Couldn't be further than GW's.
GW's code is black box and can only be viewed under license.
GPUO-if it transpires as claimed appears to be not only modifiable but more importantly open to optimisation, GW's isn't.
GW code can be viewed under license, which is an industry norm.
Even if the GPUO code is made publicly available without license it is is fairly irrelevant to the developers that choose GW.
Developers don't at all mind a black box, in fact it is preferable The entire point is the developers don't have the resources to develop the feature themselves, and the last thing they want to be doing is poking around with other peoples code. They want a plug and play solution with rock solid support -that is what Nvidia aims to rpovide. If a GW feature is not working well or is missing a feature that a developer wants then the developers approaches Nvidia and Nvidia resolves the issue.
When making the Witcher 3 the developers wanted lots of changes to hairworks, Nvidia made the changes in the library and so now every developer gets to take advantage of those improvements.
with AMD"s approach if a developer makes improvements then depending on the license 1 or 2 things happens: 1) the developer gets to keep the improvement secret so only they get the advantage, 2) alternatively they are forced to shared the change with the whole and push the code changes to the git repository. Neither scenario is particularly appealing for most developers, not least they really don't want to be spending time making changes, they want a plug and play solution.
IF any developer really want to get their hands dirty they are far more likely to simply code the entire effect themselves and forget GW or GPUO.
Lasltly, Nvidia's model has advantages because the game code makes calls to an external API which can be updated by nvidia without the game developer having to make future game patches. For example, lets say pascal comes around with a new feature that makes doing a certain effect much faster if coded in a slightly different way. If a games is release din say summer 2015 and pascal in June 2016, Nvidia can have a launch day update to games-works that exploits the increased capability of Pascal with the changes done in the GW library. The old game form last summer now automatically get the boost in performance without the developer having to do a thing. With the GPUO approach the game would remain completely unchanged and wont be able to take advantage of new hardware unless the developer go back to coding and put in the resources themselves in to making improvements, which is as likely as pigs flying .
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