Cg/HLSL shaders

The shading language used in Unity is a variety of HLSL, or sometimes referred to as Cg. This shading variant provides two different forms of shaders: surface and vertex/fragment shaders. Now, coming from Android, this may sound confusing, since GLSL treats vertex and fragment shaders differently. However, variety of HLSL in Unity treats vertex and fragment shaders as the same, since they reside in the same file and are in the same workflow. A surface shader, which handles the lighting of our model, can be simple or quite complex. The Standard Unity surface shader uses a PBR lighting model, which is quite advanced and not supported on most mobile devices. This issue, combined with our limited ability to track scene lights, limits us to writing our own shaders in order to get our object lighting correct. ARCore provides us with a very simple surface shader that is used in the sample to light the Andy model. Let's open up Unity and take a look at what that shader looks like...