A reference message is sent from a target to reference makers which maintain a direct reference (either strong or weak) to it. A reference message is represented by the type RefMessage. Reference messages are sent by a reference target in response to a call to ReferenceTarget::NotifyDependents(). The message is received by an observing reference maker in the method ReferenceMaker::NotifyRefChanged(). A plug-in will override this method to process messages received from any scene objects that it observes and depends on.

Reference messages are integer constants defined in the file ref.h. A full list of reference messages can be found in the topic Reference Messages in the 3ds Max SDK reference guide.

Some of the most common reference messages follow:

• REFMSG_TARGET_DELETED - This message is sent when a ReferenceTarget is deleted.
• REFMSG_CHANGE - Sent to dependents of a ReferenceTarget that has changed in some way.
• REFMSG_BEGIN_EDIT - This is used by modifiers to indicate when they are beginning an edit.
• REFMSG_END_EDIT - This is used by modifiers to indicate when they are ending an edit.
• REFMSG_MOD_EVAL - Modifier uses this to tell modified objects to call their Object::Eval() procedure.

User defined reference messages should be defined as a value greater than REFMSG_USER. For example.

const RefMessage MYMSG1 = REFMSG + 0;
const RefMessage MYMSG2 = REFMSG + 1;
// ...