Create samples or docs showing how to do post processing

[vchelaru]

Look at Miguel's effects:

https://github.com/mfigueirido/AdaptableCrtEffect

and render targets:

https://docs.flatredball.com/flatredball/api/flatredball/graphics/layer/rendertarget

[vchelaru]

First step is to add support for DefaultLayer in Screens. That's been added here:

https://app.gitbook.com/o/-M_fyYVTQKWSV65sXTSp/s/-M_fye9Ufg3vzJxwX5Hk/glue-reference/screen/defaultlayer

[vchelaru]

• Add PostProcess for global post processing in FRB
• Add sample .fx file to Glue
• Create dropdown/radio button to select the type of post process to use - pictures would be good!
• Create Bloom post process .fx and modify .cs
• Create CRT effect post process .fx and modify .cs
• Create blur post process .fx and modify .cs
• Create pixellate post process .fx and modify .cs