无法在 iPhone 上的 Box2D 中设置“setAsEdge”

Question

这段代码将在 iPhone 屏幕周围创建线条，但底线应该在中间（我需要更改 .y 但我不知道如何更改）。 该怎么做？

有人可以向我解释这些“setAsEdge”方法吗？

// Define the ground body.
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0,0); // bottom-left corner

// Call the body factory which allocates memory for the ground body
// from a pool and creates the ground box shape (also from a pool).
// The body is also added to the world.
b2Body* groundBody = world->CreateBody(&groundBodyDef);

// Define the ground box shape.
b2PolygonShape groundBox;       

// bottom
groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);

// top
groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO));
groundBody->CreateFixture(&groundBox,0);

// left
groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(0,0));
groundBody->CreateFixture(&groundBox,0);

// right
groundBox.SetAsEdge(b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);

Answer 1

// bottom

float screenMid = screenSize.height/2;  // Y axis on screen middle

        groundBox.SetAsEdge(b2Vec2(0,screenMid/PTM_RATIO),b2Vec2(screenSize.width/PTM_RATIO,screenMid/PTM_RATIO));

这会将您的底线转移到屏幕中间。 SetAsEdge 方法取两个点并从点 1 到点 2 画一条线。在上面的陈述中，第一点是“b2Vec2(0,screenMid/PTM_RATIO)”。其中 0 是 x 轴，screenMid 是第一个点的 y 轴。第二点也是如此。

您必须将每个点除以 PTM_RATIO 才能将其转换为 box2d 坐标。