A testbed example that reproduces the problem is ideal. ![]() You can help to ensure your issue gets fixed if you provide sufficient detail. Please file bugs and feature requests here: Box2D Issues The latest version of Box2D may be out of sync with this manual. This manual is only updated with new releases. Please look at the testbed included with Box2D to learn more. This manual covers the majority of the Box2D API. There are many resources for this on the net. Please learn C++ programming, compiling, linking, and debugging before working with Box2D. Box2D should not be your first C++ programming project! You should be comfortable with compiling, linking, and debugging.Ĭaution: Box2D should not be your first C++ project. Since Box2D is written in C++, you are expected to be experienced in C++ programming. You can get these tutorials from the download section of. If not, please first consult Google search and Wikipedia.īox2D was created as part of a physics tutorial at the Game Developer Conference. In this manual I'll assume you are familiar with basic physics concepts, such as mass, force, torque, and impulses. Hopefully this is sufficient to avoid name clashing with your game engine. ![]() Most of the types defined in the engine begin with the b2 prefix. From the game engine's point of view, a physics engine is just a system for procedural animation.īox2D is written in portable C++. Programmers can use it in their games to make objects move in realistic ways and make the game world more interactive. For example, if sharing was the default, and the second subscriber wouldn't want to share and removes the sharing - what about the third one? Will it share it with the first one or not? At that point the sharing property becomes the property of the Subscriber and not the Observable and you would have no clear way of knowing which one is shared and which one isn't.Box2D is a 2D rigid body simulation library for games. Or if you wanted to start a timer whenever you're subscribed, you again wouldn't want to share this with other Observables.Īlso, it is much easier to add certain behaviour than to remove it. But what if you we're updating something on the backend, using the same network and method call from two different points, updating with different data? You would have the same call with the same Observable, but you certainly wouldn't want to share the Observable instance (and the network call) because that means that all successive calls with data would be discarded in the favour of the first one. In the above code, yes, sharing makes sense. I'm afraid that you will have to think when programming. ![]() I would not have to think about when I need to share an Observable, and when I don't. A cold Observable is known to talk only to a single Observer so there is no need for the extra tracking overhead. However, multicasting is expensive on itself because you have to keep track of the set of current Observers in order to notify them with new events, and this can lead to all sorts of logical race conditions to be defended against. Why is not share() the default behavior for all observables?Īctually, this property is one of the important contributions of the modern reactive programming paradigm: the distinction of the hot and cold Observables. ![]() If your source is already hot, you don't need share(). However, often it is not economic to keep an originally cold Observable running after all Observers of publish() have gone away, therefore the refCount() operator can be used to keep track of them and stop the source when there are no interesting parties left. Thus, the chain will now act as a hot multicasting Observable from the Observers' perspective. To turn a cold Observable into a hot one, you can use publish() which will make sure only a single subscription is established to the source Observable no matter how many Observers there are. An example of this is an Observable of button clicks. These Observables usually multicast the same items to all of their current Observers. In contrast, a hot Observable can produce items with or without the presence of Observers. An example of this is an Observable that issues a network request. Subscribing with multiple Observers will result in multiple runs of the same cold Observable. Cold Observables start producing items when there is an Observer to them and they do it on an individual basis. There are two kinds of Observables: cold and hot.
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