Physics Profiler module

The Physics ProfilerA window that helps you to optimize your game. It shows how much time is spent in the various areas of your game. For example, it can report the percentage of time spent rendering, animating, or in your game logic. More info
See in Glossary module displays information about the physics that the physics system has processed in your project’s sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary. This information can help you diagnose and resolve performance issues or unexpected discrepancies related to the physics in your project’s scene. You can also use the Physics Debug Visualization to further debug and understand issues with physics in your application.

Chart categories

The Physics Profiler module’s chart tracks the time your application spends on physics. The timings are divided into different chart categories. To change the order of the categories in the chart, you can drag them in the chart’s legend. You can also click a category’s colored legend to toggle its display. When you click on the chart, you can see the exact numerical values of each chart category in the module details pane below the chart.

Module details pane

When you click on the Physics Profiler module, the module details pane displays further information about the physics in your project’s scene.

The numbers displayed in the Profiler might not correspond to the exact number of GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary with physics components in your Scene. This is because Unity processes some physics components at a different rate depending on which other components affect it (for example, an attached Joint component). To calculate the exact number of GameObjects with specific physics components attached, you must write a custom script with the FindObjectsOfType function.

The Physics Profiler module doesn’t display the number of sleeping Rigidbody components. These are components which don’t engage with the physics system, so the Profiler doesn’t process them. For more information on sleeping Rigidbody components, see the documentation on Rigidbody.

Understanding physics performance issues

The physics simulation runs on a separate fixed frequency update cycle from the main logic’s update loop, and can only advance time via a Time.fixedDeltaTime per call. This is similar to the difference between Update and FixedUpdate. For more information on this, see the documentation on the Time window.

When a heavy logics or graphics frame takes a long amount of time, the Profiler has to call the physics simulation multiple times per frame. This means that an already resource-intensive frame takes even more time and resources. This might cause the physics simulation to temporarily stop according to the Maximum Allowed Timestep value, which you can set in the Project Settings window (menu: Edit > Project Settings > Time)

To detect this in your Project, select the CPU Usage Profiler module and check the number of calls for Physics.Processing or Physics.Simulate in the Overview section in the Hierarchy view.

In this example image, the value of 2 in the Calls column indicates that the physics simulation was called two times over the last logical frame.

A call count close to 10 might indicate an issue. As a first solution, reduce the frequency of the physics simulation, and if the issue continues, check what might have caused the heavy frame before the physics system had to use a lot of simulation calls to catch up with the game time. Sometimes, a heavy graphics frame might cause more physics simulation calls later on in a Scene.

For more detailed information about the physics simulation in your Scene, select the search box at the top of the module details pane, search for Physics.Processing, and then select Calls from the dropdown at the top right of the pane. This displays the names of the physics system tasks that run to update your Scene. The two most common names you’re likely to see are:

• Pxs: short for ‘PhysX solver’, which are physics system tasks that jointsA physics component allowing a dynamic connection between Rigidbody components, usually allowing some degree of movement such as a hinge. More info
  See in Glossary require as well as resolving contacts for overlapping Rigidbody components.
• ScScene: used for tasks that update the Scene, run the broad phase and narrow phase, and integrate Rigidbody components (moving them in space due to forces and impulses). For more information, see Steven M. LaValle’s work on Planning Algorithms for a definition on two-phase collision detection phases.

Legacy Physics Profiler module

You can switch to the Legacy mode to see the older version of the Physics Profiler module, which was the default module in older versions of Unity. To do this, select Legacy from the dropdown menu in the top right of the Physics Profiler module’s details pane.

In this mode, you can load and inspect Profiler data that was saved in an older version of Unity. If you switch to this mode to inspect data captured in a newer version of Unity, then the data displayed is unreliable and inaccurate. You should always use the Current mode to inspect new Physics Profiler data.