Conditional Gcode Syntax Spec

- DRAFT -

Contents on this page are proposed and may not be implemented.

These features are planned for all custom G-Code fields.

The Slic3r Manual contains everything that has been implemented: http://manual.slic3r.org/advanced/conditional-gcode

Related Feature Request/Issue: https://github.com/alexrj/Slic3r/issues/3390

All Slic3r variables referenced must be known by PlaceholderParser (eg [])

Conditional expressions

Conditional expressions has the following syntax:

• {if expression}

expression may take one of the following forms:

• VARIABLE OPERATOR CONSTANT
• CONSTANT OPERATOR VARIABLE
• {subexpression} OPERATOR {subexpression}
• OPERATOR subexpression

subexpression has the same forms as expression.

If _subexpression_s exist, they are evaluated before any other operators.

Available operators:

• && or and - logical AND
• || or or - logical OR
• ! or not - logical NOT (inversion)
• ^ or xor - XOR (exclusive-OR)
• == or equals - equality comparison.
• != - inequality comparison. To use words, use a subexpression.
• < - less than (valid for numbers only)
• <= - less than or equal to (valid for numbers only)
• > - greater than (valid for numbers only)
• >= - greater than or equal to (valid for numbers only)

Available keywords:

• 'false'
• 'true'

To apply a single condition to multiple lines, repeat it once for each line.

{if [layer_num] == 10}M104 S210
{if [layer_num] == 10}M600

• If a conditional expression evaluates to false, all the characters until the end of the line are removed.
• If a conditional expression fails to parse, it's left in place with the {} removed..
• Expressions may be chained for an implicit AND.

{if [layer_num] == 10}{if [temperature_1] != 210}M104 S210

Conventions

• Numerical value of 0 is equivalent to logical false. Any nonzero value is considered to be logical true.
  • {if { 1 - 1 } } would result in 0 and thus false.

Comments

Outside of an expression { and } may be escaped with a single \.

Value expressions

Any expression enclosed in two curly brackets, but not starting with {if is evaluated as an arithmetic expression: {foo - bar}. If evaluation fails, the expression is silently left untouched with the enclosing {} removed. If any float variables are used, return value will have decimals. If string variables are mixed with numeric variables, they are parsed as floats if they have a dot, or integers otherwise.

Additional available operators:

• + - Addition
• - - Subtraction
• / - Division
• * - Multiplication

Value expressions can be used in conditional expressions by nesting them: {if {foo - bar} > 10}.

Comments

Should we also support modulo division and/or power syntax? I can see a couple use cases for modulo, but not for power - @lordofhyphens