There seems to be a problem with gutter space in the unwrap algorythm. I’ve not noticed it so far, but with my last project, it became really apparent. Some texture areas seem to be too close so that with lower resolution the gutter space cannot be maintained and there will be bleeding (see screenshots).
I’ve tried it with gutter 2 and 4, different texel size and legacy algorythm. The problem is always identical. I’ve marked one of the areas in Blender to vizualize the problem better. In an “inlet” of one surface (cyan), which is not strictly logical, there is another small area (yellow) which is really a bit further behind the first one. This area is nested in this inlet in the UV (screenshot bottom), where you can see that the distance is almost 0 in some areas.
When I increase the gutter space in the unwrap settings, then the texture usage will increase, which means that in general there is more gutter, but as I said in this case the distance remains exactly the same.
I sent the project files to support for investigation.
After a lot of trial and error I managed to work around the problem by modifying the UV map using Blender.
It is quite a bit of effort and it takes too much time fixing everything, but the most obvious parts can be “repaired” by that. Most time consuming is finding the spots in the first place, especially with high poly models as I use them.
The good thing (for me) is that I learned a lot about unwrapping, which is surprisingly difficult for models approaching and exceeding 1M tris, which I wasn’t aware of before.
Bearing that in mind, I am now convinced that apart from the described issue, the algorythm used by RC is doing an amazing job, both in terms of quality and speed. This insight led to a feature request: