1. A computer implemented method comprising: receiving, by a development tool, input laying out a plurality of user interface items and defining a first constraint image, the first constraint image graphically establishing size information of the plurality of user interface window items with respect to a first window size; receiving, by the development tool, input laying out the plurality of user interface items and defining a second constraint image, the second constraint image graphically establishing size information of said plurality of user interface window items with respect to a second window size; capturing, by the development tool, a resizing constraint from at least one of the first constraint image and the second constraint image; and generating, by the development tool, program code for dynamically generating a user interface windows of various sizes different than said first window size and said second window size and having said plurality of user interface window items disposed therein, wherein the code is generated using the captured resizing constraint and wherein a size of each of said plurality of user interface window items within said dynamically generated user interface windows is determined as a function of said size information of said first and second constraint images.