Currently I'm working on a mod which includes a lot of complex block models, and some of them may be greater than a normal cube size, so I decided to use code to generate BakedQuads.

Those blocks just look fine when they are placed into the world or held inside the inventory, but once they are dropped into the world (become EntityItem) and held in hand, weird things start to happen.

As shown in the attached picture, the EntityItem model is too dark and lighting is not working properly.

Can anyone suggest what could go wrong? Thanks in advance!

 

PS: If I return true in isGui3D() in the IBakedModel, the inventory model becomes dark too (sad QAQ!!!

Check the vertex format of the baked quads you are generating. Item rendering requires normals for correct lighting and so you need to generate quads with ITEM vertex format that include proper normals. Quads in item format can also be used for block rendering if you don't need lightmaps.