问题描述
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在零重力太空游戏中检测碰撞时遇到很多麻烦。希望这张图片可以帮助我解释一下：
http://i.stack.imgur.com/f7AHO.png
白色矩形是连接了b2polygonShape固定装置的静态物体，如下所示：
// Create the line physics body deFinition
b2BodyDef wallBodyDef;
wallBodyDef.position.Set(0.0f,0.0f);
// Create the line physics body in the physics world
wallBodyDef.type = b2_staticBody; // Set as a static body
m_Body = world->CreateBody(&wallBodyDef);
// Create the vertex array which will be used to make the physics shape
b2Vec2 vertices[4];
vertices[0].Set(m_Point1.x,m_Point1.y); // Point 1
vertices[1].Set(m_Point1.x + (sin(angle - 90*(float)DEG_TO_RAD)*m_Thickness),m_Point1.y - (cos(angle - 90*(float)DEG_TO_RAD)*m_Thickness)); // Point 2
vertices[2].Set(m_Point2.x + (sin(angle - 90*(float)DEG_TO_RAD)*m_Thickness),m_Point2.y - (cos(angle - 90*(float)DEG_TO_RAD)*m_Thickness)); // Point 3
vertices[3].Set(m_Point2.x,m_Point2.y); // Point 3
int32 count = 4; // Vertex count
b2polygonShape wallShape; // Create the line physics shape
wallShape.Set(vertices,count); // Set the physics shape using the vertex array above
// Define the dynamic body fixture
b2FixtureDef fixtureDef;
fixtureDef.shape = &wallShape; // Set the line shape
fixtureDef.density = 0.0f; // Set the density
fixtureDef.friction = 0.0f; // Set the friction
fixtureDef.restitution = 0.5f; // Set the restitution
// Add the shape to the body
m_Fixture = m_Body->CreateFixture(&fixtureDef);
m_Fixture->SetUserData(\"Wall\");[/code]
/*------ Check for collisions ------*/
if (m_Physics->GetWorld()->GetContactCount() > 0)
{
if (m_Physics->GetWorld()->GetContactList()->GetFixtureA()->GetUserData() == \"Player\" &&
m_Physics->GetWorld()->GetContactList()->GetFixtureB()->GetUserData() == \"Wall\")
{
m_Player->CollideWall();
}
}
解决方法
边界框是AABB（轴对齐的边界框），这意味着它将始终与笛卡尔轴对齐。 AABB通常用于广相碰撞检测，因为它是一个相对简单（且便宜）的计算。
如果要获得更准确的结果（如米卡指出，不是像素完美的），则需要确保针对对象的OBB（定向边界框）进行测试。
另外，我也同意米卡（Micah）的回答，即您很可能需要一个更通用的系统来处理碰撞。即使您只有墙壁和播放器，也无法保证哪个对象将是A，哪个对象将是B。而且，当您添加其他对象类型时，这将很快解散。
, 从文档（添加到尝试处理您的情况）开始，创建联系人侦听器并不十分困难：
class MyContactListener:public b2ContactListener
{
private:
PlayerClass *m_Player;
public:
MyContactListener(PlayerClass *player) : m_Player(player)
{ }
void BeginContact(b2Contact* contact)
{ /* handle begin event */ }
void EndContact(b2Contact* contact)
{
if (contact->GetFixtureA()->GetUserData() == m_Player
|| contact->GetFixtureB()->GetUserData() == m_Player)
{
m_Player->CollideWall();
}
}
/* we\'re not interested in these for the time being */
void PreSolve(b2Contact* contact,const b2Manifold* oldManifold)
{ /* handle pre-solve event */ }
void PostSolve(b2Contact* contact,const b2ContactImpulse* impulse)
{ /* handle post-solve event */ }
};
m_Physics->GetWorld()->SetContactListener(new MyContactListener(m_Player));