Changing gravity on collision

I'm making a game where players can walk on walls and I have this code allowing me to change gravity

var walkSpeed = 8.0; var walkBackwardSpeed = 4.0; var sidestepSpeed = 8.0; var gravity = 10.0; var maxVelocityChange = 10.0; var inAirControl = 0.1; var canJump = true; var jumpHeight = 2.0;

// added for run (set to Fire2. Change in Project Settings / Input if different desired.) var canRun = true; var runSpeed = 14.0; // negative values here makes game unhappy var runBackwardSpeed = 6.0; // negative values here makes game unhappy // var runSpeedChange = 4.0; // negative values here makes game unhappy

var canRunSidestep = true; var runSidestepSpeed = 12.0;

// added for keyboard rotation ('Horizontal' rotates instead of translates / strafe) /var canRotate = false; var rotateSpeed = 1.0; var rotateInAir = false; / private var grounded = false; private var groundVelocity : Vector3; private var capsule : CapsuleCollider; private var gravityDirection = Vector3(0,-1,0);

@script RequireComponent(Rigidbody, CapsuleCollider)

function Awake () { rigidbody.freezeRotation = true; rigidbody.useGravity = false; capsule = GetComponent(CapsuleCollider); }

function FixedUpdate () { if (grounded) { // Calculate how fast we should rotate // var rotation = Input.GetAxis("Horizontal") * rotateSpeed;

     // Set 'Horizontal' input based on rotate variable
     /*var targetVelocity = (canRotate) ? new Vector3(0, rotation, Input.GetAxis("Vertical")) 
     : new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));*/
     
     // Calculate how fast we should be moving

     targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));

     targetVelocity = transform.TransformDirection(targetVelocity);
     if (Input.GetAxis("Vertical") > 0)
     {
         targetVelocity.x *= (canRun && Input.GetButton("Fire2")) ? runSpeed : walkSpeed;
     }
     else 
     { 
         targetVelocity.x *= (canRun && Input.GetButton("Fire2")) ? runBackwardSpeed : walkBackwardSpeed;
     }

     targetVelocity.z *= (canRunSidestep && Input.GetButton("Fire2")) ? runSidestepSpeed : sidestepSpeed;
     
     
     // Rotate if rotate is enabled
     /*if (canRotate)
     {
         transform.Rotate(0, rotation, 0);
     }
     */
     
     // Apply a force that attempts to reach our target velocity
     var velocity = rigidbody.velocity;
     var velocityChange = (targetVelocity - velocity) + groundVelocity;
     velocityChange.x = Mathf.Clamp(velocityChange.x, -maxVelocityChange, maxVelocityChange);
     velocityChange.z = Mathf.Clamp(velocityChange.z, -maxVelocityChange, maxVelocityChange);
     velocityChange.y = 0;
     rigidbody.AddForce(velocityChange, ForceMode.VelocityChange);
    
     // Jump
     if (canJump && Input.GetButton("Jump"))
     {
         //rigidbody.velocity = Vector3(velocity.x, CalculateJumpVerticalSpeed(), velocity.z);
     
         rigidbody.velocity = -gravityDirection * CalculateJumpVerticalSpeed();
     
     }
    
     grounded = false;
 }
 
 else
 {
     // Add in air
     
     // Calculate how fast we should rotate
     /*rotation = Input.GetAxis("Horizontal") * rotateSpeed;
     
     // Set 'Horizontal' input behavior based on whether we can rotate in air
     targetVelocity = (rotateInAir) ? new Vector3(0, rotation, Input.GetAxis("Vertical"))
     : new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
     */    
     targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));

     targetVelocity = transform.TransformDirection(targetVelocity) * inAirControl;
     
     // Rotate if rotate in air is enabled.
     /*if (rotateInAir)
     {
         transform.Rotate(0, rotation, 0);
     }
     */
     rigidbody.AddForce(targetVelocity, ForceMode.VelocityChange);
 }
 
     
 rigidbody.AddForce(gravityDirection * gravity * rigidbody.mass);
 

}

function TrackGrounded (col : Collision) { var minimumHeight = capsule.bounds.min.y + capsule.radius; for (var c : ContactPoint in col.contacts) { if (c.point.y < minimumHeight) { //we track velocity for rigidbodies we're standing on if (col.rigidbody) groundVelocity = col.rigidbody.velocity; //and become children of non-rigidbody colliders else transform.parent = col.transform; grounded = true;

 if (col.tag == "XZdown")
     gravityDirection = Vector3(0,-1,0);
 else if (col.tag == "XYback")
     gravityDirection = Vector3(0,0,-1);
 else if (col.tag == "YZleft")
     gravityDirection = Vector3(-1,0,0);
 else if (col.tag == "XZup")
     gravityDirection = Vector3(0,1,0);
      
   }

}
}

//unparent if we are no longer standing on our parent function OnCollisionExit (col : Collision) { if (col.transform == transform.parent) transform.parent = null; }

function OnCollisionStay (col : Collision) { TrackGrounded (col); }

function OnCollisionEnter (col : Collision) { TrackGrounded (col);

}

function CalculateJumpVerticalSpeed () { // From the jump height and gravity we deduce the upwards speed // for the character to reach at the apex. return Mathf.Sqrt(2 jumpHeight gravity); }

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I copied the code from 125here125 and tweaked it a bit but I can't figure out how to make it so that when a player collides with an object with the tag XZup, for example, to make the gravity pull that character upwards.