Frame Lifecycle

This chapter connects the main systems across a single Bevy frame.

PreUpdate

• univis_picking_backend
  • converts pointer position into world space
  • evaluates SDF intersection against interactive entities
  • respects ancestor clipping through UClip
  • emits PointerHits for Bevy picking observers

Update

• widget systems update state, sync visuals, and emit messages
• scroll behavior, panel resize, and similar interaction systems run here
• text systems refresh text layout inputs

PostUpdate

Critical layout order:

1. update_layout_hierarchy
2. upward_measure_pass_cached
3. downward_solve_pass_safe

After layout:

• update_materials_optimized syncs UNode, ComputedSize, UBorder, and related data into materials

Why The Order Matters

• any Update change, such as panel resize or input state, must be reflected before the frame is rendered
• cache and invalidation run before measurement to avoid unnecessary work
• rendering depends on final ComputedSize and resolved transforms