From ef1ee63f03c5b79ccc267533bac77d5a49c478a1 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Fri, 11 Jul 2008 17:46:30 +0000
Subject: [PATCH] From Joakim Simmonson, "Opcodes.h: * Added INVALID_OP as -1
 in the Opcodes enum. Note that INVALID_OP is not an actual opcode defined in
 the OpenFlight format. The purpose of INVALID_OP is to mark an opcode
 variable as invalid or uninitialized.

ReaderWriterFLT.cpp:
* The header node is returned if it exists, even if the file does not contain a node hierarchy. The old behaviour returned a ERROR_IN_READING_FILE error.
* Changed opcodes initialized to -1 to the new enum value INVALID_OP."
---
 src/osgPlugins/OpenFlight/Opcodes.h           |  4 ++++
 src/osgPlugins/OpenFlight/ReaderWriterFLT.cpp | 21 +++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/osgPlugins/OpenFlight/Opcodes.h b/src/osgPlugins/OpenFlight/Opcodes.h
index 510e69814..8304341d3 100644
--- a/src/osgPlugins/OpenFlight/Opcodes.h
+++ b/src/osgPlugins/OpenFlight/Opcodes.h
@@ -22,8 +22,12 @@
 
 namespace flt {
 
+
+// Note that INVALID_OP = -1 is not an actual opcode defined in the OpenFlight format.
+// The purpose of INVALID_OP is to mark an opcode variable as invalid or uninitialized.
 enum Opcodes
 {
+    INVALID_OP                          = -1,
     UNKNOWN_OP                          = 0,
     HEADER_OP                           = 1,
     GROUP_OP                            = 2,
diff --git a/src/osgPlugins/OpenFlight/ReaderWriterFLT.cpp b/src/osgPlugins/OpenFlight/ReaderWriterFLT.cpp
index e01235882..01372fed1 100644
--- a/src/osgPlugins/OpenFlight/ReaderWriterFLT.cpp
+++ b/src/osgPlugins/OpenFlight/ReaderWriterFLT.cpp
@@ -86,7 +86,7 @@ public:
 
 /*!
 
-FLTReaderWriter supports importing and exporting OSG scene grqphs
+FLTReaderWriter supports importing and exporting OSG scene graphs
 from/to OpenFlight files.
 
 <table>
@@ -284,7 +284,7 @@ class FLTReaderWriter : public ReaderWriter
             }
 
             const int RECORD_HEADER_SIZE = 4;
-            opcode_type continuationOpcode = -1;
+            opcode_type continuationOpcode = INVALID_OP;
             std::string continuationBuffer;
 
             while (fin.good() && !document.done())
@@ -299,8 +299,21 @@ class FLTReaderWriter : public ReaderWriter
                 opcode_type opcode = (opcode_type)dataStream.readUInt16();
                 size_type   size   = (size_type)dataStream.readUInt16();
 
+                // If size == 0, an EOF has probably been reached, i.e. there is nothing 
+                // more to read so we must return.
                 if (size==0)
-                    return ReadResult::ERROR_IN_READING_FILE;
+                {
+                    // If a header was read, we return it.
+                    // This allows us handle files with empty hierarchies.
+                    if (document.getHeaderNode())
+                    {
+                        return document.getHeaderNode();
+                    }
+                    else // (no valid header)
+                    {
+                        return ReadResult::ERROR_IN_READING_FILE;
+                    }
+                }
 
                 // variable length record complete?
                 if (!continuationBuffer.empty() && opcode!=CONTINUATION_OP)
@@ -310,7 +323,7 @@ class FLTReaderWriter : public ReaderWriter
                     flt::RecordInputStream recordStream(&sb);
                     recordStream.readRecordBody(continuationOpcode, continuationBuffer.length(), document);
 
-                    continuationOpcode = -1;
+                    continuationOpcode = INVALID_OP;
                     continuationBuffer.clear();
                 }