For Space Duel, I wanted to make a black hole… one that would bend the trajectory of the shots in the game and attract or swallow the player’s spaceship.

This is what I created to make a simple arcade-style gravity well.

I did some digging around (and with some help from NCarter on the IRC Channel*, iirc), I came up with this little piece of code that went into the “Update” function of the moving objects, or object controller if there was a controller responsible for a collection of objects like shots:

Transform thisTransform;
GameObject blackHole;
float gravityRadius;
float gravityConstant;

if (blackHole.active) {
      Vector3 gravityVector = blackHole.transform.position - thisTransform.position;
      float gravityDistance = 
            Vector3.Distance(blackHole.transform.position, thisTransform.position);
      Vector3 gravityStrength = Vector3.zero;
      gravityStrength.x = gravityConstant / Mathf.Pow(gravityDistance, 2);
      gravityStrength.z = gravityConstant / Mathf.Pow(gravityDistance, 2);
      if (gravityDistance < gravityRadius) {
            currentVelocity = 
                  currentVelocity + (Vector3.Scale(gravityStrength, gravityVector));
      }
}

I have also put this code up on pastebin.

This was implemented in a very simple manner.

Each object is aware of the black hole, rather than the black hole acting on each object.

thisTransform is set in Awake or Start and is a reference to the object’s own transform which is cached for performance purposes.

The GameObject blackHole is a reference to the black hole, so we can find the distance between and angle to the black hole from the object. This can be found or referenced in a number of different ways.

gravityRadius limits how far we want the black hole to effect objects. This was implemented in an arcade style game, so I needed this control over the radius, rather than just making a mass and letting it affect things naturally.

Lastly, gravityConstant is how strong the black hole is. A name such as “mass” would also work. I chose this name for the variable, as the actual gravityStrength – or how much pull is being exerted on the object – is dependent on the distance between the object and the black hole. This can be seen in the code as: Vector3 gravityStrength = Vector3.zero; which is then calculated per frame per object.

I’ve had a few people ask for this code, or code to make a gravity well of some sort, so I hope this helps!

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