In Brogue's source code, "magic polarity" refers to the property of an item which determines whether it will display an benevolent magic (positive polarity), aura of malevolent magic (negative polarity), or no aura of magic (−neutral polarity). The magic polarity of an item is revealed when detect magic is used.
Identifying an item will not reveal its polarity, although the player will likely be able to deduce it from the item's type, cursed status, and enchantment level.
Among roguelike players, equipment that is generated with positive enchantment levels is often referred to as "blessed", although there is technically no such status in Brogue.
Determining magic polarity
The game determines the magic polarity of an item by the following rules.
- For potions, scrolls, and staves, the polarity / is determined by the item type: potions that harm the drinker are negative, scrolls that are bad for the reader are negative. Staves that make the target more powerful are negative.
- For wands, the polarity functions similarly to staves, with the exception that a wand becomes −neutral when it is out of charges. While charged, wands that make the target more powerful are negative, and other wands positive.
- For equipment that is cursed, the magic polarity is always negative.
- For equipment that is not cursed, the magic polarity is determined by enchantment level. A -3 item is negative, a +0 item is −neutral, and so on.
- Runics have no direct effect on polarity. Runic items are always generated with non-zero enchantment levels which determine their starting polarity: positive runics only occur on items with positive enchantment levels, and negative runics only occur on cursed items with negative enchanment levels.
- Charms and amulets are always positive.
- Mundane items that cannot be enchanted, such as food, are always −neutral.
Effects of revealing magic polarity
- After an item's polarity has been revealed, it will be marked with a symbol on the inventory screen. Positive polarity is shown as a filled blue symbol , negative as an empty red symbol , and neutral as a yellow dash −.
- Similarly, the symbol will show up on the map, except for neutral items. Positive and negative items within the level are sensed telepathically. This telepathic link persists even after picking up or dropping the item. For example, if a monkey steals a potion which you have detected magic on, you will be able to track the monkey's movements by sensing the item's location.
- Drinking a potion or reading a scroll that is known to have a negative polarity will ask the player "Really drink/read a [item]?"
Changing an item's magic polarity
- Enchanting a −neutral item (a +0 equipment or a spent wand) raises its enchantment level to a positive number, and thus changes its polarity to positive.
- Equipment that is corroded by acid has its enchantment level decremented by 1. Thus, a regular sword that is corroded to -1 will appear as having negative magic polarity.
- Removing the curse from equipment and enchanting it up to +0 will change it to −neutral. Enchanting it to +1 or higher will change it again to positive. Thus, even equipment with a negative runic can appear to be non-malevolent, if sufficiently enchanted (though there is no good reason for a player to do so).
- Using up a wand's charges changes it from its normal polarity / to −neutral.
Function "itemMagicPolarity", Items.c, lines 6941-6998. BrogueCE. Revision c13cb1d on Nov 29, 2020. https://github.com/tmewett/BrogueCE/blob/d3fd46fb3f291f9abb397880b36735f78c36fc90/src/brogue/Items.c#L6937-L6998