Web performance considerations

In general, Web performance is close to native apps on the GPU, because the WebGLA JavaScript API that renders 2D and 3D graphics in a web browser. The Unity Web build option allows Unity to publish content as JavaScript programs which use HTML5 technologies and the WebGL rendering API to run Unity content in a web browser. More info
See in Glossary graphics API uses your GPU for hardware-accelerated rendering. The only exception is the slight overhead for translating WebGL API calls and shadersA program that runs on the GPU. More info
See in Glossary to your OS graphics API (typically DirectX on Windows, OpenGL on Mac, and Linux).

On the CPU, Emscripten translates your code into WebAssembly, the performance of which depends on the web browser you’re using.

Be aware of the following considerations:

• Unity provides multithreading for C/C++ code, but not yet for C# code due to limitations of WebAssembly.
• When using WebGL API for rendering, the CPU side dispatch of WebGL operations is slower than in native OpenGL. As a result, for best performance, the recommended best practice is to avoid large numbers of draw calls per frame, so make sure that both instancing and batching techniques are used in your shaders.
• SIMD on the web is supported as part of WebAssembly 2023 feature setA feature set is a collection of related packages that you can use to achieve specific results in the Unity Editor. You can manage feature sets directly in Unity’s Package Manager. More info
  See in Glossary. Make sure to enable WebAssembly 2023 for best performance on newer browsers.

Tip: To learn how Unity distributes work to different threads on non-Web platforms, refer to the new timeline 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 in Unity.

Web-specific settings which affect performance

To improve performance, set Exception support to None in the Player settings for Web by expanding Other Settings > Stack Trace.

Collect performance data with the Profiler

You can use the Profiler in the Web platform, but you can’t attach to a running player built with Web through the Editor. This is because the WebGL API uses WebSockets for communication, which doesn’t allow for incoming connections on the browser side.

To attach to a running player, you need to enable the Autoconnect Profiler setting:

1. Open the Build Profiles window (menu: File > Build Profiles).
2. Select the Web platform.
3. Enable the Development BuildA development build includes debug symbols and enables the Profiler. More info
   See in Glossary setting.
4. Enable the Autoconnect Profiler setting.

Note: Unity can’t profile draw calls for Web applications.

For more information, refer to Connecting the Profiler to a data source.

Web content in background tabs

Your content continues to run when the canvas or browser window loses focus if one of the following options is enabled:

• Run in background in the Player settings for the Web platform
• Application.runInBackground

However, some browsers can throttle content running in background tabs. If the tab with your content isn’t visible, your content only updates once per second in most browsers. Note that this causes Time.time to progress slower than usual with the default settings, as the default value of Time.maximumDeltaTime is lower than one second.

Throttling Web performance

You might want to run your Web content at a lower frame rate in some situations to reduce CPU usage. For example, on other platforms, you can use the Application.targetFrameRate API to do so.

When you don’t want to throttle performance, set this API to the default value of –1. This allows the browser to adjust the frame rate for the smoothest animation in the browser’s render loop, and might produce better results than Unity trying to do its own main loop timing to match a target frame rate.

Note: For security reasons, Unity can’t query a browser for its frame rate. As a result, Unity assumes a display rate of 60 fpsSee first person shooter, frames per second.
See in Glossary for all browsers and bases Application.targetFrameRate on that value.