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Half-Life has a very limited number of entities to do math operations. They're game_counter and game_counter_set. These entities are very limited by themselves, and Featureful SDK provides more powerful ways to do math operations.

Calc Ratio

All entities have a calculable value associated with them - the concept borrowed from Spirit of Half-Life, where it's called Calc Ratio (see also: Locus system). While most entities have a constant zero value as Calc Ratio, there're few entities that actually implement this concept in Featureful SDK:

• game_counter - the Calc Ratio is the current counter value. Note that game_counter holds integer values only.
• env_global - since each global has an integer number associated with them in Featureful SDK, the env_global can be used to access this number.
• Monsters. For them Calc Ratio is the health / max health fraction (the the number in [0..1] range).
• Wall rechargers (health and armor). For them Calc Ratio is the juice left / max juice capacity fraction (the the number in [0..1] range).
• calc_ratio - Calc Ratio is calculated based on Calc Ratio of another entity.
• calc_eval_number - see calc_eval_number.
• game_number - Calc Ratio is a stored floating point value.
• player_calc_ratio - report some player related values like current health, armor and ammo.

Locus Ratio

Locus Ratio (or LR for short) is a type of entity parameter. In FGD file they're marked with [LR] suffix. LR parameter can be either a constant number or a name of another entity. In the latter case the Calc Ratio result of another entity will be used as a number. The entity that have LR parameters can behave differently depending on their values.

Some examples of entities having LR parameters:

• trigger_push - can have a speed factor calculable from another entity.
• env_shooter - can have a speed factor calculable from another entity.
• calc_ratio - calculates its own Calc Ratio depending on LR parameter.
• Vector related calc entities (e.g. calc_subvelocity) have LR parameter for factor.
• calc_eval_number - see calc_eval_number.
• trigger_compare - when triggered, compares calculated values of two LR parameters and fire the targets accordingly to result.

calc_eval_number

This entity calculates a result of binary operation on two LR parameters.

calc_eval_number can act as LR parameter of another entity by itself. In this case the result of operation is used as Calc Ratio. The calc_eval_number entity can be used as one of operands for another calc_eval_number entity, allowing to do calculations on more than two operands.

When calc_eval_number is triggered by something else it can store the result of operation in other entity (see below).

Storing a value

There're few entities that can act as value storage for the result of calc_eval_number.

• game_counter - the stored value will be cast to integer. The counter may fire its target and reset if it hit the limit.
• game_number - the stored value will be preserved as is. This entity just stores the value and it's expected to be accessed by other entities.
• env_global with Modify/Set value trigger mode. The value will be cast to integer.