In this recipe, we will create a very common gameplay mechanism: a moving platform. We will use a Rigid body for our character and an animated, kinematic Rigid body for the platform.
Getting ready
Before we start, you should have a scene with your character and a platform you want to animate. You can use the example project; go to the Chapter 02 Working with the animation view\Recipe 03 Animating objects world position - creating a moving platform directory. There is a scene called Example.unity there. If you open it, you will find a Sheep character in the Hierarchy. This is our character, using the Rigidbody component and a Simple Move script to move. There is also a Moving Platform game object in the Hierarchy. This is the kinematic rigid body with a Platform script attached to it. It also has an Animator component and an Animator Controller with just one animation in it.
This animation makes the platform move.
How to do it…
To create and assign an animated moving platform, follow these steps:
Select your platform game object in the Hierarchy.
1.
Open the Animation View.
2.
Make sure the record button is pressed (in the upper-left corner of the Animation 3. View).
Move the platform to the desired position in the first frame.
4.
Adjust the timeline a few seconds forward and move your platform to new 5. destination.
To make the animation loop, select the first key frame and press Ctrl + C (cmd + C 6. on Mac). Then adjust the timeline forward from the second key frame, the same
amount of seconds like the previous step. If the first key frame is on the 0 seconds mark and the second on the 10 seconds mark, set the timeline to 20 seconds mark.
Press Ctrl + V to paste the copied key frame. In our example, the platform is going from one floating island to another and back. It also has some pauses on each end to make it easier for the player to jump on to it.
When you are happy with your animation, exit the Animation View.
7.
An Animator Controller will be created and an Animation Clip will be assigned 8. to it automatically. Also, an Animator component will be added to the platform
game object.
Find the Animator Controller on the platform game object and set the Update 9. Mode property to Animate Physics. Set the Culling Mode to Always Animate.
Add a Rigidbody component to the platform and select the Kinematic checkbox.
10.
Add a collider component (a Mesh Collider or a Box Collider) to your platform.
11. If you are using a Mesh Collider, make sure to select the Convex checkbox.
Create a new script, and name the file Platform.cs.
12.
Open the script and write the following code:
13. component attached.The Collision collisionInfo object
parameter stores the information about the collision and the object we are colliding with.*/
void OnCollisionEnter(Collision collisionInfo) {
slide from it.*/
collisionInfo.transform.parent = transform;
} }
/*This function is called by Unity every time this object stop colliding with any object with a Collider component attached.
The CollisionInfo collision info parameter stores the same information as in the OnCollisionEnter function.*/
void OnCollisionExit(Collision collisionInfo) { colliding with to null. The object has no parent
at all and stops moving with the platform*/
collisionInfo.transform.parent = null;
} } }
Attach the script to the platform game object and play the game to see the effect.
14.
This moving platform will work with characters using Rigidbody components to 15. move. You can import the ThirdPersonCharacter prefab from
Unity's Standard Assets. You can also write your own simple character movement. To do so, see the There's more section.
How it works…
This is the most simple but working moving platform solution. It uses a few key elements:
Animation-driven movement: The platform is moved only by the Animation Clip created with the Animation View. This allows you to experiment with the movement easily.
Kinematic Rigid body: To animate a game object with a Rigidbody component attached, you need to set the Kinematic checkbox to true. It completely disables the physics of the Rigid Body. You can still animate the object with Kinematic set to false, but physics will still have an impact on the movement (the object will not be able to penetrate other objects, it will rotate on collisions, and so on).
Animate Physics option: Set in the Update Mode parameter of the Rigidbody component. This option makes the Rigid body to be animated in the physics loop (you can think of it as the FixedUpdate() function equivalent). It prevents the Rigid Bodies colliding with this object to jitter and behave in strange ways.
Animation in world space: Our platform is animated in world coordinates. This means that the animation sets the object's position regarding the scene's 0x, 0y, 0z point. It does not matter where the object is placed in the scene; after playing the animation, it will be placed in the positions stored in the animation's key frames.
We will discuss local space animation in the Animating object's local position – creating automatic doors recipe.
Moving platform as a parent to the character: We are setting the platform as the parent to the in-game character, which collides with it. Rigid bodies parented to other Transforms try to move with them in game. This is the easiest and rather bulletproof way of making our character move with/relative to the platform game object. And because the platform moves with the Update Mode set to Animate Physics, no jittering will occur. Instead of parenting the character to the platform, you could also experiment with creating a physical material with appropriate friction, or write your own custom solution that would add the platform's speed to the character's speed.
There's more…
In the provided example, we created our own script for moving the character using a Rigidbody component. You can find the script in the Shared scripts directory. It is called SimpleMove.cs. To make your character move:
Add a collider component (we use a Sphere Collider in the example) and 1. a Rigidbody component to it.
Create a zero friction Physics Material and assign it to the collider 2. component.
Set the Rigidbody component Constraints to Freeze Rotation in the X, Y, and Z 3. axes.
Create an empty game object, position it around 0.2 units above the character's 4. feet, and parent it to the character. Name it GroundCheck for clarity.
Attach the script to the character's game object. Attach the GroundCheck game 5. object to the Ground Check Transform field of the Simple Move script
component.
If you want your character to have an animation, create an Animator Controller 6. with float Speed, bool Ground, and Trigger Jump parameters.
Prepare idle, walk, and jump animations. Idle and walk should be looped, jump should end in the air.
Create a transition between idle and run using the Speed parameter with 7. the Speed > 0.1 condition.
Create a transition between run and idle using the Speed parameter with 8. the Speed < 0.1 condition.
Create transitions from run and idle to jump using the Jump trigger parameter.
9.
Create transitions from jump to run and idle using the Ground and Speed 10. parameters. Conditions should check if Ground is true and if Speed < 0.1
(transition to idle) or Speed > 0.1 (transition to run).
Attach the Animator Controller to your character.
11.
Parent the game camera to your character or use the provided CameraFollow.cs 12. script found in the Shared scripts directory. You can also use one of the camera
scripts found in Unity's Standard Assets.