Nevermind, I got it working by creating the new createjs.Bitmap
object from an Image object instead of passing the url of the image to the Bitmap's constructor. Then adding both my drawingCanvas's createjs.Shape
object and Bitmap's object to the loaded event handler. So this works:
var image, stage, drawingCanvas, bitmap;
function init(){
image = new Image();
image.onload = handleImgLoad();
image.src = 'image-source-url.png';
stage = new createjs.Stage("testCanvas");
createjs.Touch.enable(stage);
drawingCanvas = new createjs.Shape();
}
function handleImgLoad(){
bitmap = new createjs.Bitmap(image);
stage.addChild(bitmap, drawingCanvas);
... code to handle mouseup/down/move events...
}