WebGL is an API for rendering graphics in web browsers, which is based on the functionality of the OpenGL ES graphics library. WebGL 1.0 roughly matches OpenGL ES 2.0 functionality, and WebGL 2.0 roughly matches OpenGL ES 3.0 functionality.
Unity WebGL only supports Deferred Rendering Path if WebGL2.0 is available. On WebGL1.0, Unity WebGL runtime will fallback to Forward Rendering.
Unity WebGL only supports baked GI. Realtime GI is not currently supported in WebGL. Furthermore, only Non-Directional lightmaps are supported.
Unity WebGL does not support Procedural Materials at runtime. Like on other unsupported platforms, Procedural Materials will be baked into ordinary Materials during the build.
WebGL does not support linear color space rendering.
WebGL does not support playing Video using the MovieTexture class. However, you can efficiently play back video in your WebGL content using the HTML5 video element. Download this Asset Store package for an example of how to do so.
The WebGL 1.0 specification imposes some limitations on GLSLS shader code, which are more restricted then what many OpenGL ES 2.0 implementations allow. This is mostly relevant when you write your own shaders.
Specifically, WebGL has restriction on which values can be used to index arrays or matrices: WebGL only allows dynamic indexing with constant expressions, loop indices or a combination. The only exception is for uniform access in vertex shaders, which can be indexed using any expression.
Also, restrictions apply on control structures. The only type of loops which are allowed are counting for loops, where the initializer initializes 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. for loops which don’t match those criteria and while loops are not allowed.
Unity WebGL supports dynamic font rendering like all Unity platforms. However, it does not have access to the fonts installed on the user’s machine, so any fonts used must be included in the project folder (including any fallback fonts for international characters, or bold/italic versions of fonts), and set up as fallback font names.
WebGL supports anti-aliasing on most (but not on all) combinations of browsers and GPUs. To use it, anti-aliasing must be enabled in the default Quality Setting for the WebGL platform. Switching quality settings at runtime will not enabled or disable anti-aliasing - it has to be set up in the default Quality Setting loaded at player start up. Note that the diffent multi sampling levels have no effect in WebGL. In addition, be aware that any Image Effect applied to the camera disables the built-in Anti-Aliasing on WebGL1.0. There is no such limitation on WebGL2.0.
Reflection probes are supported in WebGL, but due to limitations in the WebGL specification about rendering to specific mipmaps, smooth realtime reflection probes are not supported (so realtime reflection probes will always generate sharp reflections, which may appear very low-resolution). Smooth realtime reflection probes will require WebGL 2.0.
Unity includes support for the WebGL 2.0 API, which brings OpenGL ES 3.0-level rendering capabilities to the web. This feature is not yet enabled in any shipping browser by default, but can be enabled in current builds in Firefox (webgl.enable-prototype-webgl2 in about:config) and Chrome (WebGL 2.0 Prototype in chrome://flags)
By default, Unity WebGL builds support both WebGL 1.0 and WebGL 2.0 APIs, This can be configured in the WebGL Player Settings > Other Settings; to do this, uncheck Automatic Graphics API.
When WebGL 2.0 is supported in browsers, content can benefit from a better quality in the Standard Shader, directional lightmap support, no restrictions on indexing and loops in shader code, and better performance.