Doc:2.6/Manual/Game Engine/Logic/Controllers/Expressions

Game Expressions

A controller can evaluate an expression in order to send a positive or negative pulse to the connected actuators:

• if the expression evaluates to True, the controller sends a positive pulse to the connected actuators.
• if the expression evaluates to False, the controller sends a negative pulse to the connected actuators.

Variables

You can use:

• sensors names,
• properties: assign a game property to an object and use it in a controller expression.

These cannot contain blank spaces.

Operations

Mathematical operations

Operators: *, /, +, -

Returns: a number

Examples: 3 + 2, 35 / 5

Logical operations

• Comparison operators: <, >, >=, <=, ==, !=
• Booleans operators: AND, OR, NOT

Returns: True or False.

Examples: 3 > 2 (True), 1 AND 0 (False)

Conditional statement (if)

Use:

if( expression, pulse_if_expression_is_true, pulse_if_expression_is_false )

If the controller evaluates expression to True:

• if pulse_if_expression_is_true is True, the controller sends a positive pulse to the connected actuators.
• if pulse_if_expression_is_true is False, the controller sends a negative pulse to the connected actuators.

If the controller evaluates expression to False:

• if pulse_if_expression_is_false is True, the controller sends a positive pulse to the connected actuators.
• if pulse_if_expression_is_false is False, the controller sends a negative pulse to the connected actuators.

Examples

Given the object has a property coins equal to 30:

coins > 20

returns True (the controller sends a positive pulse to the connected actuators).

Given the object has:

• a sensor called Key_Inserted equal to True,
• a property named Fuel equal to False,

Key_Inserted AND Fuel

returns False (the controller sends a negative pulse to the connected actuators).

This is the same as doing:

if (Key_Inserted AND Fuel, True, False)

Instead, you could do:

if (Key_Inserted AND Fuel, False, True)

to return a positive pulse when Key_Inserted AND Fuel returns False.

You can also do:

if ((Key_Inserted AND Fuel) OR (coins > 20), True, False)

This expression returns True, hence in this case the controller sends a positive pulse to the connected actuators.