PVector zAxis = new PVector();

PVector up         = new PVector();

PVector objToCamera = new PVector();

PVector objectToCameraProjection                   = new PVector();

PVector lookAt = new PVector(0, 0, 1);

float angle;

public void rotateToCamera(PGraphics _buffer, PVector objectPosition, PVector cameraPosition)

{

_buffer.pushMatrix();

objectToCameraProjection.x = cameraPosition.x - objectPosition.x;

objectToCameraProjection.y = 0;

objectToCameraProjection.z = cameraPosition.z - objectPosition.z;

objectToCameraProjection.normalize();

up = lookAt.cross(objectToCameraProjection);

angle = PVector.dot(lookAt, objectToCameraProjection);

if ((angle < 0.9999f) && (angle > -0.9999f)) {

// _buffer.rotate(angle, up.x, up.y, up.z);

_buffer.rotate(parent.acos(angle) * 180 / parent.PI, up.x, up.y, up.z);

}

objToCamera.x = cameraPosition.x - objectPosition.x;

objToCamera.y = cameraPosition.y - objectPosition.y;

objToCamera.z = cameraPosition.z - objectPosition.z;

objToCamera.normalize();

angle = PVector.dot(objectToCameraProjection, objToCamera);

// parent.println(parent.acos(angle) * 180 / parent.PI);

if ((angle < 2f) && (angle > -2f)) {

if (objToCamera.y < 0) {

_buffer.rotate(parent.acos(angle) * 180 / parent.PI, 1, 0, 0);

} else {

_buffer.rotate(parent.acos(angle) * 180 / parent.PI, -1, 0, 0);

}

}

}