How comes we can’t use them on unity? 
There is bump mapping, so why not Displacement maps as well?
Or there is a way but you have to write plugin or something yourself?
you would just have to write a shader
the reason they are normally not used is that they make no sense in realtime.
the idea of normal maps and parallax maps is that you pretend that there are more polygons than there really are to get a good performance.
displacement maps require real geometry to be present to do something and if you have 50k vertices on the model, you don’t need any pixel shader anymore to pretend detail or better put: it would be an insane waste of performance. (exception: terrains that use displacement shaders to morph the height on a static meshbuffer)
I wonder if we might see a use for displacement maps when DX11 is supported. Real time hardware tessellation! Woot!
nope
simply because it will take till 2013 until opengl reached that point too.
at the time they would be happy to be on a stable standardized dx10 level already
Another classic 
Displacement is very, very slow. Especially since there’s no real benefit to using it procedurally unless the map you’re using to displace with is dynamic (ie, even MORE processor intensive).
It would make sense to use it with tesselation, but once again you’ll mostly end up seeing it being used on water, terrain…
It is actually quite unsuitable for damage/wreckage/destroying things.
Probably for the same reason that curved surfaces remained a curiosity feature of the Quake3 engine: they are just not that practical for use in games
While displacement maps (and curved surfaces too) sound ideal for adding detail during rendering, they are a PITA when you consider other aspects such as culling and collision detection.
Ahh ok, thanks guys.
There is a game engine that does exactly that, but I can’t remember the name of the developer.
I myself thought real time subdivision would make a lot of sense if you compare it to load times of higher res meshes.
The same idea applies to a renderer that can push millions of poly’s at render time,… but if you try to load a million poly mesh into max or maya, it brings them to their knees.
Right? Or no…
Are you referring to the uEngine demos of DX11 hardware tessellation?
No it was some small developer in the midwest Utah or something. About 3 yrs ago.
Here is a cool link to show what it can do… look at the frog on the bottom with displacement mapping.
http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter07.html
Good for organic stuff.
Wait, no I think you are correct about the Unigine 3D engine. Thought you meant unreal editor at first.
Thats pretty crazy stuff. Like an automated LOD system. I’m sure the normal map would be good enough after the second or third subdiv.
not cheap
Oh lord, $25,000 per project. For the Indie version.
o_o;