Unity 2019 3D Game Physics

What is the Collider2D component and which of its properties are most important for us to use?

   •  The Collider2D component defines the shape of an object for the purposes of physical collisions

   •  Circle Collider2D and Box Collider2D are among the most popular types

   •  IsTrigger is an important property which determines if the collider is solid or not

What are 2D Effectors and why are they useful?

   •  The 2D Effector component directs the forces of physics when colliders make contact

   •  2D Effectors give fine control over friction and other forces

   •  2D Effectors can be used for explosions, conveyor belts, platforms, and more

What are 2D joints and why are they useful?

   •  The Joint2D component maintains a positional relationship with one or more GameObjects

   •  The HingeJoint2D is useful to create doors, bridges, and more

   •  2D joints are useful to mimic real-world objects or to add unique gameplay

What is unique about the Sprite Shape and how does it relate to physics?

   •  Sprite Shape gives the freedom to create rich free-form, organic 2D environments, straight in Unity

   •  The Sprite Shape is a preview feature in Beta and requires simple, additional installation

   •  Sprite Shapes generate appealing visuals, as well as, colliders for full physics simulation

What is the physics material asset, how, and when do we use it?

   •  The physics material asset describes how to handle colliding objects (friction and bounciness)

   •  It is optional and may be added to the Rigidbody, in both 2D and 3D

   •  Use it when your game physics needs custom friction and bounciness

What are 3D joints and why are they useful?

   •  The 3D Joint component maintains a positional relationship with one or more GameObjects

   •  The HingeJoint3D is useful to create chains

   •  3D Joints are useful to mimic real-world objects or to add unique gameplay

What is Ragdoll physics and how do we use it?

• Ragdoll physics is realistic physics movement of an unconscious humanoid character model

• It is useful for showing the reaction to a character being killed or knocked unconscious

• Use the Unity ragdoll wizard window to set up a new character model

What is Unity Terrain and how do we create Unity Terrain with physics support?

   •  The realistic physics interaction between the organic earth surface and other GameObjects is called Terrain physics

   •  Create a new Terrain through the Unity Menu: GameObject -> 3D Object -> Terrain

   •  Terrain physics is supported automatically via the Terrain Collider component

What are the 3 OnCollision events, and why are they useful?

   •  OnCollisionEnter and OnCollisionExit happen at the start and end of the collision, whereas, OnCollisionStay repeats during the collision

   •  OnCollision events are useful to detect collisions between Rigidbodies

   •  The Collision.gameObject property can be checked to know what did one hit

What are the 3 OnTrigger events, and why are they useful?

   •  OnTriggerEnter and OnTriggerExit happen at the start and end of the intersection, whereas, OnTriggerStay repeats during the intersection

   •  OnTrigger events are useful to detect intersections between colliders

   •  The Collider.gameObject property can be checked to know what did one hit

What is the difference between traditional movement and physics-based movement, and how are physics forces added?

   •  Traditional movement occurs on update with the transform component. Physics movement occurs during FixedUpdate with the Rigidbody component

   •  The most common way to add physics force is with the Rigidbody.AddForce () method

   •  Using the ForceMode of force is most common for gradual movement which respects mass

What are ways to manipulate physics properties and what are common use cases?

• Many physics properties can be set in both the Unity Inspector and with C# code

• A common use of isKinematic and useGravity is to toggle on and off physics for a specific GameObject

• A common use of IsSleeping is to check if a GameObject has come to rest

What are spatial queries and why are they useful in gaming?

   •  Spatial queries project a Ray (line) or a Collider (shape) through space to judge distances and potential future collisions

   •  A common use case for raycasting is to detect what could be in front of your GameObject

   •  A common use case of RaycastCommand is to run many raycast operations async and in parallel to improve game performance

Why is physics debugging important and what are the tools available?

   •  Physics is highly complex and resource intensive, so optimization is important to improve game performance

   •  Debug.DrawRay() is useful to visualize certain operations in the editor and to quality-assure the project

   •  The Physics Debugger and Profiler window are useful to inspect the performance impact of physics solutions with an eye toward improvement

How do we proceed from initial inspiration to planning a game project?

   •  First, use the inspiration for reference and pick the parts we want to use

   •  Next, breakdown the project into major tasks

   •  Lastly, we completely open Unity, and set up the project structure and scene hierarchy

How do we take user input and create projectile motion?

   •  First, use the mouse input from the user to aim

   •  Next, use Rigidbody.AddForce() to create projectile motion

   •  Lastly, isolate key gameplay variables for easy tweaking

How do we create a flexible system of various game obstacles?

   •  First, create a WorldItem concept with OnCollision events and health

   •  Next, send out damage events and use that to update graphics

   •  Lastly, tweak the resistance to damage to give a good difficulty level

How do we decide when the game end, for example, win and loss?

   •  First, decide the rules of the game

   •  Next, implement those rules in code using gaming paradigms like score and lives

   •  Lastly, create a UI (text/images) to communicate the rules and the result (win and loss)

What is polish and how do we add it to please the users?

   •  Polish is the input, animation, and graphics used to make a good game great

   •  Identify the aspects of our game that need polish

   •  Add easy-to-implement fades and tweens to please the eye

How do we proceed from initial inspiration to planning a game project?

   •  First, use the inspiration for reference and pick the parts you want to use

   •  Next breakdown the project into major tasks

   •  Lastly, open Unity and set up the project structure and scene hierarchy

How do we take user input and create physics motion?

   •  First, use the keyboard input from the user

   •  Next, use Rigidbody.AddForce() to create physics motion

   •  Lastly, isolate key gameplay variables for easy tweaking

How do we create a flexible system of various game obstacles?

   •  First, plan for the types of objects in the world and decide on behavior

   •  Next, create movable and immovable objects

   •  Lastly, do the level design to create a fun and challenge

How do we decide when the game ends? for example (win and loss)

   •  First, decide on the rules of the game

   •  Next, implement those rules in code using gaming paradigms like score and time

   •  Lastly, create a UI (text/images) to communicate the rules and the result (win and loss)

What is polish and how do we add it to please the users?

   •  Polish is the input level design and input, used to make a good game great

   •  Identify aspects of our game that need polish

   •  Add easy-to-implement fades and tweens to please the eye

What the, best practices for physics projects to help ease development and scale your projects?

   •  Use only 2D physics for 2D games and only 3D physics for 3D games

   •  Use physics as it was intended, including moving via physics forces

   •  Be aware of which operations are processor intensive and avoid them

How do you get the best performance in your physics projects?

   •  Use the latest version of Unity for the best performance

   •  Adjust physics settings like Time.fixedDeltaTime and Physics.sleepThreshold to optimize performance

   •  Use primitive colliders instead of mesh colliders for efficient runtime playback

How can you predict the path of a Rigidbody?

   •  When prediction is needed, include it early in development, for best results

   •  Move your object with physics forces

   •  Use the separate UnityEngine.PhysicsScene to run the predictive calculations

What is Unity DOTS and how will it impact the future of Unity physics?

   •  The Data-Oriented Technology Stack (DOTS) offers high performance by default

   •  DOTS features include the C# Job System, the (ECS) pattern for writing code, and the burst compiler for optimization

   •  The future of Unity Physics with DOTS represents blazing fast speed improvements