Removed static variables

[najlkin]

Refactored code to remove static variables from VisualizationScenes, which are fine in the native app when declared as thread_local (not always the case), but fail in glvis-js, where a new instance of visualization scene is started (in the same window and thread). Initialization does not happen again and the values are carried over.
Bonus: Changed key handlers and variables to private.

[camierjs]

Thank you @najlkin, neat!

[ragnar-howler]

Code Review: Removed static variables

Summary

This PR addresses an important architectural issue where static variables with thread_local work correctly in the native app but fail in glvis-js, where new visualization scene instances are started in the same window/thread without reinitialization.

Changes Analysis

1. Static Member Migration (Good)

• Moving vsdata, vssol, vssol3d, vsvector, vsvector3d from global statics to static thread_local class members is proper encapsulation
• Thread safety is preserved - thread_local ensures per-thread isolation

2. Key Handler Refactoring (Good)

• Converting free functions to static member functions improves code organization
• Making them private hides implementation details from public API
• All key handlers properly access scene instance via the static thread_local pointer

3. Instance Variable Fixes (Critical Fix)

Moving these from static globals to instance variables correctly fixes state carryover:

• magic_key_pressed (vssolution3d)
• ianim, ianimmax, key_u_func (vsvector)
• arrows_nl, vector_h, vector_hh (vsvector3d - replaces static locals)

This ensures each scene instance maintains its own state.

4. Plane Constructor Change

// Before:
Plane(double A, double B, double C, double D);
// After:
Plane(const double (&eqn_)[4], const VisualizationScene::Box &bb);

• Passing bounding box by reference avoids accessing global state
• Array reference for equation parameters is cleaner
• The named struct Box in openglvis.hpp enables this

5. Logic Corrections

• vsvector.cpp: ChangeDisplacement() correctly handles wraparound with modulo arithmetic
• vsvector3d.cpp: ArrowsDrawOrNot() now uses arrows_nl member (initialized to -1) instead of first_time static
• KeyrPressed/KeyRPressed now correctly use vsvector3d-> instead of window->vs->

Verdict

✅ Approve

This is a well-executed refactoring that:

• Fixes the glvis-js state carryover bug
• Improves encapsulation
• Maintains thread safety
• Preserves all existing functionality

The changes are minimal and focused on the specific issue without unnecessary scope creep.