Reimplements the deprecated Blender Internal renderer (removed in 2.8) as a custom RenderEngine addon with scanline rasterization.

Core Implementation

RenderEngine (BlenderInternalRenderEngine)

• Scanline rasterizer with perspective projection and point-in-polygon testing
• Material extraction from Principled BSDF nodes and legacy diffuse colors
• Lambertian diffuse lighting: final_color = base_color × light_color × max(0, normal · light_dir)
• Three light types with proper directional calculations:
  • Sun: parallel rays from rotation matrix
  • Point: direction computed from light position to surface center
  • Spot: directional cone from rotation matrix

Rendering Pipeline

1. Evaluate depsgraph → extract camera matrix and lights
2. Transform mesh vertices to camera space
3. Project to screen space with depth culling (z > 0.1)
4. Calculate per-polygon lighting in world space
5. Rasterize using bounding box scan with ray casting

Example Usage

# In Blender UI:
# Render Properties → Render Engine → "Blender Internal"
# F12 to render with classic BI workflow

# Programmatic:
bpy.context.scene.render.engine = 'BLENDER_INTERNAL'
bpy.ops.render.render()

Files

• blender_internal_render.py - Main addon (340 lines)
• BLENDER_INTERNAL_README.md - Technical documentation
• QUICK_START.md - User guide with scene examples
• .gitignore - Python cache exclusions

Limitations

Intentionally minimal implementation:

• No textures, shadows, or reflections (scanline only, no raytracing)
• No viewport preview (final render only)
• No distance attenuation for point lights
• No anti-aliasing or complex material properties

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