There is hardly any reason for us to recalculate everything all the time. LUTs can cache the work once, and then re-use it every time necessary, drastically reducing the impact of Color Grading by almost 60% (on some GPUs even more). Additionally this fixes the negative gamma issue, which plagued the filter for a while.
In the future, once PR 4199 (https://github.com/obsproject/obs-studio/pull/4199) has been merged, we can cut away one intermediate rendering step currently required to make the effect work. Hopefully this will be with the 27.x release of OBS Studio.
