Basic Concept

The basic concept of the Nifty-GUI layout is that it processes the layout in two stages:

1. Measure
2. Arrange

The first stage is the measurement stage. During that stage the elements calculate and report the optimal size they require to display their content. This calculation happens based on the available size that is reported by the parent node. If a layout node splits it's area in two equally it will report only half of it's original size to the child nodes. This way the nodes are able to calculate their layout according to the present restrictions. This may be relevant in case nodes need to wrap their children into lines or columns and require more height.

The calculated size is treated as desired size. It is not a requirement for the layout. Most of the layout nodes are not able to arrange the children at exactly the same size as they requested.

The second stage of the layout is the arrangement stage. During this stage each nodes receives it's exact position and size relative to the root node. The default behavior for the layout is to use all space that is available to place the child nodes, regardless of their desired size. Some of the layout nodes are able to handle nodes that request a smaller surface in one dimension or in both. These layout nodes will use the desired size of their children. An example for such a layout node is the AbsoluteLayoutNode. This node is able to place child nodes freely on it's surface and layout them according to their desired size in both dimensions.