About layout calculation in 'draw' function

I see every time surface draw,it will calculate the layout again:

draw: function () {
var layout;
if (this.node) {
if (this.props.enableCSSLayout) {
layout = layoutNode(this.node);
}
DrawingUtils.drawRenderLayer(this.getContext(), this.node);
}
},

But I think only calculate the whole layout when style changed with the layout is better,for example,change the backgroundColor do not recalculate the laytout.