Let's see in practice how we integrate our ESSL program to our WebGL code by working on a simple example from scratch.
We have a wall composed of the sections A, B, and C. Imagine that you are facing section B (as shown in the following diagram) and that you have a flashlight on your hand (Frontal View). Intuitively section A and section C will be darker than section B. This fact can be modeled by starting at the color of the center of section B and darkening the color of the surrounding pixels as we move away from the center.
Let's summarize here the code that we need to write: