I have a 3D model, which is separated peice by peice.
When I load it up, it appears as normal.
But I thought I could improve the rendering performance by merging those into one
so that I’ve merged those into one and load it up then the normal gets broken.
And I found that there’s no significant performance improvement although I’ve merged those into one
What can be the problem here?
You’ve just established that what you changed was not your main bottleneck.
I suggest you always profile first. Then optimize. That reduces the amount of time/effort/code spent reworking things that often won’t net you any gains.