The RenderMan Interface - Paul Bourke

Section 13
LANGUAGE CONSTRUCTS
13.1 Expressions
Expressions are built from arithmetic operators, function calls, and variables. The language
supports the common arithmetic operators (+, -, *, and /) plus the vector operators ˆ (cross
product) and . (dot product), and the C conditional expression (binary relation expr1 :
expr2).
When operating on points, vectors, normals, or colors, an arithmetic operation is performed
in parallel on each component. If a binary operator involves a float and a multicomponent
type (such as a point, vector, normal, matrix, or color), the float is promoted to
the appropriate type by duplicating its value into each component. It is illegal to perform
a binary operation between a point and a color. Cross products only apply to vectors; dot
products apply to both vectors and colors. Two points, two colors, or two strings can be
compared using == and !=. Points cannot be compared to colors.
The usual common-sense mathematical rules apply to point/vector/normal arithmetic.
For example, a vector added to a point yields a point, a vector added to a vector yields a
vector, and a point subtracted from a point yields a vector. Mixing the types of vectors,
normals, and points (for example, taking a cross product of two points, rather than two
vectors) is allowed, but is discouraged. A particular implementation may choose to issue
a compiler warning in such cases. Note that vectors and normals may be used nearly
interchangably in arithmetic expressions, but care should be taken to distinguish between
them when performing coordinate system transformations.
Matrix variables can be tested for equality and inequality with the == and != boolean operators.
The * operator between matrices denotes matrix multiplication, while m1 / m2
denotes multiplying m1 by the inverse of matrix m2. Thus, a matrix can be inverted by
writing 1/m.
13.2 Standard Control Flow Constructs
The basic explicit control flow constructs are:
• block-structured statement grouping,
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