Isnt a static GI really just good old precomputed light maps? There are more tricks up their sleeve to render lighting in each scene, but it really isn't Global Illumination in a true sense if its prebaked/precalced and not dynamically adjusting for ray sourced global lighting.
GI is the new buzzword so every publisher is claiming their engine does their own flavor of it to hit that bullet point, but very few actual do in the strict sense. Unreal started this stuff when they dropped SVOGI for a more advanced lightmap solution, and others are now following lead.
As far as I can tell from what's been said Unity also dropped their GI implementation for traditional lightmaps on steroids as well, because in the end they got just about the same visual features without the huge performance cost and only really sacrificed a day/night cycle.
I guess its all semantics, but its just strange to me that proven old tech with advances is being rebranded.
Well here is how the tricks go. I will try to explain as much simple as I can. I will need to bring some examples from UE4 that I did and I will use UE4 examples to explain this once and for all. In fact Lightmaps and shadowmaps have been used for a long time now in many engines to mimic the effects of global illumination. Here is how they do it. They use a static source of light which gives as result lit surfaces with indirect lights and lit ones with indirect lights and the resulting shadows. This light and shadow data can be stored in UV textures called lightmaps and shadowmaps and can be applied on surfaces and meshes' textures to give the impression of being lit. This has been done in almost every game from that last generation with old engines to make it run on low end machines (this has bene done even in Cryengine 2 with Crysis 2 and many UE3 games and so). Since the GI is basically textures, they have to be stored in the game files and disk and will eat more space just like regular textures. I take now the example of UE4 whihc has a a new and advanced ligthing tech compared to old gen. In fact UE4 uses what is called Lightmass. This tech is like a dynamic source of Light but instead it is either static or stationary (for example turning on and off but stayin in teh same position). This method creates indirect lighting from the direct light creating lightmaps and shadowmaps in real time on surfaces and meshes without creating UV lightmaps and shadowmaps that are stored as regular textures that are blended with surfaces and mshes UV textures to give the impression of being lit but instead the light data stays stored in static volumes instead of turning into textures files which saves much space. So let is say that is a semi automatic GI, it is still static but it doesn't involve the artists to store light data within textures. The benefit of such tech :storing the light data in volume instead of textures is that it can make movable meshes like charcters interact with it and get the diffused lights like here in Unity where Arno socks and shirt get lit by red light diffused from the red carpet, so if they were just simple lightmaps and shadowmaps, Arno wouldn't get such detail. Unity must be using sth similar to lightmass. The benefit of such tech is that it takes time to get built and rendred but the result is so accurate and without artefacts or flaws since the source of light is static. sadly this method has one disadvantage when it comes to surfaces and areas that are difficult to reach by light which gets special type of shades (no defined shadow shapes) which is caleld ambient occlusion that defines the edges of most things, that is why an extra effor or tool or program or option ahs to be added to put them in emphasis like here the HBAO+ which just gives approximative results by trying to guess the surfaces which are difficult to reach by the light without having a direct connection to the static light source, that is why it is just an approxiamtion.
yes UE4 dropped SVOGI because it is the most technically advanced algorithm of dynamic GI and it eats a lot of ressources even on highest end PCs. Thye secertly replaced with LPV (light propagation volumes) a very rudimentary way to get dynamic GI.
This technic stores moving light data in that propgates in to those big volumes and tries to diffuse them dynamically. Well you get dynamic GI but the results aren't that accurate. I will show how it goes (using examples I made using UE4). Here is the dynamic GI LPV enabled but the light source (the sun ) is not moving, you get awesome GI results with even blending colours:
http://imgur.com/a/VGQnS
When you make the sun move thus making it a dynamic source of GI, you get colours changing and shadows too (here no lightmaps or shadowmaps stored at all), following the sun postion and day/night cycle you get the same wall getting different colour combination from orange to purple in real time which is very awesome and impressive. You can even get lit characters in real timeby lights switching colours accoridng to the sun position and time: here being lit eitehr by red wall thhen yellow wall and standing in the same position but in different time of the day (different sun position):
http://imgur.com/a/I3spm
So techwise it is very impressive. Sadly this tech is not that accurate when it hits advanced meshes even static ones and you get archaic results not as accurate like in Unity here for example which has static GI:
http://i.imgur.com/qiC6YMe.jpg
And it also
only works with sunlight, directional dynamic light aren't supported in UE4, they only cast direct lights:
http://i.imgur.com/6troVKM.png
A dynamic method of GI doesn't need extra work to mimic the results of ambient Occlusion since the light source is dynamic so it creates dark occlued (hardly reachable by light) surfaces. With LPV, occlued surfaces is horrendous they are very blocky and pixalated and huge and not subtle eventhough they are real time.
I come back to the method Epic dropped aka SVOGI, but let me begin with the method Nvidia are devloping aka VXGI which is Voxel Global Illumation. This method is just like LPV but wayyyy more precise , it almost can reach the accuracy of the static lightmass. While LPV uses big volumes and stores big chunks of diffused lights in one direction per big volume, VXGI stores light information per voxel (cubic piwel) which is very tiny and can propagte light in different directions, now sum all the data colelcted in those tiny voxels and you will get avery accurate approximation of diffused lights
IN REAL TIME. So this can be applied to everything going from moving light sources to emissive materials or textures. You can read about it here and watch videos :
https://developer.nvidia.com/gi-works and here :
http://www.geforce.com/hardware/technology/vxgi/technology and you can download the recently released VXGI UE4 Apollo 11 demo here:
http://blogs.nvidia.com/blog/2014/11/11/maxwell-apollo-demo/
Enlighten is also developing an effective dynamic GI for UE4 with multiple dynamic sources and emissive materails that can interact with static and mocing meshes :
https://forums.unrealengine.com/showthread.php?50658-Geomerics-Enlighten-Finally-supports-UE4
The SVOGI (Sparse Voxel Octree Global Illumination) is even more impressive tech since it uses a sparse voxel octree which can collect light data from voxels from different shapes in an area accessible to the user's eyesight and it can even collect data and render from light sources invsible light sources and display their diffused lights in the field of view of the user. Both VXGI and SVOGI have also dynamic reflections created by dynamic GI sources. Sadly both techs require too much ressources: The Apollo 11 VXGI demo needs at least a GTX 970 card to just render a very simple scene with just 3 meshes and no complex surronding environments. Not only that but both can only have just one bounce per dynamic light source and light only get diffused in few directions per voxel making deeper areas dark and that still needs an external intervention of a method of Ambient Occlusion. Here is an exmaple fo someone who tried to enable two bounces per dynamic GI light in cryengine. (you can download the demo in the description if you have a hefty PC)
https://www.youtube.com/watch?v=8PCnkJBvIrY
As you can notice dynamic reflections created by dynamic GI sources are not accurate and are blocky :
https://forums.unrealengine.com/attachment.php?attachmentid=16047&d=1414981939 and the same blocky real time reflections are noticable on the helmets of the cosmonauts' helmets
https://www.youtube.com/watch?v=RNt5znFLv9Y
And both demos don't uses PBR materials and simple scenes otherwise it would be an overkill.
The only best and accurate instance of dynamic GI is used in The Tomorrow children wihic uses Cascaded Voxel Cone Ray Tracing. This method is very good and gives very gorgeus results. Ok it is not the same method as the SVOGI or VXGI, since both are 100% automatic methods meaning that anyone can throw them on the go and work and can work with anything in th scene from static to dynamic meshes. Q-Games tried SVOGI but they found out it was very slow so they ditched octree hiearchy stores data and to determine distance from the camera to scale voxels and optimize for distance, much like LoD for a new approach aka 3D textures that developers would have to generate the textures, mostly by hand, prior to importing the models or assets into the game. That is why they are using ray-traced generated volumes instead of polygonal models. The advantage of this method is that not only it frees up ressources but it also allows desv to get better results and verty realtsic ones too. Raytraced generated volumes and models are very accurate and you will never find any hard edge like in polygonal meshes that need heavy tesselation to correct the edges. They can now go for 16 diffused light directions per voxel and they can even reach 3 bounces per light direction (even for invisble light sources) which even Pixar movies didn't reach (and the dev confirmed that). Reflections are as accurate as in real life and you won't get blocky reflections. They can even apply 3 types of AA and the list goes one. Ok, their method isn't as impressive as VXGI or SVOGI, ok their GI is still dynamic but it needs extra interventions from the the devs to fill data in each 3D texture and get their own approximations so it means only Q-Games devs cna use it sinc ethey ahve to interact with it, while with VXGI and SVOGI it is automatic and anyone can integrate it on the game by just dropping it in any scene with any object without extra work. So their method is dynamic is dynamic but semi automatic while VXGI and SVOGI is dynamic and automatic, yet Q-games approach has better and more accurate results on screen than SVOGI and VXGI just like I said before that the static GI in Unity looks better than the dynamic GI available now which are more impressive and demanding techwise.
Sadly don't expect any accuarte GI method to work correctly with open world settings with rough reliefs neither from VXGI nor from SVOGI , let alone a full automatic q-games like approach in the near future: maybe for next-gen.
Sorry for making it soooooooo long , but trust me I tried to make is as simple as possible.