[HLSL] define the matrix element accessor semantics

specs/language/expressions.tex

@@ -153,6 +153,7 @@
   typename-specifier braced-init-list\br
   postfix-expression \terminal{.} \opt{\terminal{template}} id-expression\br
   postfix-expression \terminal{.} vector-swizzle-component-sequence\br
+  postfix-expression \terminal{.} matrix-swizzle-component-sequence\br
   postfix-expression \terminal{++}\br
   postfix-expression \terminal{--}
 \end{grammar}
@@ -173,7 +174,19 @@
 elements in the vector, the program is ill-formed. If the value is outside the
 range at runtime, the behavior is undefined.
 
-\Sec{Vector Swizzle}{Expr.Post.VectorSwizzle}
+\Sec{Swizzle}{Expr.Post.Swizzle}
+\p A \textit{postfix-expression} followed by a dot (\texttt{.}) and a sequence
+of one or more \textit{swizzle-components} is a postfix expression. The
+postfix expression before the dot is evaluated and must be of vector or matrix type.
+If the postfix expression before the dot is an lvalue, the swizzle expression may
+produce either an lvalue or a prvalue; otherwise it produces a prvalue.
+
+
+\p If the postfix expression before the dot is
+an lvalue and the \textit{swizzle-component-sequence} contains no repeated
+components, the swizzle expression is an lvalue; otherwise it is a prvalue.
+
+\Sec{Vector Swizzle}{Expr.Post.Swizzle.Vector}
 
 \begin{grammar}
   \define{vector-swizzle-component-sequence}\br
@@ -195,23 +208,14 @@
   \terminal{x y z w}
 \end{grammar}
 
-\p A \textit{postfix-expression} followed by a dot (\texttt{.}) and a sequence
-of one or more \textit{swizzle-components} is a postfix expression. The
-postfix expression before the dot is evaluated and must be of vector type. If
-the postfix expression before the dot is an lvalue, the swizzle expression may
-produce either an lvalue or a prvalue; otherwise it produces a prvalue.
-
-\p A \textit{swizzle-component-sequence} is a sequence of one or more swizzle
+\p A \textit{vector-swizzle-component-sequence} is a sequence of one or more swizzle
 components of either the \textit{swizzle-component-rgba} or
 \textit{swizzle-component-xyzw} forms; the two forms may not be mixed in the
-same \textit{swizzle-component-sequence}. The type of a swizzle expression is a
+same \textit{vector-swizzle-component-sequence}. The type of a swizzle expression is a
 vector of the same element type as the postfix expression before the dot, with a
-number of elements equal to the number of components in the
-\textit{swizzle-component-sequence}. If the postfix expression before the dot is
-an lvalue and the \textit{swizzle-component-sequence} contains no repeated
-components, the swizzle expression is an lvalue; otherwise it is a prvalue.
+number of elements equal to the number of components in the \textit{vector-swizzle-component-sequence}. 
 
-\p Swizzle components map to elements of the vector in the following way:
+\p Vector swizzle components map to elements of the vector in the following way:
 
 \begin{center}
   \begin{tabular}{|| c | c | c ||}
@@ -230,6 +234,46 @@
 refers to an element index that is out of range of the vector type of the
 postfix expression before the dot.
 
+\Sec{Matrix Swizzle}{Expr.Post.Swizzle.Matrix}
+\begin{grammar}
+  \define{matrix-swizzle-component-sequence}\br
+  matrix-zero-indexed-swizzle-sequence\br
+  matrix-one-indexed-swizzle-sequence\br
+
+  \define{matrix-zero-indexed-swizzle-sequence}\br
+  matrix-zero-indexed-swizzle\br
+  matrix-zero-indexed-swizzle-sequence matrix-zero-indexed-swizzle\br
+
+  \define{matrix-zero-indexed-swizzle}\br
+  \terminal{\_m} zero-index-value\br
+
+  \define{zero-index-value} \textnormal{one of}\br
+  \terminal{0 1 2 3 }\br
+
+  \define{matrix-one-indexed-swizzle-sequence}\br
+  matrix-one-indexed-swizzle\br
+  matrix-one-indexed-swizzle-sequence matrix-one-indexed-swizzle\br
+
+  \define{matrix-one-indexed-swizzle}\br
+  \terminal{\_m} one-index-value\br
+
+  \define{one-index-value} \textnormal{one of}\br
+  \terminal{1 2 3 4 }\br
+\end{grammar}
+\begin{itemize}
+\item \textbf{.\_} (math-style): subsequent subscripts use \textbf{1-based}
+ indexing for both row and column.
+\item \textbf{.\_m} (memory-style): subsequent subscripts use \textbf{0-based}
+ indexing for both row and column.
+\end{itemize}
+
+\p A \textit{matrix-swizzle-component-sequence} is a sequence of one or more swizzle
+components of either the \textit{matrix-zero-indexed-swizzle} or
+\textit{matrix-one-indexed-swizzle} forms; the two forms may not be mixed in the
+same \textit{matrix-swizzle-component-sequence}. The type of a swizzle expression is a
+vector of the same element type as the postfix expression before the dot, with a
+number of elements equal to the number of components in the \textit{matrix-swizzle-component-sequence}.
+
 \Sec{Function Calls}{Expr.Post.Call}
 
 \p A function call may be an \textit{ordinary function}, or a \textit{member