DarkRadiant shader system

The DarkRadiant shader system module is initialised during DarkRadiant startup and parses the material files during this phase.

It consists of a few components:

• The ShaderLibrary which holds all the named ShaderDefinitions and named Shader objects. It gets populated by the ShaderFileParser during startup or when the user requests a shader refresh.
• The GLTextureManager, responsible for "realising" the actual Texture objects (this includes image post-processing like gamma-adjustment and resampling).
• The actual Shader objects.

The Shader and Texture objects are allocated on the heap using boost::shared_ptrs.

Note that the actual image data isn't loaded until they are requested by the render system. If the latter requests a TexturePtr by calling Shader::getDiffuse(), the Shader object checks the contained TexturePtr for realisation. If the TexturePtr is still NULL, it sends a request to the GLTextureManager for the Texture to be realised. This happens by passing the TextureConstructor to the GLTextureManager, which can be used to retrieve an Image object containing the raw pixel data.