Described is a technology (e.g., in Windows® Presentation Foundation) by which user interface elements are reconfigured into a new configuration, with at least some of the elements transitioned from between configurations in an animated manner. To animate, elements have interim data computed therefor between the first configuration and the new configuration over a series of frames. As frames are rendered, the interim layout data provides an animation effect, which may be movement via interim coordinates, resizing via interim size data, and fading in or out via interim opacity data. The layout system may defer computationally expensive layout operations until the elements are in the second configuration. If an element's size is not at least a minimum, that element's visualization may be changed. If an element's content does not fit, a priority among pieces of the content may determine which piece or pieces will be shown.