We have covered a lot so far. However, we have not discussed one very important thing: how to hide virtual things behind physical things.

I have shown you the virtual puppy hiding behind my living room chair. How do we do this? The answer is: using the right kind of shader.

We have mentioned shaders before, but now it is time to delve a little bit more deeply into them.

In DirectX, we have a whole set of shaders: we have seen pixelshaders, geometryshaders, and vertexshaders. There are a lot more, but we will not go into those at all.

In Unity3D we only have one, simply called the shader. The shader we use is a property of the material we apply.

Let us create a new one. In our Unity3D project, create a new shader. Call it Occlusion. You do this by right-clicking in the Assets pane and selecting the relevant menu options, as shown in the following screenshot:

Creating a shader

Double-click on the newly created file and you will get the following code:

Shader "Custom/Occlusion" { 
   Properties...