Complete roguelike tutorial using C++ and libtcod - part 9: spells and ranged combat

Complete roguelike tutorial using C++ and libtcod -originally written by Jice Text in this tutorial was released under the Creative Commons Attribution-ShareAlike 3.0 Unported and the GNU Free Documentation License (unversioned, with no invariant sections, front-cover texts, or back-cover texts) on 2015-09-21.

part 1: setting up part 2: map and actors part 3: dungeon building part 4: field of view part 5: preparing for combat part 6: going berserk! part 7: the GUI part 8: items and inventory part 9: spells and ranged combat part 10.1: persistence part 10.2: game menu part 11: dungeon levels and character progression extra 1: about editors and IDE extra 2: debugging extra 3: scent tracking extra 4: makefiles extra 5: more generic items

In this article, we'll start to add diversity to the gameplay by adding three new spells :

• lightning bolt : deals damages to the closest enemy
• fireball : powerful area effect spell
• confusion : turns the selected enemy into a randomly wandering zombie for a few turns

The scroll of lightning bolt

This dreadful spell will deal 20 damage to the closest monster, up to a distance of 5 tiles. So the first thing we need is some helper functions to get the closest monster within a range.

Some helpers

The easiest is a function to get the distance from an actor to a specific tile of the map :

Actor.hpp

float getDistance(int cx, int cy) const;

Actor.cpp

float Actor::getDistance(int cx, int cy) const {
   int dx=x-cx;
   int dy=y-cy;
   return sqrtf(dx*dx+dy*dy);
}

Well that was a small warmup. Don't forget to include math.h for the sqrtf function. Now let's do something manlier.

Engine.hpp

Actor *getClosestMonster(int x, int y, float range) const;

This function returns the closest monster from position x,y within range. If range is 0, it's considered infinite. If no monster is found within range, it returns NULL.

Engine.cpp

Actor *Engine::getClosestMonster(int x, int y, float range) const {
   Actor *closest=NULL;
   float bestDistance=1E6f;

First we declare some variable. closest is the closest monster found so far. bestDistance is the distance for the closest monster found so far. We initialize it with a value higher than any possible value (1E6 == 1000000) so that the first monster in the range will be a candidate. So let's iterate over the actors list and check alive monsters :

for (Actor **iterator=actors.begin();
   iterator != actors.end(); iterator++) {
   Actor *actor=*iterator;
   if ( actor != player && actor->destructible 
       && !actor->destructible->isDead() ) {
Now let's check if the guy is within range and closer than what we found so far.

           float distance=actor->getDistance(x,y);
           if ( distance < bestDistance && ( distance <= range || range == 0.0f ) ) {
               bestDistance=distance;
               closest=actor;
           }
       }
   }
   return closest;
}