Document not implemented code and basic implementations needing enhancement

docs/development-status.md

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+# Development Status Summary
+
+This document provides a quick overview of RACEngine implementation status and points to detailed documentation.
+
+## Current Implementation Status
+
+### ✅ Well Implemented
+- **Core ECS System** - Entity Component System with comprehensive architecture
+- **Configuration Management** - Robust configuration system with builders
+- **Asset Management** - File system and asset loading with builder pattern
+- **Rendering Pipeline** - Basic OpenGL renderer with multi-phase architecture
+- **Audio System** - Basic audio mixer and service implementation
+- **Input System** - Input service with null object pattern
+- **Dependency Injection** - Consistent DI patterns throughout
+
+### ⚠️ Basic Implementation (Needs Enhancement)
+- **Physics System** - Basic physics with many advanced features marked as NotImplementedException
+- **Camera System** - Basic camera functionality, could expand with advanced controllers
+- **Shader System** - Structure exists but needs shader effects and hot-reload
+- **Project Tools** - GUI application framework exists (Avalonia-based)
+
+### ❌ Not Implemented (Complete Stubs)
+- **Tools Module** - Build pipeline, shader editor, level editor (all TODO stubs)
+- **Animation Module** - Skeletal animation, blend trees (all TODO stubs)
+- **AI Module** - Behavior trees, pathfinding (all TODO stubs)
+- **Networking Module** - All networking functionality (all TODO stubs)
+- **Scripting Module** - Lua and C# scripting engines (all TODO stubs)
+- **Advanced Rendering** - Particle systems, advanced shaders, text rendering
+
+## Quick Statistics
+
+- **Total Files with TODO/NotImplementedException**: 35
+- **Complete Stub Classes**: ~25
+- **Modules with Partial Implementation**: 8
+- **Modules Fully Stubbed**: 5
+
+## For Detailed Analysis
+
+See [Not Implemented Features](development/not-implemented-features.md) for:
+- Complete categorized list of missing functionality
+- Priority recommendations for implementation
+- Enhancement opportunities for existing code
+- Educational value assessment
+
+## For Contributors
+
+The codebase provides excellent learning opportunities with:
+- **Clear Architecture** - Well-documented design patterns
+- **Educational Comments** - Extensive explanations of concepts
+- **Progressive Complexity** - Multiple access layers for different skill levels
+- **Consistent Patterns** - Builder pattern, null object pattern, dependency injection
+
+Students and contributors can choose implementation tasks based on:
+- **Skill Level** - From basic stubs to complex system enhancements  
+- **Interest Area** - Graphics, AI, networking, tools, etc.
+- **Time Commitment** - From simple features to major subsystems
+
+*Last Updated: Based on analysis performed for issue #161*

docs/development/not-implemented-features.md

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+# Not Implemented Features and Code Analysis
+
+This document provides a comprehensive list of functions, classes, projects, and features that are currently not implemented or have only basic implementations that need more work in the RACEngine project.
+
+## Document Purpose
+
+This analysis identifies:
+1. **Complete Stubs**: Classes/interfaces with TODO comments and no implementation
+2. **Basic Implementations**: Features with minimal functionality that need enhancement
+3. **Null Pattern Implementations**: Null object patterns that could provide real functionality
+4. **NotImplementedException Areas**: Features explicitly marked as not implemented
+
+---
+
+## Complete Stubs (TODO Only)
+
+### Tools Module (`Rac.Tools`)
+All tool classes are complete stubs with only TODO comments:
+
+- **`Builder.cs`** - Build pipeline functionality for project compilation and packaging
+- **`ShaderEditorApp.cs`** - Shader editing application
+- **`EditorUI.cs`** - Editor user interface components
+- **`LevelEditorApp.cs`** - Level/scene editor application
+
+### Animation Module (`Rac.Animation`)
+Core animation system components are stubs:
+
+- **`SkeletalAnimator.cs`** - Skeletal animation system
+- **`BlendTree.cs`** - Animation blending and transitions
+- **`IAnimationPlayer.cs`** - Animation playback interface
+
+### AI Module (`Rac.AI`)
+Artificial intelligence features are placeholders:
+
+- **`BehaviorTree.cs`** - AI behavior tree implementation
+- **`IBehaviorTree.cs`** - Behavior tree interface
+- **`IPathfinder.cs`** - Pathfinding interface
+- **`AStarPathfinder.cs`** - A* pathfinding algorithm implementation
+
+### Networking Module (`Rac.Networking`)
+All networking functionality is stubbed:
+
+- **`INetworkClient.cs`** - Network client interface
+- **`LobbyManager.cs`** - Multiplayer lobby management
+- **`ENetClient.cs`** - ENet networking client implementation
+- **`ReplicationSystem.cs`** - Network replication system
+
+### Scripting Module (`Rac.Scripting`)
+Scripting engine support is not implemented:
+
+- **`LuaScriptEngine.cs`** - Lua scripting integration
+- **`CSharpScriptEngine.cs`** - C# scripting support
+- **`IScriptEngine.cs`** - Scripting engine interface
+
+### Rendering Subsystems
+Graphics subsystems needing implementation:
+
+- **`ParticleSystem.cs`** - Particle effects system
+- **`Mesh.cs`** - 3D mesh representation
+- **`IMesh.cs`** - Mesh interface
+- **`ImGuiRenderer.cs`** - ImGui integration for debug UI
+- **`TextRenderer.cs`** - Text rendering system
+- **`RenderPassBase.cs`** - Render pass base class
+- **`IShader.cs`** - Shader interface
+- **`Shader.cs`** - Shader implementation
+- **`ShaderLoader.cs`** - Shader loading and compilation
+
+### Core Infrastructure
+Core engine features not implemented:
+
+- **`TaskScheduler.cs`** - Task scheduling and execution management
+- **`ITaskScheduler.cs`** - Task scheduler interface
+- **`InputMappings.cs`** - Input mapping configuration
+- **`IEntity.cs`** - Entity interface for ECS
+
+---
+
+## NotImplementedException Areas
+
+### Physics Module (`Rac.Physics`)
+The physics builder has multiple NotImplementedException for advanced features:
+
+**Gravity Types** (`PhysicsBuilder.cs`):
+- `GravityType.Realistic` - Real-world gravity simulation
+- `GravityType.Planetary` - Planetary gravity systems
+
+**Collision Types**:
+- `CollisionType.Bepu` - Bepu physics integration
+- `CollisionType.Custom` - Custom collision implementations
+
+**Fluid Simulation**:
+- `FluidType.LinearDrag` - Linear drag simulation
+- `FluidType.QuadraticDrag` - Quadratic drag simulation  
+- `FluidType.Water` - Water physics simulation
+- `FluidType.Air` - Air/atmosphere simulation
+
+---
+
+## Basic Implementations Needing Enhancement
+
+### Audio System (`Rac.Audio`)
+**Implemented**: Basic components exist
+**Needs Work**:
+- **`AudioMixer.cs`** - Has volume control but could expand with:
+  - Dynamic range compression
+  - Real-time audio effects (reverb, echo, filters)
+  - 3D spatial audio positioning
+  - Audio streaming for large files
+  - Cross-fade transitions between tracks
+
+- **`Sound.cs`** - Basic sound representation, could add:
+  - Sound pooling for performance
+  - Compressed audio format support
+  - Looping and playback control enhancements
+  - Audio visualization data
+
+### Asset System (`Rac.Assets`)
+**Implemented**: File system and builder pattern
+**Needs Work**:
+- **`AssetServiceBuilder.cs`** - Has comprehensive builder but missing:
+  - Cache configuration API implementation (line 310: TODO comment)
+  - Async loading capabilities
+  - Hot-reload/asset streaming
+  - Asset dependency tracking
+  - Compression and optimization pipelines
+
+### Rendering System (`Rac.Rendering`)
+**Implemented**: Core OpenGL renderer and pipeline
+**Needs Work**:
+- **Multiple shader implementations** - Basic structure exists but need:
+  - Advanced shader effects (PBR, post-processing)
+  - Shader hot-reload for development
+  - Compute shader support
+  - Multi-pass rendering techniques
+
+- **Camera system** - Basic implementation could expand with:
+  - Advanced camera controllers (FPS, orbit, cinematic)
+  - Camera animation and transitions
+  - Multi-camera rendering setups
+
+### ECS System (`Rac.ECS`)
+**Implemented**: Core ECS functionality
+**Needs Work**:
+- **System scheduling** - Basic systems exist but could add:
+  - Multi-threaded system execution
+  - System dependency resolution optimization
+  - Performance profiling and monitoring
+  - Dynamic system loading/unloading
+
+---
+
+## Null Pattern Implementations (Expansion Opportunities)
+
+These null implementations provide safe fallbacks but could be enhanced with optional functionality:
+
+### Input System
+- **`NullInputService.cs`** - Could add:
+  - Input recording/playback for testing
+  - Input validation and sanitization
+  - Debug input visualization
+
+### Rendering
+- **`NullRenderer.cs`** - Could add:
+  - Render command logging for debugging
+  - Performance metrics collection
+  - Headless rendering to textures/files
+
+### Physics
+- **`NullPhysicsService.cs`** - Could add:
+  - Physics state validation
+  - Collision detection debugging
+  - Physics recording for analysis
+
+### ECS Infrastructure
+- **`NullQueryBuilder.cs`** - Could add query validation
+- **`NullQueryRoot.cs`** - Could add query performance logging
+- **`NullWorld.cs`** - Could add entity state tracking
+- **`NullContainerService.cs`** - Could add dependency injection logging
+
+---
+
+## Priority Recommendations
+
+### High Priority (Core Engine Functionality)
+1. **Task Scheduler** - Critical for engine loop and system coordination
+2. **Shader System** - Essential for any visual rendering
+3. **Input Mappings** - Required for user interaction
+4. **Entity Interface** - Fundamental to ECS architecture
+
+### Medium Priority (Feature Completeness)
+1. **Animation System** - Important for dynamic content
+2. **Particle System** - Common in games, good for visual polish
+3. **Text Rendering** - Essential for UI and debugging
+4. **Asset Cache Configuration** - Performance optimization
+
+### Low Priority (Advanced Features)
+1. **Advanced Physics** - Can use basic physics initially
+2. **Scripting Engines** - Nice-to-have for modding
+3. **Networking** - Important for multiplayer but not core engine
+4. **Tools** - Development productivity but not runtime critical
+
+### Enhancement Opportunities (Existing Code)
+1. **Audio Effects** - Expand mixer with real-time effects
+2. **Shader Hot-Reload** - Development productivity feature
+3. **Multi-threaded Systems** - Performance optimization
+4. **Null Implementation Logging** - Development and debugging aid
+
+---
+
+## Implementation Patterns Observed
+
+### Well-Implemented Areas
+- **Configuration Management** - Comprehensive and well-documented
+- **Dependency Injection** - Consistent pattern usage
+- **Builder Pattern** - Extensive use with fluent APIs
+- **Documentation** - Excellent XML comments and educational content
+
+### Areas for Pattern Consistency
+- **Error Handling** - Some areas use exceptions, others return defaults
+- **Async Operations** - Inconsistent async/await usage
+- **Validation** - Some builders have comprehensive validation, others minimal
+- **Logging** - Inconsistent logging patterns across modules
+
+---
+
+## Educational Value Assessment
+
+This codebase demonstrates excellent educational practices:
+- **Comprehensive Documentation** - Each class explains patterns and concepts
+- **Academic References** - Mentions specific algorithms and papers
+- **Design Pattern Usage** - Clear examples of common patterns
+- **Progressive Complexity** - Multiple access layers for different skill levels
+
+The not-implemented areas provide excellent opportunities for:
+- **Learning Implementation** - Students can implement missing features
+- **Design Pattern Practice** - Following established patterns in the codebase
+- **Performance Optimization** - Opportunities to optimize basic implementations
+- **Architecture Understanding** - See how features fit into overall engine design
+
+---
+
+*This document will be updated as features are implemented or new areas requiring implementation are identified.*