How It Works

A Bit of History

For a very long time (even before 1.14), Forge was the popular mod loader. sp614x created OptiFine for it, which, in addition to optimization features, added the CIT (Custom Item Textures) system that was ported from MCPatcher. But when players started switching to Fabric, they couldn't use OptiFine due to technical reasons, and thus Fabric players temporarily lost access to CIT. However, in 2021-22, user shsupercm released the CIT Resewn mod for Fabric, which fully restored this functionality.

Later, after the release of 1.21.2, Mojang began actively changing their Minecraft rendering code, and in 1.21.4 they changed the item rendering system. In 1.21.5, vanilla was able to (almost) completely replace the main feature of CIT that people used it for - items by custom names. By this time, shsupercm had already given up and stopped supporting CIT Resewn.

Then some people noticed a problem: in vanilla's resource pack system, if you try to add 2 (or more) packs with the same model, there's an issue. The problem was that Mojang implemented model loading so that only the topmost model is loaded, while others aren't loaded into the game's memory at all.

RPF solves this problem: it rewrites the loading code so that all items from all resource packs are loaded into the game, and adapts the model selection process accordingly.

How the Resolver Works

First, let's define some terms:

• Fallback model - this is a child model of an item, which is specified in the fallback fields in minecraft:select and minecraft:range_dispatch. Typically, unless these are some exceptional cases described here
• Resolver - this is an RPF module that decides which item model to send for rendering based on its own rules

Now to the essence. The standard resolver system (yes, there's more than one! read about this in the Delegation System section) goes through models and their children in order, and if a model does NOT delegate rendering - then we render it!