物理模拟

At physics simulation, physics calculations are in the multi-threaded mode — some operations are performed in parallel.在物理模拟中，物理计算在多线程模式——一些操作是并行执行的。

Physics performance profiler enables real-time tracking of simulation performance.物理性能分析器可以实时跟踪仿真性能。

注意

To show the physics performance profiler that reports statistics on different physics simulation aspects, press 1 hotkey three times or type show_profiler_physics  1 in the console.展示物理性能剖析器报告不同物理模拟方面的统计信息，按 1 热键三次或在控制台中键入 show_profiler_physics  1。

UNIGINE physics module performs all its calculations. There are few things to point out about physics. UNIGINE 物理模块执行所有计算。关于物理学，有几件事需要指出。

• It is simulated with its own fixed FPS, which does not depend on the rendering framerate. (The Engine FPS can also be synchronized with the physics one).它是用它模拟的拥有固定的FPS ， 哪一个不依赖关于渲染帧率。 （引擎 FPS 也可以是同步的与物理之一）。

  注意

  If physics takes more than the assigned budget, further calculations are delayed. These calculations shall be performed during the subsequent rendering frames, making physics simulation look like in a "slow-motion" mode. The default budget is 50ms, but it can be increased, as necessary.如果物理学比分配的预算，进一步的计算被延迟。这些计算应在随后的渲染帧期间执行，使物理模拟看起来像在“慢动作”模式下。默认预算为 50ms，但可以根据需要增加。

• During each tick, a number of calculation iterations can be performed. This includes the full cycle of physics simulation:在每个滴答声中，计算数迭代可以执行。这包括物理模拟的完整周期：

  1. updatePhysics() from the world logic is called.updatePhysics() 从世界逻辑被调用。
  2. Collision detection is performed.碰撞检测被执行。
  3. Joints are solved.关节解决了。
  4. Collision response is performed.碰撞响应被执行。
  注意

  There is no point in setting the number of iterations too high. UNIGINE checks whether the next iteration can be performed within physics budget limit, and if not, it is delayed and moved to the next rendering frame.设置没有意义迭代次数太高。 UNIGINE 检查下一次迭代是否可以在物理预算限制，如果不是，则延迟并移动到下一个渲染帧。

There are two update modes available for physics simulation (each of them has its advantages and use cases):物理模拟有两种可用的更新模式（每种都有其优点和用例）：

• Before Rendering — physics update (along with the spatial tree update and user callbacks) is executed in the Main thread just before rendering is performed (render). The number of physics ticks executed before the rendering frame here is defined by the physics and the Engine framerates. This mode is the most clear and straightforward (everything is executed safely in a strictly determined order) with no frame lag (results of physics calculations are applied in the current frame). But, on the other hand, this mode is the slowest as there are no asynchronous parallel calculations (everything's in the Main thread). Use this mode in case the time lag is unacceptabe for your application (you need all physics calculations to be applied in the current frame) and you want maximum simplicity and strictly determined order of execution for user code (physicsUpdate and physics callbacks). Before Rendering — 物理更新（连同空间树更新和用户回调）在渲染执行之前在主线程中执行（render）。此处渲染帧之前执行的物理滴答数由物理和引擎帧率. 此模式最清晰直接（一切都以严格确定的顺序安全执行），没有帧滞后（物理计算的结果应用于当前帧）。但是，另一方面，这种模式是最慢的，因为没有异步并行计算（一切都在主线程中）。 如果您的应用程序无法接受时间延迟（您需要在当前帧中应用所有物理计算）并且您希望最大程度地简化并严格确定用户的执行顺序，请使用此模式代码（physicsUpdate 和物理回调）。
• Async Rendering — physics update is performed asynchronously to rendering. In case of several physics ticks per one rendering frame (when the Engine framerate is lower, or catching up is performed), only the first one is executed in parallel, then the physics module waits for the completion of the rendering process, returns to the Main thread and executes the rest of the physics ticks. There is a frame lag (results of physics calculations are applied in the next frame) and there is some ambiguity regarding the time, when user code (physicsUpdate and physics callbacks) is to be executed in case of several physics ticks per one rendering frame (some part is executed before rendering while the other just after it). This mode is the fastest one and is used by default.Async Rendering — 物理更新与渲染异步执行。如果每个渲染帧有多个物理滴答（当引擎帧速率较低时，或赶上执行），仅并行执行第一个，然后物理模块等待渲染过程完成，返回主线程并执行其余的物理滴答。存在帧延迟（物理计算的结果在下一帧中应用），并且在每个渲染帧有多个物理滴答的情况下执行用户代码（physicsUpdate 和物理回调）的时间存在一些歧义（某些部分在渲染之前执行，而另一部分则在渲染之后执行）。此模式是最快的，默认使用。

The modes are toggled in Global Physics Settings in UnigineEditor.模式在全局物理设置在 UnigineEditor 中。

Catching Up

迎头赶上#

Deterministic mode ensures that all contacts are solved in the predefined order and visualization of physics in the world is repetitive (on one computer). When this mode is enabled the Engine performs additional sorting of bodies, shapes and joints inside islands after building them.确定性模式确保所有接触都以预定义的顺序解决，并且世界上的物理可视化是重复的（在一台计算机上）。启用此模式后，引擎会在构建岛屿后对岛屿内的物体、形状和关节进行额外的排序。

Deterministic mode is unavailable in case there are missed frames — it is simply impossible. Moreover, there may be differences between visualization of physics on different hardware (e.g., AMD and Intel).确定性模式在丢失帧的情况下不可用——这根本不可能。此外，不同硬件（例如 AMD 和 Intel）上的物理可视化可能存在差异。

Determinism is guaranteed if there are no missed frames, the same Engine version is used, and the CPUs perform SSE operations similarly.如果没有丢失帧，使用相同的引擎版本，并且 CPU 执行类似的 SSE 操作，则可以保证确定性。

Please note that deterministic mode does not come for free, it may eat up to 10-20% of the frame rate, and it also depends on the scene a lot.请注意，确定性模式可能会影响性能，它可能会吃掉高达 10-20% 的帧速率，而且它也很大程度上取决于场景。

The mode can be enabled in Global Physics Settings in UnigineEditor.该模式可以在全局物理设置在 UnigineEditor 中。

Simulation of physics goes through a number of stages when it is updated each iteration. They are as follows.物理模拟在每次迭代更新时都会经历多个阶段。它们如下。

1. Physics update物理更新
2. Сollision detection碰撞检测
3. Simulation模拟
4. Synchronization of physics物理同步

In the performance profiler, the total time of physics simulation is displayed by the Physics counter.在表演中剖析器，物理模拟的总时间由Physics计数器显示。

1. Physics Update

1.物理更新#

2. Collision Detection

2. 碰撞检测#

3. Simulation

3. 模拟#

4. Synchronization of Physics

4.物理同步#

Synchronization is the final stage of physics simulation. During the swap() in the UNIGINE main loop, physics module calls its internal updatePhysics() function. Bodies set their calculated transformations to objects. In the next frame, objects will be rendered in their new physics-based positions.同步是物理模拟的最后阶段。在 UNIGINE 主循环中的 swap() 期间，物理模块调用其内部的 updatePhysics() 函数。物体将其计算的变换设置为对象。在下一帧中，对象将在其新的基于物理的位置进行渲染。

注意

In the Async Rendering update mode physics simulation goes in parallel to the actual rendering process. This is the reason calculated physics is visible only in the next frame.在 Async Rendering 更新模式下物理模拟并行进行到实际的渲染过程。这就是计算物理仅在下一帧可见的原因。

If visualizer options are enabled, shapes, joints or contacts of non-frozen bodies will be rendered.如果启用了可视化选项，将渲染非冻结体的形状、关节或接触。

Multi-threaded simulation of physics is run when the Async Rendering update mode is selected and there are two or more physics threads.Multi-threaded simulation of physics is run when the Async Rendering update mode is selected and there are two or more physics threads.

1. updatePhysics() from the world script is always performed in the main physics thread.世界脚本中的 updatePhysics() 始终在主物理线程中执行。

2. After that, the Engine takes advantage of multiple CPUs during the collision detection and simulation stage.之后，引擎在运行期间利用多个 CPU碰撞检测和模拟阶段.

   • Contacts for all physical bodies within the physical distance are found along with all necessary information.内所有物理物体的接触物理距离连同所有必要的信息一起找到。
   • Islands are created based on the data on object collisions.岛屿是根据对象碰撞数据创建的。
   • As islands have been created, they can be safely handled in separate threads, because they are isolated.随着孤岛的创建，它们可以在单独的线程中安全地处理，因为它们是隔离的。
   • Then threaded islands are synchronized in the main physics thread to exchange data about the current contacts and ones from the previous frames. It will ensure proper physical behavior of bodies.然后线程岛在主物理线程中同步，以交换有关当前联系人和前一帧联系人的数据。它将确保物体的适当物体行为。
   • From there on, collision response and joints solving are again calculated per island in separate threads.从那里开始，碰撞响应和关节求解再次在单独的线程中按岛计算。

3. Before physics is synchronized with the world, the engine waits for all threads to finish their calculations. When thread synchronization happens (during the swap stage of the UNIGINE main loop), all assigned physics callbacks are executed in the main thread (the order is as follows: bodies, joints, and triggers), and then physics is applied to nodes.在物理与世界同步之前，引擎会等待所有线程完成它们的计算。当线程同步发生时（在 UNIGINE 主循环的 swap 阶段），所有分配的物理回调都在主线程中执行（顺序如下：物体、关节和触发器），然后将物理应用于节点。

   注意

   Physics callbacks (mainly used for creation, destruction or modification of other objects) are called in the main thread, as this is the only place where such operations can be performed safely.物理回调（主要用于创建、销毁或修改其他对象）在主线程中调用，因为这是唯一可以安全执行此类操作的地方。