Table of Contents

This lesson covers how to manipulate object hierarchies in Nada.

Learning Objectives

  • Parenting / unparenting objects at runtime
  • Accessing objects through the hierarchy in code

Level Setup

  • Command : New Project
  • Create a new project using the {nav icon=clone, name=Empty 2D Project} template
  • Command : CreateSprite
  • Command : Add Resource
  • Create a NadaScript resource using the Component template template and name it SquareLogic
  • Select : Sprite object
  • In the Properties Window
  • Rename Sprite object to Square
  • Add Component : SquareLogic
  • Update the SquareLogic script to the following:
class SquareLogic : NadaComponent
{
  [Dependency] var Transform : Transform;
  
  [Property]
  var RotateSpeed : Real = 5.0;
  
  function Initialize(init : CogInitializer)
  {
    Zilch.Connect(this.Space, Events.LogicUpdate, this.OnLogicUpdate);
  }

  function OnLogicUpdate(event : UpdateEvent)
  {
    var vel = this.RotateSpeed * event.Dt;
    this.Transform.RotateAnglesWorld(Real3(0.0, 0.0, vel));
  }
}

HierarchiesSetup

The Square object rotates

Parenting at Runtime

Let's create an archetype that can be used later to spawn child cogs at runtime.

Now let's modify the SquareLogic component to spawn circles and parent them to the Square object

  • Update the SquareLogic script to the following:
class SquareLogic : NadaComponent
{
  [Dependency] var Transform : Transform;

  [Property]
  var RotateSpeed : Real = 5.0;
  
  [Property]
  var ArchetypeToSpawn : Archetype = Archetype.CircleArchetype;
  
  [Property]
  var SpawnLocation : Real3 = Real3(0.0, 2.0, 0.0);
  
  function Initialize(init : CogInitializer)
  {
    Zilch.Connect(this.Space, Events.LogicUpdate, this.OnLogicUpdate);
  }

  function OnLogicUpdate(event : UpdateEvent)
  {
    var vel = this.RotateSpeed * event.Dt;
    this.Transform.RotateAnglesWorld(Real3(0.0, 0.0, vel));
    
    if(Zilch.Keyboard.KeyIsPressed(Keys.Space))
    {
      var obj = this.Space.CreateAtPosition(this.ArchetypeToSpawn, this.SpawnLocation);
      obj.AttachTo(this.Owner);
    }
  }
}

HierarchiesAttach

The Space bar spawns child Circle object objects

Notice that the Circle object is attached to the Square object object as soon as it is created. That is done through invoking the AttachTo function on Cog, which takes a designated parent cog as its only parameter.

Similarly, you can call the Detach function to unparent any object from its hierarchy:

  • Add the following to the end of OnLogicUpdate function in the SquareLogic component:
if(Zilch.Keyboard.KeyIsPressed(Keys.D))
{
   this.Owner.Children.Current.Detach();
}
  • Command : PlayGame
  • Press key the Space key a few times
  • Press key the D key a few times

HierarchiesDettach

The D key detaches the child Circle object objects

NOTE: Zilch also sends the Attached and Detached events to cogs when the respective operation is performed on them. Additionally, you can connect to the ChildAttached and ChildDetached events on a parent objecct if you want to perform some logic upon acquiring or losing a child.

Traversing Hierarchies at Runtime

Within a script, you can easily access a cog's parent:

  • Add the following to the SquareLogic class:
[Property]
var Growth : Real = 1.1;
  • In the SquareLogic class
  • In the OnLogicUpdate function
  • Below the line, obj.AttachTo(this.Owner);
  • Add the following code:
obj.Parent.Transform.Scale *= this.Growth;

HierarchiesParentAccess

The Space bar now also grows the parent Square object object

You can also get a range containing all immediate children. Let's implement an addition to our previous script.

  • Add the following to OnLogicUpdate function in the SquareLogic component:
    if(Zilch.Keyboard.KeyIsPressed(Keys.Enter))
    {
      foreach(var child in this.Owner.Children)
      {
        child.Sprite.VertexColor = Colors.Red;
      }
    }
  • Command : PlayGame
  • Press key the Space key a few times
  • Press key the Enter key

HierarchiesChildren

The Enter key now turns the child Circle object objects red

Related Materials

Tutorials

Manual

Reference

Classes

Events

Commands

Development Task

  • T1189
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