How Can I Create Two Mediums with Different Drag Properties Inside VerletPhysics2D World?

Processing Libraries
1

I am trying to modify the example Attraction2D so that the drag increases from half of the screen(world), making the particles appear to be falling into water. Is it possible to create two different mediums whose drag values can be manipulated separately. I want the top half of the screen to have a drag value of 0.05f and the bottom half of the screen 0.1f.

/**
 * <p>This example demonstrates how to use the behavior handling
 * (new since toxiclibs-0020 release) and specifically the attraction
 * behavior to create forces around the current locations of particles
 * in order to attract (or deflect) other particles nearby.</p>
 *
 * <p>Behaviors can be added and removed dynamically on both a
 * global level (for the entire physics simulation) as well as for
 * individual particles only.</p>
 * 
 * <p>Usage: Click and drag mouse to attract particles</p>
 */

/* 
 * Copyright (c) 2010 Karsten Schmidt
 * 
 * This demo & library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * http://creativecommons.org/licenses/LGPL/2.1/
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
import toxi.geom.*;
import toxi.physics2d.*;
import toxi.physics2d.behaviors.*;

int NUM_PARTICLES = 750;

VerletPhysics2D physics;
AttractionBehavior2D mouseAttractor;

Vec2D mousePos;

void setup() {
  size(680, 382,P3D);
  // setup physics with 10% drag
  physics = new VerletPhysics2D();
  physics.setDrag(0.5f);
  physics.setWorldBounds(new Rect(0, 0, width, height));
  // the NEW way to add gravity to the simulation, using behaviors
  physics.addBehavior(new GravityBehavior2D(new Vec2D(0, 0.15f)));
}

void addParticle() {
  VerletParticle2D p = new VerletParticle2D(Vec2D.randomVector().scale(5).addSelf(width / 2, 0));
  physics.addParticle(p);
  // add a negative attraction force field around the new particle
  physics.addBehavior(new AttractionBehavior2D(p, 20, -1.2f, 0.0f));
}

void draw() {
  background(255,0,0);
  noStroke();
  fill(255);
  if (physics.particles.size() < NUM_PARTICLES) {
    addParticle();
  }
  physics.update();
  for (VerletParticle2D p : physics.particles) {
    ellipse(p.x, p.y, 5, 5);
  }
}

void mousePressed() {
  mousePos = new Vec2D(mouseX, mouseY);
  // create a new positive attraction force field around the mouse position (radius=250px)
  mouseAttractor = new AttractionBehavior2D(mousePos, 250, 0.9f);
  physics.addBehavior(mouseAttractor);
}

void mouseDragged() {
  // update mouse attraction focal point
  mousePos.set(mouseX, mouseY);
}

void mouseReleased() {
  // remove the mouse attraction when button has been released
  physics.removeBehavior(mouseAttractor);
}
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