Reimplement Blender Internal render engine as custom addon

.gitignore

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+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+
+# Blender
+*.blend1
+*.blend2
+*.blend~
+
+# OS
+.DS_Store
+Thumbs.db

BLENDER_INTERNAL_README.md

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+# Blender Internal Render Engine - Reimplementation
+
+## Overview
+
+This addon reimplements the classic **Blender Internal** render engine that was deprecated and removed in Blender 2.8. It provides a basic scanline renderer with support for materials, lighting, and simple shading.
+
+## Features
+
+- **Custom Render Engine**: Fully functional render engine that appears in the render engine dropdown
+- **Material Support**: Basic material rendering with diffuse and specular components
+- **Lighting**: Support for Point lights and Sun lights with energy and color controls
+- **Scanline Rendering**: Simple but effective rasterization algorithm
+- **Camera Support**: Proper perspective projection from camera viewpoint
+- **World Background**: Uses scene world color as background
+
+## Installation
+
+1. Download `blender_internal_render.py`
+2. Open Blender (3.0 or higher recommended)
+3. Go to **Edit > Preferences > Add-ons**
+4. Click **Install** and select the downloaded file
+5. Enable the addon by checking the box next to "Render: Blender Internal Render (Reimplemented)"
+
+## Usage
+
+### Selecting the Render Engine
+
+1. In the Properties panel, go to the **Render Properties** tab (camera icon)
+2. At the top, you'll see **Render Engine** dropdown
+3. Select **Blender Internal** from the list
+
+### Basic Rendering
+
+1. Set up your scene with:
+   - A Camera (required)
+   - Mesh objects
+   - Lights (Point or Sun)
+   - Materials with colors
+
+2. Press **F12** to render or click **Render > Render Image**
+
+### Supported Features
+
+#### Materials
+- The addon extracts base color from materials
+- Works with both node-based materials (Principled BSDF) and legacy materials
+- Default gray color (0.8, 0.8, 0.8) for objects without materials
+
+#### Lights
+- **Sun Light**: Directional lighting with proper normal-based diffuse shading
+- **Point Light**: Omnidirectional light source with distance-based directional shading
+- **Spot Light**: Directional spotlight with diffuse shading
+- Light color and energy are respected
+
+#### Camera
+- Perspective projection
+- Uses camera's field of view and aspect ratio
+- Renders from camera viewpoint
+
+### Render Settings Panel
+
+When Blender Internal is selected as the render engine, a special settings panel appears showing:
+- Information about the renderer
+- List of supported features
+
+## Technical Details
+
+### Rendering Process
+
+1. **Scene Evaluation**: The addon evaluates the dependency graph to get the current scene state
+2. **Camera Setup**: Extracts camera position and projection parameters
+3. **Light Collection**: Gathers all lights in the scene
+4. **Mesh Processing**: For each mesh object:
+   - Transforms vertices to camera space
+   - Projects to screen space using perspective projection
+   - Calculates lighting per face
+   - Rasterizes polygons using scanline algorithm
+5. **Output**: Generates final image with proper colors
+
+### Lighting Model
+
+The renderer uses a simple Lambertian diffuse lighting model:
+- **Ambient**: Base illumination (0.1, 0.1, 0.1)
+- **Diffuse**: `color * light_color * light_energy * max(0, normal · light_direction)`
+
+### Rasterization
+
+Uses a point-in-polygon test with ray casting algorithm to determine which pixels belong to each face.
+
+## Limitations
+
+This is a basic reimplementation and has several limitations compared to the original Blender Internal renderer:
+
+- **No Raytracing**: Only scanline rendering
+- **No Shadows**: Shadow casting not implemented
+- **No Reflections/Refractions**: No recursive ray tracing
+- **Limited Material Properties**: Only base color is used
+- **No Texture Mapping**: Textures are not supported
+- **No Bump/Normal Maps**: Surface detail not supported
+- **Basic Lighting**: No advanced lighting features like area lights
+- **No Anti-aliasing**: Edges may appear jagged
+- **No Motion Blur**: Not implemented
+- **No Depth of Field**: Camera effects not supported
+- **No Viewport Preview**: Currently only works for final renders
+
+## Troubleshooting
+
+### Nothing Renders
+- Ensure you have a camera in the scene
+- Check that objects have geometry (vertices and faces)
+- Verify objects are in front of the camera
+
+### Black Render
+- Add lights to your scene (Sun or Point lights)
+- Check that light energy is > 0
+- Ensure objects have materials with non-black colors
+
+### Performance Issues
+- Reduce render resolution
+- Simplify mesh geometry
+- Reduce number of lights
+
+## Future Improvements
+
+Potential enhancements for future versions:
+- Viewport preview rendering
+- Shadow support
+- Texture mapping
+- Better anti-aliasing
+- Area lights
+- Specular highlights
+- Transparency and alpha blending
+- Ambient Occlusion
+- Global Illumination (basic)
+
+## Compatibility
+
+- **Blender Version**: 3.0+
+- **Dependencies**: numpy (usually included with Blender)
+- **Platform**: All platforms supported by Blender
+
+## License
+
+This is a community reimplementation project. The original Blender Internal renderer was developed by the Blender Foundation.
+
+## Credits
+
+- Original Blender Internal renderer: Blender Foundation
+- Reimplementation: Community contribution
+
+## Support
+
+For issues, feature requests, or contributions, please visit the project repository.