Bot skillset modding

This wiki page explains the skilltree as of https://github.com/Unvanquished/Unvanquished/pull/2635.

Basic principle

An example of skilltree structure

Each skill is a boolean on/off tag, that has some chance of being unlocked. As long as there are skill points to spend, the next skill is selected randomly.

Visualising the skilltree

There are two commands, /devbotcountskillpoints and /devbotgraphskilltree [skillLevel] that can help handling the skilltree.

The first command, /devbotcountskillpoints, just prints a message with the total cost of (reachable) skills in the tree for each team. This can help figuring out the maximum budget want.

Here's an advanced example where the buy-modern-armor skill is a base-skill (always enabled) and the prefer-armor skill is disabled (never selected randomly)

The second command, /devbotgraphskilltree [skillLevel] saves a .dot graph file that can be converted to an image. For example one can do this in the game console:

/devbotgraphskilltree 5
game/bot-skilltree-alien.dot written 
game/bot-skilltree-human.dot written 

Then (e.g.) this in a terminal:

$ dot -Tpng ~/.local/share/unvanquished/game/bot-skilltree-human.dot > result.png && xdg-open result.png

If one gives the skill level as an argument argument to the /devbotgraphskilltree command, it will print the statistics for that skill level, with colors for the disabled and forced skills.

Modifying and tweaking the skilltree

Depending on your objectives, which maybe to offer diverse and interesting bots e.g. for a juggernaut mod, or to provide very predictable bots e.g. for a tournament, you may have different desire for bot customisations. The current implementation of the skilltree should be flexible enough to allow this.

The skill selection process is customised by these cvars:

• g_skillset_baseSkills which set the initial skills for the various skill levels.
• g_skillset_budgetHumans and g_skillset_budgetAliens
• g_skillset_disabledSkills, which will prevent skills from being randomly selected.

Skilltree in pure random "mode"

You sometime want to have maximum randomness in your opponents, with a purely random skill setup. For example this can make PvE games or Juggernaut fights more interesting.

You can do that by:

• setting the g_skillset_baseSkills cvar to an empty string
• giving some skill funds for your bots to randomly choose from, using the g_skillset_budgetHumans and g_skillset_budgetAliens cvars.

In the current implementation, you get floor(budget*(2+skillLevel)/9) skill points to spend so that the whole budget is unlocked at skill level 7 while keeping a reasonable amount of points at lower skills. The code for this is in src/sgame/sg_bot_skilltree.cpp, in BotPickSkillset's definition of skill_points.

Skilltree in pure deterministic "mode"

You sometime want purely deterministic bots, for example for tournaments or for easier inital balancing. This is the way I'd like Unvanquished to go towards on the long term.

If you wish to have perfectly identical bots for some skill levels, you can set g_skillset_budgetHumans and g_skillset_budgetAliens to 0 and write the g_skillset_baseSkills list.

Skilltree in mixed "mode"

There is a third way, where one can define "vital" skills that have to be selected for given skill levels. You can do this by setting the base skills are always selected, and give more budget than those initial skills cost, so that the leftover skill points (if any) will be used randomly.

You can do that by

• setting the g_skillset_baseSkills cvar to the base required skills for each level, then
• giving some extra skill funds for your bots to randomly choose from, using the g_skillset_budgetHumans and g_skillset_budgetAliens cvars.

💡️ Tip: You can even have some skills mandatory at some skill levels and forbidden from the other skill levels. To do that, you add the skill in the g_skillset_disabledSkills list AND in g_skillset_baseSkills for your desired skill threshold. This will exclude a skill from the random selection but still allow the budget to select the other skills. This works because the base skill list takes precedence.

The visualisation features explained in #Visualising_the_skilltree will be very useful in this situation, make sure you know how to use them.