Hi all!

I'm wanting to make a velvet shader, i'm sure it's very easy to have that with the function editor, but how?

Try this. In the Highlight dialog select "variable highlights" then go to edit funtion. Insert an Iput node set to "angle of incidence". Back in the Highlights dialog make your global intesity 100% and your Global size 20%. That will give you the basic sheen. The rest will depend on the objects geometry and/or bump/displacement maps.

Good luck.

Creating a displacement map for velvet is time consuming, but not impossible.  The closest example is the Spiky displacement material.  

You would have to create a map with much smaller spikes much closer together, that resemble fibers on the order of one eighth the size of human hair.  That would create a tremendous amount of geometry to render.  However, with a good 2D Graphic Editor, and lots of patience, you could draw the map.