvas resize and mouse coordinates -


i'm using canvas predefined width , height, result of available resource i've render.
resources sizes not same size screen (mobile device) "stretch" document "viewport" optimal, kind of full screen , fill appearance. 1 works , application running correct (based on playn).

the problem appeared when requested open "external" pages in application using iframe. appears iframe inherits "viewport" parent document , content of website broken (zoomed in or zoomed out).

i checked solution keep "viewport=1" play css stretch canvas, application looks mouse/touch events got broken, receives real (zoomed) position application expects position based on original canvas size.

example here.

any idea how stretch canvas , still keep coordinates correct original dimension? 

<body>     <canvas id="canvas" width="100px" height="100px" style="border: 1px solid black"></canvas> </body> 
var can = document.getelementsbytagname("canvas")[0]; can.style.width = "300px"; can.style.height = "300px";  can.addeventlistener('mousemove', function(evt) {     var mousepos = getmousepos(canvas, evt);     var message = 'x: ' + mousepos.x + ', y:' + mousepos.y;     writemessage(canvas, message); }, false);  function writemessage(canvas, message) {     var context = canvas.getcontext('2d');     context.clearrect(0, 0, canvas.width, canvas.height);     context.font = '8pt calibri';     context.fillstyle = 'black';     context.filltext(message, 10, 25);   }  function getmousepos(canvas, evt) {     var rect = canvas.getboundingclientrect();     return {       x: evt.clientx - rect.left,       y: evt.clienty - rect.top     };   }


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