Understanding the Problem

Scene Graph Corruption and Runtime Instability

The C4 Engine uses a scene graph structure for spatial and renderable object organization. Runtime instability or access violations often stem from invalid node references, improper deletion order, or misuse of base class pointers when extending engine objects.

Why It Matters in Enterprise or Simulation Use Cases

In non-game applications such as military simulations, architectural walkthroughs, or digital twins, crashes due to scene graph traversal failures can cause downtime, data loss, or incorrect visualization outputs—introducing serious liability risks.

Architectural Overview of the C4 Scene Graph

Core Hierarchy: Node → GeometryNode → ShapeNode

The scene graph in C4 Engine is built upon a strict inheritance model where each node has parent and sibling relationships. Nodes are updated recursively each frame through the Preprocess() and Move() functions.

Lifecycle and Memory Ownership

Mismanagement of lifecycle—especially between the world manager and individual plugin systems—can result in accessing freed memory or double deletions when the world is torn down or reloaded dynamically.

Root Causes of Node Corruption

1. Manual Pointer Management in Custom Classes

Developers often subclass GeometryNode or Effect classes but forget to properly call base destructors or orphan node children in Dispose() methods.

2. Incorrect Use of Handles

C4 provides a handle-based system to manage references. Improper detachment before node deletion leads to dangling handles or race conditions when scene updates happen on other threads.

3. Asynchronous Scene Graph Modification

Attempting to modify the scene graph (e.g., removing or adding nodes) from a thread other than the main simulation thread can result in mid-frame inconsistencies and render pipeline failure.

Diagnostics and Debugging

Enabling Memory Guarding

Use C4::MemoryMgr::EnableGuardZones(true) during debug builds. This enables buffer overrun detection and logs underflows at deletion time.

Tracking Scene Graph Mutations

Instrument custom nodes to log creation, addition, and deletion:

LogMessage("Node Created: %s", GetNodeName());
LogMessage("Node Added to Parent: %s", parent->GetNodeName());
LogMessage("Node Disposed: %s", GetNodeName());

Stack Trace on Crash with Custom Signal Handler

#include 
void CrashHandler(int sig) { DumpStackTrace(); exit(1); }
int main() { signal(SIGSEGV, CrashHandler); InitC4(); }

Step-by-Step Fixes

1. Audit All Custom Node Subclasses

Ensure Dispose() methods are implemented properly and call Node::Dispose() to remove children and detach from parent.

2. Use Handles, Not Raw Pointers

Refactor custom systems to replace raw pointers with NodeHandle or ObjectHandle to ensure safe dereferencing and auto-nullification on deletion.

3. Enforce Main-Thread Scene Graph Mutations

Schedule node modifications via event messages or the C4 command queue. Never alter the scene graph during render or physics update phases from auxiliary threads.

4. Use WorldMgr Hooks for Consistency

Leverage WorldMgr::AddWorldObserver() to track world lifecycle events and delay deletion until WorldEnding() is called.

5. Profile Scene Graph Performance

Use built-in performance graphs (press F4 in dev builds) and log Preprocess() time per node to detect slow or recursive loops that may indicate logic bugs.

Best Practices

- Always use New() and Delete() macros provided by the engine for allocation/deallocation - Avoid deleting nodes mid-frame; schedule them at frame end - Limit scene graph depth to reduce recursive traversal overhead - Use the debugger visual scene hierarchy (F7) for orphan detection - Implement a static analysis pass to detect improper subclassing patterns

Conclusion

Debugging C4 Engine scene graph instability requires a deep understanding of its node lifecycle, memory management rules, and threading constraints. By using safe handle-based references, properly implementing custom class destructors, and enforcing main-thread-only updates, development teams can eliminate hard-to-reproduce crashes and deliver stable, high-performance 3D applications built with C4.

FAQs

1. Why does my custom node crash during world teardown?

It likely holds references to deleted child nodes or fails to detach properly in Dispose(). Always call the base Dispose() and clean up handles.

2. Can I safely delete nodes from another thread?

No. Scene graph is not thread-safe. Use deferred execution or message passing to modify it on the main thread only.

3. What's the difference between NodeHandle and ObjectHandle?

NodeHandle is for scene graph objects; ObjectHandle is for general engine objects like materials or effects. Both ensure safe dereferencing post-deletion.

4. How do I find orphan nodes?

Use the F7 developer scene inspector or log parent-child relationships during creation. Orphans typically lack a valid parent or are detached mid-frame.

5. Is there a memory leak detection tool built into C4?

Yes. Use EnableMemoryReport() before exiting the app to log active allocations and leaks in the debug console.