Resizing photo on a canvas without losing the aspect ratio

Question

Hi all thanks for any help in advance. I am writing a phonegap app and can not get the photo to shrink without either losing the aspect or cropping the image by mistake. In the function below "imageData" is a 64bit string of the photo that the camera took. I can draw the image onto the canvas on my page, but if the picture was taken in landscape then it is smashed together. If i do not scale it either by using the scale function or the drawimage function then i get only the top corner of the photo. A example: i took a photo the image width in the onPhotoDataSuccess function shows it to be 1296px wide, and 968px height. But my canvas on the iPhone is 272px wide (portrait mode). I have tried many different scaling methods on the web and this appears to be the closest by not quite. What am i doing wrong?

 function onPhotoDataSuccess(imageData) 
{
var myImage = new Image();
var thecanvas = document.getElementById("queImg");
var ctx = thecanvas.getContext("2d"); 
myImage.onload = function() 
  { 
    thecanvas.setAttribute('width', '100%');
    thecanvas.setAttribute('height', 'auto');
    ctx.scale((myImage.width * 0.15), (myImage.height * 0.15));  
    ctx.drawImage(myImage, 0, 0);   
    }     

    myImage.src = "data:image/jpeg;base64," + imageData;      
}

Answer 1

Scaling is built in to drawImage.

Don't use setAttribute when dealing with canvas, call canvas.width = 272 instead, and only with whole pixel values.

Here is some working code to get you started:

 function onPhotoDataSuccess(imageData)
{
var myImage = new Image();
var thecanvas = document.getElementById("queImg");
var ctx = thecanvas.getContext("2d");

    myImage.onload = function() {
    ctx.drawImage(myImage, 0, 0, myImage.width * 0.15, myImage.height * 0.15);
    }     

    myImage.src = "http://placekitten.com/1296/968";
}


onPhotoDataSuccess(null);

Live example:

http://jsfiddle.net/QBTrg/6/