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Contents 1 Introduction 2 New RIB Commands 3 Conditions 4 New C Commands

[edit] Introduction

Conditional RIB allows a single rib file to be reused in multiple renders with different settings. For example, you might choose to set options or attributes conditionally, or to swap shaders.

This is most often combined with user attributes.

For example:

Option "user" "string mode" "bake"
#Option "user" "string mode" "read"

IfBegin "$Option:user:mode == 'bake'"
  Attribute "dice" "rasterorient" 0
  Attribute "cull" "backfacing" 0
  Attribute "cull" "hidden" 0
  Surface "bakingShader"
Else
  Suface "readingShader"
IfEnd

[edit] New RIB Commands

IfBegin "<expression>"

All command until either ElseIf, Else or End will only be executed if "<condition>" evaluates to true.

Else

Commands until End will be executed if "<condition>" did not evaluate to true.

ElseIf "<condition>"

Allows complex conditions to be built up.

End

Ends conditional RIB evaluation.

Conditions may be nested.

[edit] Conditions

Conditions can take the following form:

$variable

look up an attribute or option

* / + -

float or integer aritmetic

(<expr>)

evaluate a subexpression

==  != < <= >= >

evaluate comparison between two expressions, strings may be compared with == or !=

&& || !

boolean operation on subexpressions (as in C)

'string literal'

a string constant expression

123

a number constant

defined(variable)

is an option or attribute defined

concat(expr1,expr2)

concatenate two string subexpressions

$(expr)

look up a variable who'se name is the result of the string expression expr

Options may be looked up with $Option:<optionname>, and attributes with $Attribute:<attributename>. User options and attributes are therefore $Option:user:<optionname> and $Attribute:user:<optionname> respectively.

[edit] New C Commands

Conditional RIB is also available via the C Ri Interface (in ri.h):

RtVoid RiIfBegin(char *expr, ...),
RtVoid RiIfBeginV(char *expr, RtInt n, RtToken tokens[], RtPointer parms[]),
RtVoid RiElseIf(char *expr, ...),
RtVoid RiElseIfV(char *expr, RtInt n, RtToken tokens[], RtPointer parms[]),
RtVoid RiElse(void),
RtVoid RiIfEnd(void);