dmail

 // http://stackoverflow.com/questions/21961839/simulation-background-size-cover-in-canvas
function drawImageProp(ctx, img, x, y, w, h, offsetX, offsetY) {
    if (arguments.length === 2) {
        x = y = 0;
        w = ctx.canvas.width;
        h = ctx.canvas.height;
    }

    // default offset is center
    offsetX = typeof offsetX === "number" ? offsetX : 0.5;