Good news for RHM users, and even better news for VR users who need all the CPU cycles they can salvage:
(copy/paste from the AC Custom Shaders Discord, courtesy of Insert Coin):
WallyM has adapted the original AC Real Head Motion for ACC and fixed the high CPU usage of the plugin too. I have had contact with WallyM and asked if he could fix the high CPU usage for the original AC version of the plugin too. This was his reply: "So I just discovered that RHM for ACC also works for AC. Look behind is a bit screwy, but you don't use that (in VR) anyway. If you want to have separate settings for ACC and AC, just set up two different RHM folders - one for AC and one for ACC. They will each have their own settings that way." I have tested his ACC version of the RHM plugin on AC and it works. CPU usage was reduced on my i7 CPU (4 core, 8 threads) from 4.2% on average for the original AC RHM plugin to 0.6% for the new plugin. The original plugin kept hogging the CPU even when AC wasn't running, the new plugin stays at 0% as it should. Recommended for VR users, since they need every CPU cycle they can get. The new RHM plugin can be downloaded here: https://www.assettocorsa.net/forum/index.php?threads/real-head-motion-for-acc-is-here.63606/
It seems you can also rename the ACC RHM executable to RealHeadMotionAssettoCorsa.exe which allows CM integration for auto-launching.
