ZLayout

ZLayout is a layout paradigm that adds an explicit depth axis to two-dimensional user interfaces, enabling developers to reason about stacking and occlusion in three dimensions. While traditional layouts arrange elements in a plane, ZLayout models a z-dimension that determines which components appear in front of others when they overlap. It is applicable to web, desktop, and mobile UI toolkits and is commonly used to manage layered components such as modal dialogs, drawers, popovers, and card stacks.

Core concepts in ZLayout include depth values, stacking contexts, and constraints that relate depth to position and size. Elements can hold fixed depth or allow the system to assign depths based on state, focus, interaction, or animation. Grouping mechanisms enable a set of elements to share a base depth, while transitions provide smooth depth changes to reflect state changes without altering 2D layout constraints.

In practice, a ZLayout system assigns a z-value to each element, resolves a final draw order from depth information and containment rules, and integrates with the existing 2D layout model to preserve spatial relationships. It supports depth-aware animations, accessibility considerations for focus management when layers change, and careful handling of rendering performance in complex interfaces.

Origins for the term ZLayout appear in UI design discussions and framework documentation as a way to describe layering strategies. There is no single universal standard for ZLayout, and implementations vary in naming and detail across different libraries and platforms. Related concepts include z-index and stacking contexts, 3D transforms, and overlay or modal management in graphical user interfaces.