1.3.9.4 What is a condition and how do I make one?

A condition is an expression that evaluates to a boolean value (ie. true or false) and is used in POV-Ray in #while-loops and #if-statements.

A condition is mainly a comparison between two values (although there are also some other ways of making a condition, but that is not important now). For example:

1 < 2  is true
1 > 2  is false
1 = 1  is true
1 = 2  is false

and so on.

Usually it makes no sense to make comparisons like those. However, when comparing identifiers with some value or two identifiers together it starts to be very useful. Consider this:

#if(version < 3.1)
  #error "Wrong version!"
#end

If the identifier called 'version' has a value which is less than 3.1 the #error line will be executed. If 'version' has a value which is 3.1 or greater, the #error line is just skipped.

You can combine conditions together with the boolean operators & (and) and | (or). You can also invert the value of a condition with ! (not).

For example, if you want something to be done when 'a' is less than 10 and 'b' is greater or equal to 20, the condition would be:

a<10 & b>=20

For more information about these comparison operators, see the 'Float operators' section of the POV-Ray documentation.