Immersive Backpacks

Mod authors can add Immersive Backpacks support by marking their bag items as valid side-slot items and providing left/right variants.

The left-side variant can usually be the normal item. The right-side variant should be a separate mirrored technical item so the model can face the correct direction.

Add this to the item’s attributes:

"immersiveBackpacksAllowedSideSlot": true,
"immersiveBackpacksSideSlotVariants": {
	"leftPrefix": "yourmod:yourbag",
	"rightPrefix": "yourmod:yourbag-right"
}

leftPrefix is the item code prefix used in the left side slot.

rightPrefix is the item code prefix used in the right side slot.

Immersive Backpacks converts between these prefixes when an item is moved into the left or right side slot. Any suffix after the prefix is preserved.

For example:

yourmod:yourbag-red        -> yourmod:yourbag-right-red
yourmod:yourbag-blue       -> yourmod:yourbag-right-blue

Stack attributes are preserved during conversion, so bag contents should carry over as long as both variants use compatible held-bag or backpack behavior.

The left-side item should use the left attachment category:

"wearableAttachment": true,
"attachableToEntity": {
	"categoryCode": "leftpack",
	"attachedShape": {
		"base": "yourmod:item/bag/yourbag-attached-left"
	}
}

The right-side technical item should use the right attachment category:

"wearableAttachment": true,
"attachableToEntity": {
	"categoryCode": "rightpack",
	"attachedShape": {
		"base": "yourmod:item/bag/yourbag-attached-right"
	}
}

Right-side technical items should be hidden from the handbook, recipes, loot tables, and traders unless players are meant to obtain them directly.

Recommended: 

"handbook": {
	"exclude": true
}

Slot behavior:

slot 0 = left side bag
slot 1 = normal back slot
slot 2 = right side bag
slot 3 = hidden/unused safety slot. items placed here will be ejected.

Example vanilla-left to right-side mappings used by this mod:

game:basket-*          -> immersivebackpacks:basket-right-*
game:hunterbackpack    -> immersivebackpacks:hunterbackpack-right
game:linensack         -> immersivebackpacks:linensack-right
game:miningbag         -> immersivebackpacks:miningbag-right
game:miningbagsturdy   -> immersivebackpacks:miningbagsturdy-right
game:quiver            -> immersivebackpacks:quiver-right

Left and right variants can use the same base texture files, but their shape texture keys should be separate, or else the left-side technical item's textures will leak into the right.

For example, a normal left-side basket shape might use the texture key basket:

"textures": {
	"basket": {
		"base": "game:item/bag/basket/reed"
	}
}

while the mirrored right-side basket shape might use the texture key basketright:

"textures": {
	"basketright": {
		"base": "game:item/bag/basket/reed"
	}
}

In the case of the basket, without these differentiated texture keys a player with a reed basket in the left slot and a papyrus basket in the right would notice them both having reed basket textures.

The important rule is that the texture key referenced inside the shape file must match the key provided by the itemtype or shape texture map.

For example, if the right-side shape references #basketright, then the right-side itemtype or shape texture map must provide a basketright texture key. That key can still point to the same base texture file as the left-side item. It is just the key that must be different.

For items with multiple variants, such as reed and papyrus baskets, the left and right item codes should preserve the same suffix:

game:basket-normal-reed      -> immersivebackpacks:basket-right-normal-reed
game:basket-normal-papyrus   -> immersivebackpacks:basket-right-normal-papyrus

This lets each right-side variant keep the correct material texture while using a mirrored right-side model.

If you want any further help attempting to add side-slot support that the above documentation doesn't suffice, click the Homepage link at the top to come to my personal modding Discord server, I'd be happy to help you out!