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

Expression Controller

This controller evaluates a user written expression, and gives a positive (TRUE) output when

The result of the expression is TRUE, and

The object is in the designated State.

For all other conditions the controller gives a negative (FALSE) output.

Expression Controller

Expression

The expression, which is written in the box, can consist of variables, constants and operators. These must follow the rules laid out below.

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.