Acuity Library 1.12.2 is a core mod with an API modders can use to implement multi-layered textures, emissive rendering and fancy visual effects (shaders) for block rendering with good performance on moderate to high-end hardware, all without using TileEntitySpecialRenderer. This mod is client-side only and can be quickly enabled and disabled at run time via configuration settings. When the mod is disabled, the game uses normal Minecraft rendering.
Baseline vanilla forge render performance with complex terrain and 16-chunk render distance. After all chunks are loaded, FPS is around 70/second.
Same scene rendered with Acuity enabled. After all chunks are loaded, FPS is around 80/second. Note there is a defect here: Acuity renders slightly darker.
Massive lava flows rendered with a custom pipeline.