RemoteCompose Expression Engine

The Expression Engine allows the Player to perform mathematical calculations and logic locally, enabling smooth animations and responsive UI without constant communication with the host.

RPN (Reverse Polish Notation)

Expressions are encoded using RPN, where operands precede their operators. This allows for efficient stack-based evaluation on the player.

Example: (A + B) * 2

In RemoteCompose, this is represented as: [A_ID, B_ID, ADD, 2.0, MUL]

Evaluation Logic

1. Dependencies: Each expression tracks which variables it depends on.
2. Dirty Tracking: When a variable (like Time or TouchX) changes, all dependent expressions are marked "dirty".
3. Stack Evaluator: AnimatedFloatExpression.eval() iterates through the RPN array:
   • Values are pushed onto a stack.
   • Operators pop their operands from the stack and push the result back.

Supported Operators

Type	Operators
Arithmetic	ADD, SUB, MUL, DIV, MOD, POW
Trigonometry	SIN, COS, TAN, ASIN, ACOS, ATAN, ATAN2
Logic	EQ, NEQ, GT, GE, LT, LE, AND, OR, IFELSE
Special	ABS, MIN, MAX, CLAMP, RAND, PINGPONG, SQUARE, SQRT
System	VAR1, VAR2 (Used in loops and path expressions)

Variable Storage

• RemoteContext: Holds the current value of every float ID in the document.
• Global Variables: System-provided values updated by the player:
  • WINDOW_WIDTH, WINDOW_HEIGHT
  • ANIMATION_TIME, CONTINUOUS_SEC
  • TOUCH_X, TOUCH_Y, TOUCH_PRESSED
  • ACCELEROMETER_X, Y, Z