AR Realtime Environmental Lighting
Github project here:
Captures the camera video frame and uses it for spherical environment mapping. ARKit and ARCore supported.
The main stage are:
Capture the Camera Background
The camera background is blitted to a RenderTexture. This RenderTexture will be smaller then the screen size. This makes the following operations more performant and gives us some cheap filtering when it is downscaled. The blit must be done in a CommandBuffer so that the external camera sampler is access correctly. The texture is accessed in a platform specific way. ARCore relies on an external sampler OpenGLES extension, so requires a GLSL shader. ARKit uses a YCrCb image format with multiple buffers. The shaders reconstructs the RGB color.
Blur the Background
The lighting is an approximation, so we blur the camera blur to avoid bright, flickering highlights.
The background is wrapped around the scene much like a MatCap or spherical environment map. This is not strictly accurate as the camera edges are wrapped around to the front of the object, but gives a "good enough" result in most AR scenes.
The shader calculates the reflection vector and then converts that into a UV coordinate.
There are two ways to light the scene. The first uses Unity's real-time GI system by combining a skybox with reflection and light probes in the scene. This works with any existing materials. The view direction must be corrected in the skybox shader to account for the pass for each skybox face.
The second uses the "finalcolor" function in a shader, so it requires a customer shader. This method is more performant.

John Sietsma
Unity Evangelist - Other