Recipe Categories

A recipe category defines everything that's common across entire categories of recipes.

The recipe categories add by plugins in JEI are Crafting, Smelting, Fuel, Brewing, and Description.
See VanillaRecipeCraftingUid for more information about these recipe categories.

Responsibilities of a recipe category:

Define a category

The category's UID
Localized Title
Background Image

Set recipe layouts based on the given recipe wrapper.

Fill out which ingredients are visible on the screen and their location.

Optional Abilities of a recipe category:

Draw extra elements and animations on the screen.

Some categories may need to draw extra slots or other elements not drawn by the background.

Implementation

Fill out the required methods for the UID and Title.

Defining the Background and other images

There are helpful methods in IGuiHelper for drawing cropped resources on the screen.
The way the recipe lays out on the screen depends on the background's size.

The less height the background has, the more recipes fit on one screen.
Backgrounds may need extra padding to fit text without running into the next recipe.
Be sure to check how your recipe looks at different GUI scales in Minecraft. JEI will try to display more recipes when the GUI scale is smaller.

Setting the recipe layout

For a better understanding of this process, follow along with one of the IRecipeCategory implementations in the List of Plugin Implementations.

In IRecipeCategory.setRecipe, the category will define the layout of ingredients for a single IRecipeWrapper. The IRecipeLayout is set up here to display ingredients, that each have tooltips and can be clicked to navigate to other recipes.

From the IRecipeLayout, get the ItemStack, FluidStack, or other IGuiIngredientGroup that you want to place.
Init the IGuiIngredientGroup with the locations the ingredients should be drawn.
Set the ingredients in the IGuiIngredientGroup using the various set methods.