Edit in JSFiddle

window.onload = function() {

    //canvas拡張
    $("canvas").attr({height:$("#wrapper").height()});
    $("canvas").attr({width:$("#wrapper").width()});

    //canvasをstageに
    var stage = new Stage($("canvas")[0]);
    
    //どう描くかを指定
    var g = new Graphics();
    g.beginFill("#888");
    
    //すべての頂点の丸み半径を10に指定
    g.drawRoundRect(-100,0,100,100,10);
    
    //頂点の丸み半径を個別に指定
    g.drawRoundRectComplex(0,-100,100,100,50,-10,50,0);
    
    //シェイプオブジェクトに渡す
    var s = new Shape(g);
    s.x = $(window).width()/2;
    s.y = $(window).height()/2;
    
    //ステージにシェイプをセット
    stage.addChild(s);
    
    //描画！
    stage.update();

}

<div id="wrapper">
<canvas></canvas>
</div>

html{
    min-height: 100%;
    overflow: auto;
    position:relative;
    z-index: 1;
}

body{
    min-height: 100%;
    margin: 0;
    padding: 0;
    overflow: auto;
    position: relative;
    z-index: 1;
}

#wrapper{
    height: auto;
    overflow: auto;
    position: fixed;
    z-index: 1;
    width: 100%;
    height:100%;
    min-height:100%;
}

canvas{
    position: fixed;
}