How can I make a censored surface on my mesh? I want select a little portion of my mesh or create a new geometry to apply on my mesh to censor with pixels what I see in that little portion.
Just give the polygons you want to censor a black material.
My model has a texture. I want keep inalterate the texture. Is there a way to apply a sort of mask that make the classic censored effect?
You can apply a second material to the model and use this material only on the relevant polygons.
Which classic? I can think of black bar (box mask with color), blur (box mask with blurred image), and pixelization - all in post of course. I would have to toy around with the pixelization, can’t do that right now.
I mean this effect: https://blender.stackexchange.com/questions/41452/how-to-make-pixelated-censor-effect
I want paste that square on my model.
Ah, that would be done in post production with the compositor.
Yeah but I can’t follow that guide, maybe blender 2.8 is different.
I don´t think so. What exactly isn´t working?
I don’t know, I even try to download the blender file from that site but when I load the scene I don’t see the pixalated effect.
I didn’t download the file, but the process:
Image -> Scale Down -> Pixelate -> Inpaint -> Scale Up
seem to work for me. Then you have a pixelated image you can mix with the original.
Ah the pixelated effect is only in the render image. So I can’t see the effect in the 3D Viewport, right?
But this is not what I want. I want to able to export my model (with the pixelated effect) in other program such as game engine, so I need a way to create that effect through shader editor node.
I don’t think that’s possible on its own – what you could do is make an object to “shield” the area you want censor-pixelation on, then make a material for it that resembles a censor-pixelation effect.
Even then, a 3D program’s material nodes may not translate into whichever game engine you’re making this for, never mind all of them (like if you’re making this as a general gaming resource) – you’ll probably need to bake your material to texture maps.
Yeah, baking seems like the only approach. All the things I can think of involves use of empty/mask in combination with window coordinates to mess up the original material - none of which would be available to a game engine. With “think of” it doesn’t mean I would be able to pull it off 
but that would likely be my attack angle.
Say you want this on a characters eyes. Feels impossible to make it work for different angles for a bake; if he rotates, effect will be squished. Also a pixelated effect would also pixelate the background, I can’t think of a way this could be achieved in “a material”.
As for pixelated; I guess you can apply the above technique, but instead of using a finished render you apply it to the texture map image file, save out that, then reattached it? I can’t imagine it will look as you expect though.
You could select a portion or create duplicate and move away from original, select and parent to the original object, and then select shade flat to enhance the faces. Add a Solidify Modifier to give it some area, and add a glass shader with transparency …play with the IOR setting and roughness…and get something like this…
If you’re intending to render on another engine, you really need to be doing the effect on that other engine. Materials are not compatible between engines. Blender can, at best, bake you some textures if you decide you need them, but the kind of censoring you’re describing is a view-dependent effect that textures alone will never be able to capture (but actual shader coding will.)
The only idea I can come up with is to place a plane in front of the area, subdivide it a few times, use the principled bsdf node to turn up the transmission all the way and, using multiple materials on the one plane, set different IOR factors (and maybe roughness values) to the individual faces.
if this works how I’m imagining, it should create a sort of floating pixelated blur effect in front of your model with different faces having different magnifications (IOR) and blur (roughness). You could parent the plane to the model so that it moves with it, as well.
disclaimer: I’m not at my computer right now, so I can’t test this.