WebGL 是一种用于在 Web 浏览器中渲染图形的 API，基于 OpenGL ES 图形库的功能。WebGL 1.0 大致与 OpenGL ES 2.0 功能相匹配，而 WebGL 2.0 大致与 OpenGL ES 3.0 功能相匹配。
By default, Unity WebGL clears the drawing buffer after each frame, which means the content of the frame buffer clears regardless of the Camera.clearFlags setting. However, you can change this behavior at instantiation time. To do this, set webglContextAttributes.preserveDrawingBuffer to true in your WebGL template:
```
script.onload = () => {
config[‘webglContextAttributes’] = {“preserveDrawingBuffer”: true}; // 在 WebGL 模板中将此文件添加到 index.html 文件中
createUnityInstance(canvas, config, (progress) => }
```
Unity WebGL only supports Deferred Rendering Path if WebGL2.0 is available. On WebGL 1.0, Unity WebGL runtime falls back to Forward Rendering.
Unity WebGL only supports baked GI. Realtime Global Illumination isn’t currently supported in WebGL. In addition, Unity WebGL supports Non-Directional lightmaps only.
采用 WebGL 2.0 时，Unity WebGL 仅支持线性颜色空间渲染。线性颜色空间渲染不支持回退到 WebGL 1.0。要使用线性颜色空间渲染来构建 WebGL 播放器，必须在 Player 设置中打开的 Other Settings 面板中删除 WebGL 1.0 API，并禁用 Automatic Graphics API 设置。
某些 Web 浏览器不支持 sRGB DXT 纹理压缩。因此在使用线性渲染时会降低渲染性能的质量，原因是所有 DXT 纹理都要在运行时解压缩。
You can’t use VideoClipImporter to import video clips to your Unity project, because it might increase the initial asset data download size and prevent network streaming. For video playback, use the URL option in the VideoPlayer component and place the asset in the StreamingAssets/ directory to use the built-in network streaming of your browser.
The WebGL 1.0 specification imposes some limitations on GLSLS shader code, which are more restrictive than most OpenGL ES 2.0 implementations. This is mostly relevant when you write your own shaders.
WebGL has specific restrictions on which values to use to index arrays or matrices. For example, WebGL only allows dynamic indexing with constant expressions, loop indices or a combination, except for uniform access in vertex shaders, which you can index using any expression.
Note for WebGL 1.0: Additional restrictions apply on control structures in WebGL 1.0, where it doesn’t allow while loops and most type of for loops. However, it allows counting for loops, where the field initializer sets a variable to a constant, the update adds a constant to or subtracts a constant from the variable, and the continuation test compares the variable to a constant.
Note: Due to limited available memory in WebGL, you should avoid including unneeded shader variants which can lead to unnecessary memory usage. Therefore, Unity recommends familiarizing yourself with shader variants and shader stripping, and take extra care to ensure that you don’t add shaders with too many variants (for example, Unity’s Standard Shader) to the [Always-included Shaders] section(class-GraphicsSettings#Always) in Graphics Settings.
Unity WebGL supports dynamic font rendering similar to other Unity platforms. However, as it doesn’t have access to the fonts installed on the user’s machine, if you want to use any fonts, make sure to include them in the project folder (including any fallback fonts for international characters, or bold/italic versions of fonts), and set as fallback font names.
WebGL 对于大多数（但不是全部）浏览器和 GPU 组合均支持抗锯齿功能。要使用抗锯齿功能，必须在 WebGL 平台的默认 Quality 设置中启用该功能。
Unity WebGL supports all reflection probes. Note: WebGL 1.0 doesn’t support Smooth realtime reflection probes.
Unity 包含对 WebGL 2.0 API 的支持，因此为 Web 带来了 OpenGL ES 3.0 级的渲染功能。
By default, Unity WebGL builds support the WebGL 2.0 API. You can configure this in the WebGL Player settings > Other Settings panel by disabling the Automatic Graphics API property and adding the WebGL 1.0 API to your project.
Browsers with WebGL 2.0 support have the following advantages:
可以在运行时使用 SystemInfo.graphicsDeviceType 来确定 Unity 实例是使用 OpenGLES3 (WebGL2.0) 还是 OpenGLES2 (WebGL1.0) 进行渲染。