Suspended Object Trap

Introduction

An example of what this tutorial will accomplish.

This tutorial explains the process of creating a trap consisting of a heavy object suspended by a dynamic rope which can then be triggered to fall with devastating effect. This is an advanced tutorial covering entity creation, parenting, I/O configuration, keyframe editing, and flag manipulation. Overall completion time is estimated at 45 minutes to 1 hour.

The Source Hammer editor does not allow a user to directly attach an object to a rope. However, there is a workaround. The basic idea involves parenting the end of a rope to a secondary entity. This secondary entity is then used in conjunction with a few physics entities that measure the movement of the secondary entity and translate its movements back to the rope. We'll also be creating a trigger that will break the rope when it gets damaged causing the previously suspended object to crash down! Sounds complicated but don't worry, it'll make sense once it's done. Let's get started!

Entity Creation

Create the following entities:

• A move_rope,
• a keyframe_rope,
• a phys_lengthconstraint,
• a env_spark,
• a prop_physics_override or a func_physbox,
• a logic_measure_movement,
• a brush with the same or as-near-as-possible dimensions of the prop_physics_override / func_physbox, tied (Ctrl+T) to a func_button entity.

Entity Placement

Place the following entities or brushes:

• Place the move_rope to where you'd like to anchor the rope.
• Place the prop_physics_override / func_physbox to where you'd like the object to hang from.
  • This tutorial will be using a prop instead of a physbox, but both can be used.
• Place the keyframe_rope to where you'd like to anchor the rope to the prop_physics_override or func_physbox.
  • Hint: Just inside the surface of the prop or brush works best.
  • Remember your physics: once in game, the center of gravity of the prop and the anchor point will interact and your prop will reach a balance point accordingly.
• Place the phys_lengthconstraint in the exact same location of the keyframe_rope and drag the lengthconstraint's small white circle to the center of the move_rope.
• Place the env_spark in the exact same location of the keyframe_rope.
• Place the logic_measure_movement off to the side for easy access.
• Place the brush in the same location as the prop_physics_override / func_physbox.

Entity Properties Configuration

Naming

Naming your entities is arbitrary - you can choose what names you want. For the purposes of this tutorial the nomenclature is:

• move_rope : dynamic01_move_rope
• keyframe_rope : dynamic01_keyframe_rope
• phys_lengthconstraint : dynamic01_phys_lengthconstraint
• env_spark : dynamic01_env_spark
• prop_physics_override / func_physbox : dynamic01_prop_physics_override
• logic_measure_movement : dynamic01_logic_measuremovement
• func_button : dynamic01_func_button

As you can see, each entity has the prefix dynamicXX, followed by a descriptive suffix. This is a useful naming system when you have several dynamic systems and need to keep them separate.

Keyvalues for Rope Workaround

Here comes the tricky part where most errors are made. Set the keyvalues of the entities like this:

Class: move_rope
Keyvalues		Comments
Name	dynamic01_move_rope	The name of the move_rope entity in this tutorial.
Next KeyFrame	dynamic01_keyframe_rope	The name of the keyframe_rope entity in this tutorial
Slack	0	No slack.

Class: keyframe_rope
Keyvalues		Comments
Name	dynamic01_keyframe_rope	The name of the keyframe_rope entity in this tutorial.
Slack	0	No slack here either.

Class: env_spark
Keyvalues		Comments
Name	dynamic01_env_spark	The name of the env_spark entity in this tutorial.
Parent	dynamic01_prop_physics_override	Tie the spark effect to the prop_physics_override entity.

Class: phys_lengthconstraint
Keyvalues		Comments
Name	dynamic01_phys_lengthconstraint	The name of the phys_lengthconstraint entity in this tutorial.
Entity1	dynamic01_prop_physics_override	Tie the lengthconstraint to the prop_physics_override entity too.

Class: logic_measure_movement
Keyvalues		Comments
Name	dynamic01_logic_measuremovement	The name of the logic_measure_movement entity in this tutorial.
Entity to Measure	dynamic01_env_spark	Tie the logic spark entity to the logic entity to measure the movement of the parented prop
Measure Reference	dynamic01_move_rope	Tie the move_rope entity to the logic entity as a measure refence
Entity to Move	dynamic01_keyframe_rope	Send along the measured movements of the env_spark relative to the move_rope
Movement Reference	dynamic01_move_rope	Tie the move_rope entity to the logic entity as a movement refence

Trap Trigger Creation

Time to change the func_button. First change its keyvalues like this:

Class: func_button
Keyvalues		Comments
Name	dynamic01_func_button	The name of the func_button entity in this tutorial.
Parent	dynamic01_prop_physics_override	Tie this entity to the prop_physics_override.
Disable Receiving Shadows	Yes
Move Direction (Pitch Yaw Roll)	0 0 0
Speed	0
Lip	0

Now change its flags like this:

	Flag
		Don't move
		Toggle
		Touch Activates
		Damage Activates
		Use Activates
		Starts locked
		Sparks

...and finally give it the following outputs:

		My output	Target entity	Target input	Parameter	Delay	Only once	Comments
		OnDamaged	dynamic05_logic_measure_movement	Disable		0.00	No
		OnDamaged	dynamic05_keyframe_rope1	Break		0.00	No
		OnDamaged	dynamic05_phys_lengthconstraint	Break		0.00	No
		OnDamaged	dynamic05_env_spark	Kill		0.00	No
		OnDamaged	dynamic05_func_button	Kill		0.00	No