OneSidedTest.java

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 * Copyright (c) 2013, Daniel Murphy
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package org.jbox2d.testbed.tests;

import org.jbox2d.collision.Manifold;
import org.jbox2d.collision.shapes.CircleShape;
import org.jbox2d.collision.shapes.EdgeShape;
import org.jbox2d.collision.shapes.PolygonShape;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.BodyDef;
import org.jbox2d.dynamics.BodyType;
import org.jbox2d.dynamics.Fixture;
import org.jbox2d.dynamics.contacts.Contact;
import org.jbox2d.testbed.framework.TestbedTest;

public class OneSidedTest extends TestbedTest {
  private static final long PLATFORM_TAG = 10;
  private static final long CHARACTER_TAG = 11;

  enum State {
    e_unknown, e_above, e_below,
  };

  float m_radius, m_top, m_bottom;
  State m_state;
  Fixture m_platform;
  Fixture m_character;

  @Override
  public Long getTag(Fixture fixture) {
    if (fixture == m_platform)
      return PLATFORM_TAG;
    if (fixture == m_character)
      return CHARACTER_TAG;
    return super.getTag(fixture);
  }

  @Override
  public void processFixture(Fixture fixture, Long tag) {
    if (tag == PLATFORM_TAG) {
      m_platform = fixture;
    } else if (tag == CHARACTER_TAG) {
      m_character = fixture;
    } else {
      super.processFixture(fixture, tag);
    }
  }
  
  @Override
  public boolean isSaveLoadEnabled() {
    return true;
  }

  @Override
  public String getTestName() {
    return "One Sided";
  }

  @Override
  public void initTest(boolean deserialized) {
    m_state = State.e_unknown;
    if (deserialized) {
      return;
    }
    // Ground
    {
      BodyDef bd = new BodyDef();
      Body ground = getWorld().createBody(bd);

      EdgeShape shape = new EdgeShape();
      shape.set(new Vec2(-20.0f, 0.0f), new Vec2(20.0f, 0.0f));
      ground.createFixture(shape, 0.0f);
    }

    // Platform
    {
      BodyDef bd = new BodyDef();
      bd.position.set(0.0f, 10.0f);
      Body body = getWorld().createBody(bd);

      PolygonShape shape = new PolygonShape();
      shape.setAsBox(3.0f, 0.5f);
      m_platform = body.createFixture(shape, 0.0f);

      m_bottom = 10.0f - 0.5f;
      m_top = 10.0f + 0.5f;
    }

    // Actor
    {
      BodyDef bd = new BodyDef();
      bd.type = BodyType.DYNAMIC;
      bd.position.set(0.0f, 12.0f);
      Body body = getWorld().createBody(bd);

      m_radius = 0.5f;
      CircleShape shape = new CircleShape();
      shape.m_radius = m_radius;
      m_character = body.createFixture(shape, 20.0f);

      body.setLinearVelocity(new Vec2(0.0f, -50.0f));

      m_state = State.e_unknown;
    }
  }

  @Override
  public void preSolve(Contact contact, Manifold oldManifold) {
    super.preSolve(contact, oldManifold);

    Fixture fixtureA = contact.getFixtureA();
    Fixture fixtureB = contact.getFixtureB();

    if (fixtureA != m_platform && fixtureA != m_character) {
      return;
    }

    if (fixtureB != m_character && fixtureB != m_character) {
      return;
    }

    Vec2 position = m_character.getBody().getPosition();

    if (position.y < m_top + m_radius - 3.0f * Settings.linearSlop) {
      contact.setEnabled(false);
    }
  }
}