断言失败：面积 > 1.19209

Question

当我运行我的程序使用 Box2D 时，我遇到了这个奇怪的错误，这真的出乎意料，因为它在一个与我的项目无关的文件中（未构建的文件夹未链接到我的项目）。我为 VS12 获得了 Box2D 的副本，并为我的项目构建了它，并按照此处的教程设置项目：https://www.youtube.com/watch?v=kEClRFKyGkw&list=PLSPw4ASQYyymu3PfG9gxywSPghnSMiOAW&index=53

这是我的代码：

void Box::init(b2World* world, const glm::vec2& position, const glm::vec2& dimensions)
{
    m_dimensions = dimensions;
    b2BodyDef boxDef;
    boxDef.type = b2_dynamicBody;
    boxDef.position.Set(position.x, position.y);
    m_body = world->CreateBody(&boxDef);
    b2PolygonShape boxShape;
    boxShape.SetAsBox(position.x / 2.0f, position.y / 2.0f);

    b2FixtureDef fixtureDef;
    fixtureDef.shape = &boxShape;
    fixtureDef.density = 1.0f;
    fixtureDef.friction = 0.3f;

    m_fixture = m_body->CreateFixture(&fixtureDef);
}

我在哪里调用 init():

    b2Vec2 gravity(0.0f, -9.8f);
    m_world = std::make_unique<b2World>(gravity);
    b2BodyDef groundBodyDef;
    groundBodyDef.position.Set(0.0f, -10.0f);
    b2Body* groundBody = m_world->CreateBody(&groundBodyDef);
    b2PolygonShape groundShape;
    groundShape.SetAsBox(50.0f, 10.0f);
    groundBody->CreateFixture(&groundShape, 0.0f);
    Box newBox;
    newBox.init(m_world.get(), glm::vec2(0.0f, 14.0f), glm::vec2(15.0f, 15.0f));
    m_boxes.push_back(newBox);

A window 弹出如下：

我的控制台上打印的错误：

Assertion failed : area > 1.19209 2896e-07F, path_to_unbuild_box2d\box2d_v2.3.0\box2d\box2d\collision\shapes\b2 polygonshape.cpp, line 422

这是错误发生的地方（当我点击 Retry 时）line 336 b2Fixture.h:

inline void b2Fixture::GetMassData(b2MassData* massData) const
{
    m_shape->ComputeMass(massData, m_density);
}

问题 1 已解决

boxShape.SetAsBox(dimensions.x / 2.0f, dimensions.y / 2.0f); ///Instead of position.

Answer 1

The line of code that's failing is（如 "Assertion failed" 消息中所述）：

b2Assert(area > b2_epsilon);

说明你的多边形很小（看断言，面积小于1.192092896e-07F，也就是值0.0000001192092896，很小）。

可能 boxShape 的大小无效。在行上设置断点：

boxShape.SetAsBox(position.x / 2.0f, position.y / 2.0f);

并检查 position 的值。确保将框的尺寸设置为合理的值。我敢打赌你不是。

断言失败：面积 > 1.19209

Assertion failed : area > 1.19209

c++

box2d