Expressions

Expressions in Pix define conditions over the coordinate variables x and y. They are evaluated for every pixel position on the grid to determine which pixels should be drawn.

Coordinate variables

x is the horizontal position (increases rightward from 0) and y is the vertical position (increases downward from 0). These are the only variables available in expressions.

Operator precedence

From lowest to highest:

Arithmetic operators

These operate on numbers and produce numbers. All arithmetic uses signed 64-bit integers.

x + 5       // addition
x - 8       // subtraction (can produce negative values)
2 * x       // multiplication
x / 2       // integer division (truncates toward zero)
x ^ 2       // exponentiation (right-associative)

Division by zero and negative exponents produce errors.

Comparison operators

Comparisons take two numbers and return a boolean.

x = 3       // equal
x < 5       // less than
x > 0       // greater than
x <= 5      // less than or equal
x >= 0      // greater than or equal

Logical operators

Logical operators combine boolean values.

x = 3 and y = 5           // both must be true
x = 0 or y = 0            // either can be true
not (x = 0)                // negation

Parentheses

Use parentheses to group sub-expressions and override precedence.

(x - 8) ^ 2 + (y - 8) ^ 2 < 16   // circle equation
(x > 5 and y < 10) or (x = 0)     // grouped logic

Type rules

Operators require specific types. There is no implicit type coercion.

The condition in a draw or erase statement must evaluate to a boolean. Using a number expression as a condition produces an error.