How can I set hyperbolic path?

Development Programming & Scripting AI
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1

I have a tower which should shoot arrows on enemys.
I have the start location of the arrow and I have the enemy location.
How can I set a path for the arrow?

(The game is 3D)

2

Maybe you can use curve:

What mouvement do you want ?

Is your ennemi is in mouvement ?

Is your arrow has a constant time to travel ?

3

I do not see how I curve will help me.
-What do you mean by whay movement do I want?
-The enemy position can be dynamic but it does not matters to the arrow. It needs to reach to static point that sets at run time.
-No.

4

If you have physic enable your arrow you juste have to set an impulse to your arrow at start, then let gravity do the rest.

5

Yes, but I have a tagert to be reached. Which means that I need the calculate the specific initial speed of the arrow. I do not know how to do that.

6

Ok, i can’t help you on that. sorry. You will need value as friction and mass of your arrow. I m not good enough in mecanic. If i was you i would use something easier: disable physic and use SetActorLocation (), that is why you can use Curve.

7

Hey Darkstorm,

Turns out ol’ Isaac “Apples Hurt” Newton can help you here. One of Newton’s kinetic equations is:

D = Vi * t + 1/2 * A * t * t

You know the distance (you have a start and end point), you know the time (assuming it’s constant), and you know the acceleration (gravity and some forward speed). Given all that, we can re-arrange this equation to get Vi.

Vi = (D - (0.5 * A * t * t)) / t

So, let’s start filling in some of those parameters.

// Let's just assume we have a "Launcher" actor which is where our arrow spawns from, and a "Target" which is just some 3D point in space.
const float arrowSpeed = 1.0f; // This is just some constant for our arrow acceleration. Since arrows don't have motors, just set this to 1.0f.
const float flightTime = 1.0f; // Reach our target in 1 second.
const FVector& arrowStart = Launcher->getActorLocation();
const FVector& arrowEnd = Target;
const FVector distanceVec = arrowEnd - arrowStart;

// Construct our acceleration. This assumes there's no Pitch/Roll to the "Launcher" actor.
const FVector& arrowDirection = Launcher->getActorRotation().Vector().SafeNormal();
const float gravity = GetWorld()->GetGravityZ();
const FVector acceleration(arrowDirection.X * arrowSpeed, arrowDirection.Y * arrowSpeed, gravity);

// Solve for Velocity
const FVector velocityInitial = (distanceVec - (0.5f * acceleration * flightTime * flightTime)) / flightTime;

// Apply the velocity to your arrow and away it goes!

I don’t have a sandbox setup to test this, but I’ve written similar code and this approach has worked well for me in the past - hopefully it’s what you’re looking for. Otherwise a quick google of “Projectile Motion” can give you numerous approaches and walkthroughs depending on the behavior you are looking for.

Good luck!

8

Thank you it works!

I have just needed to add: velocityInitial.Z = 0;