This third instalment on Volumetric Rendering will explain how to shade volumes in a realistic fashion. This essential step is what gives threedimensionality to the flat, unlit shapes that have been generated so far with raymarching.

You can find here all the other posts in this series:

# Vertex and fragment shaders in Unity3D

Part 1, Part 2, Part 3, Part 4, Part 5, [download the Unity3D package]

The previous three posts of this tutorial have introduced surface shaders and how they can be used to specify physical properties (such as albedo, gloss and specular reflections) of the materials we want to model. The other type of shader available in Unity3D is called vertex and fragment shader. As the name suggests, the computation is done in two steps. Firstly, the geometry is passed through a function called (typically called `vert`) which can alter the position and data of each vertex. Then, the result goes through a `frag` function which finally outputs a colour.

# Physically Based Rendering and lighting models in Unity3D

Part 1, Part 2, Part 3, Part 4, Part 5, [download the Unity3D package]

Why is it colder at the poles and hotter on the equator? This question, which seems completely unrelated to shaders, is actually fundamental to understand how lighting models work. As explained in the previous part of this tutorial, surface shaders use a mathematical model to predict how light will reflect on triangles. Generally speaking, Unity supports two types of shading techniques, one for matte and one for specular materials. The former ones are perfect for opaque surfaces, while the latter ones simulate objects which reflections. The Maths behind these lighting models can get quite complicated, but understanding how they work is essential if you want to create your own, custom lighting effect. Up to Unity4.x, the default diffuse lighting model was based on the Lambertian reflectance. Continue reading

Part 1, Part 2, Part 3, Part 4, Part 5

This is the second part of a series of posts on Unity3D shaders, and it will focus on surface shaders. As previously mentioned, shaders are special programs written in a language called Cg / HLSL which is executed by GPUs. They are used to draw triangles of your 3D models on the screen. Shaders are, in a nutshell, the code which represents how different materials are rendered. Surface shaders are introduced in Unity3D to simplify the way developers can define the look of their materials.

# A gentle introduction to shaders in Unity3D

Part 1, Part 2, Part 3, Part 4, Part 5

We can safely say that Unity3D has made game development easier for a lot of people. Something where it still has a long way to go is, with no doubt, shader coding. Often surrounded by mystery, a shader is a program specifically made to run on a GPU. It is, ultimately, what draws the triangles of your 3D models. Learning how to code shaders is essential if you want to give a special look to your game. Unity3D also uses them for postprocessing, making them essential for 2D games as well. This series of posts will gently introduce you to shader coding, and is oriented to developers with little to no knowledge about shaders.

### Introduction

The diagram below loosely represents the three different entities which plays a role in the rendering workflow of Unity3D: