src/com/replica/replicaisland/OrbitalMagnetComponent.java

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.replica.replicaisland;


public class OrbitalMagnetComponent extends GameComponent {
	private final static float DEFAULT_STRENGTH = 15.0f;

	private float mStrength;
	private Vector2 mCenter;
	private Vector2 mDelta;
	private Vector2 mRim;
	private Vector2 mVelocity;
	private float mMagnetRadius;
	private float mAreaRadius;
	
	public OrbitalMagnetComponent() {
        super();
        mCenter = new Vector2();
        mDelta = new Vector2();
        mRim = new Vector2();
        mVelocity = new Vector2();
        reset();
        setPhase(ComponentPhases.COLLISION_DETECTION.ordinal());
    }
    
    @Override
    public void reset() {
    	mCenter.zero();
    	mDelta.zero();
    	mRim.zero();
    	mVelocity.zero();
    	mStrength = DEFAULT_STRENGTH;
    	mAreaRadius = 0.0f;
    	mMagnetRadius = 0.0f;
    }

    @Override
    public void update(float timeDelta, BaseObject parent) {
        GameObjectManager manager = sSystemRegistry.gameObjectManager;
        if (manager != null) {
        	GameObject player = manager.getPlayer();
        	if (player != null) {
        		GameObject parentObject =  (GameObject)parent;
        		applyMagnetism(player, 
        				parentObject.getCenteredPositionX(), 
        				parentObject.getCenteredPositionY(),
        				timeDelta);
        	}
        }
    }
    
    private void applyMagnetism(GameObject target, float centerX, float centerY, float timeDelta) {
    	mCenter.set(centerX, centerY);
    	final float targetX = target.getCenteredPositionX();
    	final float targetY = target.getCenteredPositionY();
    	mDelta.set(targetX, targetY);
    	mDelta.subtract(mCenter);
    	
    	final float distanceFromCenter2 = mDelta.length2();
    	final float area2 = mAreaRadius * mAreaRadius;
    	if (distanceFromCenter2 < area2) {
    		mRim.set(mDelta);
    		mRim.normalize();
    		mRim.multiply(mMagnetRadius);
    		mRim.add(mCenter);
    		// rim is now the closest point on the magnet circle
    		
    		// remove gravity
    		final Vector2 targetVelocity = target.getVelocity();
    		GravityComponent gravity = target.findByClass(GravityComponent.class);
            final Vector2 gravityVector = gravity.getGravity();
            mVelocity.set(gravityVector);
            mVelocity.multiply(timeDelta);
            targetVelocity.subtract(mVelocity);
            
    		mDelta.add(targetVelocity);
    		mDelta.normalize();
    		mDelta.multiply(mMagnetRadius);
    		mDelta.add(mCenter);
    		
    		// mDelta is now the next point on the magnet circle in the direction of
    		// movement.
    		
    		mDelta.subtract(mRim);
    		mDelta.normalize();
    		// Now mDelta is the tangent to the magnet circle, pointing in the direction
    		// of movement.
    		
    		mVelocity.set(mDelta);
    		mVelocity.normalize();
    		
    		// mVelocity is now the direction to push the player
    		
			mVelocity.multiply(mStrength);
			float weight = 1.0f;
			if (distanceFromCenter2 > mMagnetRadius * mMagnetRadius) {
				float distance = (float)Math.sqrt(distanceFromCenter2);
				weight = (distance - mMagnetRadius) / (mAreaRadius - mMagnetRadius);
				weight = 1.0f - weight;
				mVelocity.multiply(weight);
			}
			final float speed = targetVelocity.length();
			targetVelocity.add(mVelocity);
			if (targetVelocity.length2() > (speed * speed)) {
				targetVelocity.normalize();
				targetVelocity.multiply(speed);
			}
	    	
    	}
    	
    }
    
    public void setup(float areaRadius, float orbitRadius) {
    	mAreaRadius = areaRadius;
    	mMagnetRadius = orbitRadius;
    }
}