How to make Trajectory Predictor on my ball? - unity3d

Question

hey guys , So as you can see i made a robot arm grab a slingshot's objectholder with a ball in it. My arm pulls it any direction I want it but I wanted the user to know which box is going to be shot at.

Answer 1

If you're applying an impulse force (or velocity) to your ball and there is gravity in your world, your item will follow the Projectile motion;
Here you can find details about it:
https://en.wikipedia.org/wiki/Projectile_motion

Answer 2

There are basically two main options
calculating it yourself
This is probably way better for performance especially if you want a really simple trajectory preview without accounting for any collision etc
refer to linked article. But it basically comes down to
and would need slightly rework from 2D to 3D physics, should be trivial though since the important part about the Y axis basically stays the same.
You would
Call this simulation with according supposed shoot direction and velocity
Visualize the tracked positions e.g. in a LineRenderer
Physics.Simulate
This allows you to run physics updates manually all within a single frame and actually let the Physics engine handle it all for you
This costs of course a lot of performance but you get all collisions etc accounted for automatically without getting a headache
You would
Make a snapshot of all Rigid bodies in your scene - in order to reset after the simulation
Simulate the desired amount of physics steps (XY seconds ahead) while keeping track of the simulated data
reset everything to the state tracked in step 1
use the simulated data from step 2 to visualize e.g. with a LineRenderer
This might look somewhat like e.g.
public class Prediction : MonoBehaviour
{
public LineRenderer line;
public Rigidbody tracked;
private Rigidbody[] allRigidbodies;
private void Awake()
{
allRigidbodies = FindObjectsOfType<Rigidbody>();
}
private void LateUpdate()
{
// Wherever you would get this from
Vector3 wouldApplyForce;
// Step 1 - snapshot
// For simplicity reasons for now just the positions
// using some Linq magic
var originalPositions = allRigidbodies.ToDictionary(item => item, item => item.position);
// Step 2 - Simulate e.g. 2 seconds ahead
var trackedPositions = new Vector3 [(int) (2 / Time.fixedDeltaTime)];
Physics.autoSimulation = false;
tracked.AddForce(wouldApplyForce);
for(var i = 0; i < trackedPositions.Length; i++)
{
Physics.Simulate(Time.fixedDeltaTime);
trackedPositions[i] = tracked.position;
}
// Step 3 - reset
foreach (var kvp in originalPositions)
{
kvp.Key.position = kvp.Value;
}
Physics.autoSimulate = true;
// Step 4 - Visualize
line.positionCount = trackedPositions.Length;
line.SetPositions(trackedPositions);
}
}
Of course we won't talk about performance here ^^