evennia/docs/source/Contribs/Crafting.md

Crafting system contrib

Contrib by Griatch 2020

This contrib implements a full Crafting system that can be expanded and modified to fit your game.

• See the evennia/contrib/crafting/crafting.py API for installation instructrions.
• See the sword example for an example of how to design a crafting tree for crafting a sword from base elements.

From in-game it uses the new craft command:

> craft bread from flour, eggs, salt, water, yeast using oven, roller
> craft bandage from cloth using scissors

The syntax is craft <recipe> [from <ingredient>,...][ using <tool>,...].

The above example uses the bread recipe and requires flour, eggs, salt, water and yeast objects to be in your inventory. These will be consumed as part of crafting (baking) the bread.

The oven and roller are "tools" that can be either in your inventory or in your current location (you are not carrying an oven around with you after all). Tools are not consumed in the crafting. If the added ingredients/tools matches the requirements of the recipe, a new bread object will appear in the crafter's inventory.

If you wanted, you could also picture recipes without any consumables:

> craft fireball using wand, spellbook

With a little creativity, the 'recipe' concept could be adopted to all sorts of things, like puzzles or magic systems.

In code, you can craft using the evennia.contrib.crafting.crafting.craft function:

from evennia.contrib.crafting.crafting import craft

result = craft(caller, "recipename", *inputs)

Here, caller is the one doing the crafting and *inputs is any combination of consumables and/or tool Objects. The system will identify which is which by the Tags on them (see below) The result is always a list.

Adding new recipes

A recipe is a class inheriting from evennia.contrib.crafting.crafting.CraftingRecipe. This class implements the most common form of crafting - that using in-game objects. Each recipe is a separate class which gets initialized with the consumables/tools you provide.

For the craft command to find your custom recipes, you need to tell Evennia where they are. Add a new line to your mygame/server/conf/settings.py file, with a list to any new modules with recipe classes.

CRAFT_RECIPE_MODULES = ["world.myrecipes"]

(You need to reload after adding this). All global-level classes in these modules (whose names don't start with underscore) are considered by the system as viable recipes.

Here we assume you created mygame/world/myrecipes.py to match the above example setting:

# in mygame/world/myrecipes.py

from evennia.contrib.crafting.crafting import CraftingRecipe

class WoodenPuppetRecipe(CraftingRecipe):
    """A puppet""""
    name = "wooden puppet"  # name to refer to this recipe as
    tool_tags = ["knife"]
    consumable_tags = ["wood"]
    output_prototypes = [
        {"key": "A carved wooden doll",
         "typeclass": "typeclasses.objects.decorations.Toys",
         "desc": "A small carved doll"}
    ]

This specifies which tags to look for in the inputs. It defines a Prototype for the recipe to use to spawn the result on the fly (a recipe could spawn more than one result if needed). Instead of specifying the full prototype-dict, you could also just provide a list of prototype_keys to existing prototypes you have.

After reloading the server, this recipe would now be available to use. To try it we should create materials and tools to insert into the recipe.

The recipe analyzes inputs, looking for Tags with specific tag-categories. The tag-category used can be set per-recipe using the (.consumable_tag_category and .tool_tag_category respectively). The defaults are crafting_material and crafting_tool. For the puppet we need one object with the wood tag and another with the knife tag:

from evennia import create_object

knife = create_object(key="Hobby knife", tags=[("knife", "crafting_tool")])
wood = create_object(key="Piece of wood", tags[("wood", "crafting_material")])

Note that the objects can have any name, all that matters is the tag/tag-category. This means if a "bayonet" also had the "knife" crafting tag, it could also be used to carve a puppet. This is also potentially interesting for use in puzzles and to allow users to experiment and find alternatives to know ingredients.

By the way, there is also a simple shortcut for doing this:

tools, consumables = WoodenPuppetRecipe.seed()

The seed class-method will create simple dummy objects that fulfills the recipe's requirements. This is great for testing.

Assuming these objects were put in our inventory, we could now craft using the in-game command:

> craft wooden puppet from wood using hobby knife

In code we would do

from evennia.contrub.crafting.crafting import craft
puppet = craft(crafter, "wooden puppet", knife, wood)

In the call to craft, the order of knife and wood doesn't matter - the recipe will sort out which is which based on their tags.

Deeper customization of recipes

For customizing recipes further, it helps to understand how to use the recipe-class directly:

class MyRecipe(CraftingRecipe):
    # ...

tools, consumables = MyRecipe.seed()
recipe = MyRecipe(crafter, *(tools + consumables))
result = recipe.craft()

This is useful for testing and allows you to use the class directly without adding it to a module in settings.CRAFTING_RECIPE_MODULES.

Even without modifying more than the class properties, there are a lot of options to set on the CraftingRecipe class. Easiest is to refer to the CraftingRecipe api documentation. For example, you can customize the validation-error messages, decide if the ingredients have to be exactly right, if a failure still consumes the ingredients or not, and much more.

For even more control you can override hooks in your own class:

• pre_craft - this should handle input validation and store its data in .validated_consumables and validated_tools respectively. On error, this reports the error to the crafter and raises the CraftingValidationError.
• craft - this will only be called if pre_craft finished without an exception. This should return the result of the crafting, by spawnging the prototypes. Or the empty list if crafting fails for some reason. This is the place to add skill-checks or random chance if you need it for your game.
• post_craft - this receives the result from craft and handles error messages and also deletes any consumables as needed. It may also modify the result before returning it.
• msg - this is a wrapper for self.crafter.msg and should be used to send messages to the crafter. Centralizing this means you can also easily modify the sending style in one place later.

The class constructor (and the craft access function) takes optional **kwargs. These are passed into each crafting hook. These are unused by default but could be used to customize things per-call.

Skilled crafters

What the crafting system does not have out of the box is a 'skill' system - the notion of being able to fail the craft if you are not skilled enough. Just how skills work is game-dependent, so to add this you need to make your own recipe parent class and have your recipes inherit from this.

from random import randint
from evennia.contrib.crafting.crafting import CraftingRecipe

class SkillRecipe(CraftingRecipe):
   """A recipe that considers skill"""

    difficulty = 20

    def craft(self, **kwargs):
        """The input is ok. Determine if crafting succeeds"""

        # this is set at initialization
        crafter = self.crafte

        # let's assume the skill is stored directly on the crafter
        # - the skill is 0..100.
        crafting_skill = crafter.db.skill_crafting
        # roll for success:
        if randint(1, 100) <= (crafting_skill - self.difficulty):
            # all is good, craft away
            return super().craft()
        else:
            self.msg("You are not good enough to craft this. Better luck next time!")
            return []

In this example we introduce a .difficulty for the recipe and makes a 'dice roll' to see if we succed. We would of course make this a lot more immersive and detailed in a full game. In principle you could customize each recipe just the way you want it, but you could also inherit from a central parent like this to cut down on work.

The sword recipe example module also shows an example of a random skill-check being implemented in a parent and then inherited for multiple use.

Even more customization

If you want to build something even more custom (maybe using different input types of validation logic) you could also look at the CraftingRecipe parent class CraftingRecipeBase. It implements just the minimum needed to be a recipe and for big changes you may be better off starting from this rather than the more opinionated CraftingRecipe.