#5 - fixed interpolation & rollback

modules/serialization/include/tw/serial/WorldStateWriter.hpp

@@ -23,7 +23,7 @@ class WorldStateWriter {
 public:
     explicit WorldStateWriter(BinaryBuffer& buf) noexcept : m_w(buf) {}
 
-    void begin(uint32_t frame_idx, uint32_t message_type) noexcept {
+    void begin(uint32_t frame_idx, uint32_t tick_idx, uint32_t message_type) noexcept {
         m_entity_count = 0;
 
         // message_type — lets the receiver dispatch without peeking further
@@ -35,6 +35,10 @@ public:
         // frame_idx
         m_w.encode<uint32_t>(frame_idx);
 
+        // tick_idx — counts the states that went out, so the receiver can tell
+        // a late one from a new one. Says nothing about the frame answered.
+        m_w.encode<uint32_t>(tick_idx);
+
         // entity_count placeholder — patched when end() is called
         m_entity_count_offset = m_w.reserve_u32();
     }
@@ -85,6 +89,7 @@ public:
 struct WorldStateHeader {
     uint32_t packet_type;
     uint32_t frame_idx;
+    uint32_t tick_idx;
     uint32_t entity_count;
 };
 
@@ -109,10 +114,11 @@ public:
     explicit WorldStateReader(std::span<const std::byte> data) noexcept
         : m_r(data) {}
 
-    /** Read the 12-byte header. Must be called first. */
+    /** Read the header. Must be called first. */
     WorldStateHeader read_header() noexcept {
         // m_header.packet_type  = m_r.decode<uint32_t>();
         m_header.frame_idx    = m_r.decode<uint32_t>();
+        m_header.tick_idx     = m_r.decode<uint32_t>();
         m_header.entity_count = m_r.decode<uint32_t>();
 
         // spawn count follows immediately