如何用box2d让b2body匀速移动

发布于 2024-12-06 07:54:20 字数 279 浏览 0 评论 0原文

我正在制作一个 box2d 游戏，让敌人从屏幕左侧飞到屏幕右侧。如果我在刻度方法中施加如下所示的力，敌人会随着时间的推移移动得越来越快。我希望敌人以恒定的速度移动，而不是加快速度。我该怎么办呢。我尝试过冲动和力量，但它们似乎并没有保持恒定的速度

b2Vec2 forceA = b2Vec2(15, -b->GetMass() * world->GetGravity().y);
b->ApplyForce(forceA, b->GetWorldCenter() );

原文

I am making a box2d game and have enemies fly in from the left side of the screen to the right side of the screen. If I apply a force in the tick method like shown below, the enemies increasingly move faster over time. I want the enemies to move at a constant pace instead of increasing their speed. How can I do this. I have tried impulses and forces, but they don't seem to keep a constant speed

b2Vec2 forceA = b2Vec2(15, -b->GetMass() * world->GetGravity().y);
b->ApplyForce(forceA, b->GetWorldCenter() );

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叹倦 2024-12-13 07:54:20

只需以您想要的速度创建它们：

b2BodyDef bDef;
...
bDef.linearVelocity = myVelocity;
b2Body *b = world->createBody(&bDef);

如果没有向它们施加力，它们将根据牛顿第一定律保持其速度。如果有重力，则每一步都会施加力：

b2Vec2 forceA = b2Vec2(0, -b->GetMass() * world->GetGravity().y);
b->ApplyForce(forceA, b->GetWorldCenter() );

Just create them with the speed you want:

b2BodyDef bDef;
...
bDef.linearVelocity = myVelocity;
b2Body *b = world->createBody(&bDef);

If no forces are applied to them they will preserve their speed according to Newton's first law. If you have gravity then each step apply force:

b2Vec2 forceA = b2Vec2(0, -b->GetMass() * world->GetGravity().y);
b->ApplyForce(forceA, b->GetWorldCenter() );

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沙与沫 2024-12-13 07:54:20

使用b->SetLinearVelocity(b2Vec2(thisVel, 0));。如果这个恒定速度最终可能会改变为其他恒定速度，您可以将其包装在一个条件中，例如

if(b->GetLinearVelocity().x != 0){ 
    b->SetLinearVelocity(b2Vec2(0, 0));
}

这样您就不会在每个刻度处重新应用相同的速度（尽管 box2d 可能会为您处理这个问题，对此不太确定）。

我遇到了同样的问题，即如何使身体以恒定速度移动，我建议的另一件事是确保您的身体移动的表面/介质是无摩擦的 - 这样它们在移动后就不会减慢速度你设置他们的速度。

use b->SetLinearVelocity(b2Vec2(thisVel, 0));. If this constant velocity might eventually be changed for some other constant velocity, you could wrap this in a conditional such as

if(b->GetLinearVelocity().x != 0){ 
    b->SetLinearVelocity(b2Vec2(0, 0));
}

So that you're not re-applying the same velocity each tick (although it's possible that box2d takes care of this for you, not sure about that).

I ran into the same issue of how to make bodies move at a constant speed, and the one other thing I recommend is to make sure the surface/medium that your body is moving across is frictionless - that way they'll never slow down after you set their velocity.

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