Add helper functions and comments.

Signed-off-by: Curtis Black <[email protected]>

src/include/OSL/oslconfig.h.in

@@ -231,6 +231,19 @@ ustringrep_from(string_view s)
 
 
 
+using TypeDesc_pod = long long;
+
+
+
+/// Convenience function to convert to a TypeDesc.
+inline TypeDesc
+TypeDesc_from(TypeDesc_pod type)
+{
+    return OSL::bitcast<OSL::TypeDesc>(type);
+}
+
+
+
 // N.B. SymArena is not really "configuration", but we cram it here for
 // lack of a better home.
 

src/include/OSL/rendererservices.h

@@ -34,9 +34,9 @@ enum class AttributeSpecBuiltinArg {
     ShaderGlobalsPointer,  // void* (TODO: ideally ShaderGlobals*)
     ShadeIndex,            // int
     Derivatives,           // bool
-    Type,                  // long long (TODO: ideally TypeDesc)
+    Type,                  // TypeDesc_pod
     ArrayIndex,            // int, Always zero for non-indexed array lookups.
-    ArrayLookup,           //bool
+    ArrayLookup,           // bool
     ObjectName,            // const char* (TODO: change to ustringhash)
     AttributeName,         // const char* (TODO: change to ustringhash)
 };
@@ -451,6 +451,7 @@ class OSLEXECPUBLIC RendererServices {
                                   TypeDesc::VECSEMANTICS vectype);
 
     /// @brief Builds a free function to provide a value for a given attribute.
+    /// This occurs at shader compile time, not at execution time.
     /// @param group The shader group currently requesting the attribute.
     /// @param object_lookup True if an object name was specified, even if the
     /// value is not known at compile time.

src/testshade/rs_simplerend.cpp

@@ -257,15 +257,19 @@ rs_get_attribute_constant_float4(float value1, float value2, float value3,
 
 OSL_RSOP bool
 rs_get_attribute(void* _sg, const char* _object, const char* _name,
-                 long long _type, bool derivatives, int index, void* result)
+                 OSL::TypeDesc_pod _type, bool derivatives, int index,
+                 void* result)
 {
     OSL::ShaderGlobals* sg        = reinterpret_cast<OSL::ShaderGlobals*>(_sg);
     const OSL::StringParam object = OSL::bitcast<OSL::ustringrep>(_object);
     const OSL::StringParam name   = OSL::bitcast<OSL::ustringrep>(_name);
-    const OSL::TypeDesc type      = OSL::bitcast<OSL::TypeDesc>(_type);
+    const OSL::TypeDesc type      = OSL::TypeDesc_from(_type);
 
     const RenderState* rs = reinterpret_cast<RenderState*>(sg->renderstate);
 
+    // The many branches in the code below handle the case where we don't know
+    // the attribute name at compile time. In the case it is known, dead-code
+    // elimination should optimize this to only the relevant branch.
     if (name == "osl:version" && type == OSL::TypeInt)
         return rs_get_attribute_constant_int(OSL_VERSION, result);
     if (name == "camera:resolution"