Box2d多个夹具和定位 [英] Box2d multiple fixtures and positioning

问题描述

我试图在Box2d（在Cocos2d中）通过连接3个矩形来创建一个U形：像这样：| _ |

I'm attempting to create a "U" shape in Box2d (in Cocos2d) by joining 3 rectangles like so: |_|

不是正确的解决方案在这里，因为我不想要任何运动，所以我已经创建了一个主体是中间位和两个夹具的两侧。我把两边添加到中间位，像这样：

It sounds like joints are not the correct solution here since I don't want any movement so I have created a main body which is the middle bit and 2 fixtures for the sides. I've added the two sides to the middle bit like this:

mainBody->CreateFixture(&leftFixtureDef);
mainBody->CreateFixture(&rightFixtureDef);

这样工作，但是两个装置都被添加到mainBody的中心。我似乎无法解决如何相对于主体定位夹具。

This works, however both side fixtures get added to the center of the mainBody. I can't seem to work out how to position the fixtures relative to the main body. Attaching a sprite/node to the fixture and changing the position doesn't seem to make a difference.

任何想法？

非常感谢。

推荐答案

这是形状的属性。我没有为b2CircleShape找到这样的属性，但对于 b2PolygonShape 有 m_centroid paramter - 它是相对于身体。指定它有一个形状的有效位置。

it's the property of a shape. I did not find such property for b2CircleShape, but for b2PolygonShape has m_centroid paramter - it's the shape center coordinates relative to the body. Specify it to have a valid position of a shape.

对于b2PolyganShape有一个方法 setAsBox（w，h）但是alos有更复杂的：

For b2PolyganShape there is a method setAsBox(w, h) but alos there is more complex one:

setAsBox(float32 width, float32 height, const b2Vec2 &center, float32 rotation)

使用此方法或指定质心手动。

Use this method or specify the centroid manualy.

这里是U形的代码

b2BodyDef bDef;
bDef.type = b2_dynamicBody;
bDef.position = b2Vec2(0, 0);
b2Body *body = world_->CreateBody(&bDef);

b2PolygonShape shape;
const float32 density = 10;

shape.SetAsBox(1, 0.1);
body->CreateFixture(&shape, density);

shape.SetAsBox(0.1, 1, b2Vec2(-1 + 0.1, 1), 0);
body->CreateFixture(&shape, density);

shape.SetAsBox(0.1, 1, b2Vec2(1 - 0.1, 1), 0);
body->CreateFixture(&shape, density);

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