Scratch To Unity: Motion

This post provides a handy reference guide to go from Scratch’s “Motion” category of code blocks to C# with Unity.

Code Alternatives

Before you dive in, I wanted the opportunity to present a few alternatives for your animation needs. Unity has a lot of features you wont find in Scratch, so doing things the “Scratch way” inside of Unity may not actually be the best approach. Take a moment to learn the “Unity way” of doing things and see what works best for you.

In Unity, I may only program my motions when there is some dynamic nature involved. If I were creating a cut-scene or flying logo, or any other kind of animation that should always play out the same way, you can create those kinds of animations directly inside of the Unity interface without any code at all. Click here to watch a video tutorial by Unity.

If you want to do character animation, a lot of times animation will actually be created outside of Unity and imported in. The animation will then be controlled using an Animator component by a State Machine. Click here to learn more about that kind of setup.

Sometimes, even dynamic motion can be handled automatically. It really depends on how much control I require. In some cases, I am happy to allow Unity’s physics engine to determine where and how all of my object motion plays out. Click here to learn how Unity’s physics engine can improve and simplify your motion needs.

There are many more tutorials on animation and physics as well as a variety of topics all on Unity’s website. Click here to explore for yourself.

Code Blocks

Click on the picture of any of these Scratch code blocks to see how to write similar code statements in C#. For convenience I have created placeholder methods that show how to get a random position, and a mouse position in world space which some of the blocks may reference.



















transform.Translate(10, 0, 0);


transform.Rotate(0, 0, -15);


transform.Rotate(0, 0, 15);


transform.localPosition = RandomPosition();

See RandomPosition.


transform.localPosition = new Vector3(0, 0, 0);


void Start()
{
    var pos = RandomPosition();
    var glide = Glide(1, pos);
    StartCoroutine(glide);
}

See Glide.


void Start()
{
    var pos = new Vector3(0, 0, 0);
    var glide = Glide(1, pos);
    StartCoroutine(glide);
}


transform.localEulerAngles = new Vector3(0, 0, 90);


transform.LookAt(MousePosition());


var pos = transform.localPosition;
pos.x += 10;
transform.localPosition = pos;


var pos = transform.localPosition;
pos.x = 0;
transform.localPosition = pos;


var pos = transform.localPosition;
pos.y += 10;
transform.localPosition = pos;


[csharp]
var pos = transform.localPosition;
pos.y = 0;
transform.localPosition = pos;


void OnCollisionEnter(Collision collision)
{
    transform.forward = Vector3.Reflect(transform.forward, collision.contacts[0].normal);
}


I am not aware of anything that is a good match for this code block. The closest match I can think of is if you are allowing phyiscs to animate your game objects and add constraints so that they can only rotate on a certain axis. The code below would only rotate around the vertical axis, kind of like a globe.

var rigidBody = GetComponent<Rigidbody>();
rigidBody.constraints = RigidbodyConstraints.FreezeRotationX | RigidbodyConstraints.FreezeRotationZ;


var xPos = transform.localPosition.x;


var yPos = transform.localPosition.y;


var direction = transform.localEulerAngles.z;


This shows a sample of obtaining a random position. Unlike the stage in Scratch, the world in Unity is unbounded. I have imposed my own range of values to pick from.

Vector3 RandomPosition()
{
    var min = Vector3.zero;
    var max = new Vector3(10, 10, 10);
    return RandomPosition(min, max);
}

Vector3 RandomPosition(Vector3 min, Vector3 max)
{
    var x = Random.Range(min.x, max.x);
    var y = Random.Range(min.y, max.y);
    var z = Random.Range(min.z, max.z);
    return new Vector3(x, y, z);
}


This method shows a sample of obtaining a world position given the mouse position. Since Unity works in 3D space, we ray-cast from the screen coordinates of the mouse, to the hit location in world space. Note that you have to have an object with a collider in view of the camera for this to work.

Vector3 MousePosition()
{
    RaycastHit hit;
    Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    if (Physics.Raycast(ray, out hit))
    {
        return hit.point;
    }
    return Vector3.zero;
}


This method shows a sample of animating an object of the specified number of seconds, to the specified local position.

IEnumerator Glide(float seconds, Vector3 position)
{
    var start = transform.position;
    var time = 0f;
    while (time < seconds)
    {
        yield return null;
        time += Time.deltaTime;
        var t = Mathf.Clamp01(time / seconds);
        transform.position = Vector3.Lerp(start, position, t);
    }
}

Links

Here are a few links that are relevant to this material and can help you dive a little deeper if you need more help.

Summary

This should cover all of the code blocks in Scratch’s “Motion” category. If you have any questions about this reference guide feel free to ask below.

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