blender-add-on-development

Develop, debug, and upgrade Blender add-ons/plugins and `bpy` scripts with Blender 4.x and 5.x compatibility. Use when tasks involve generating new add-on code, scaffolding operators/panels, migrating deprecated Python API calls, resolving Blender version breakages, or validating scripts against Blender 4/5 API changes.

Blender Plugin Development

Quick Start

1. Confirm target Blender versions (minimum and maximum expected).
2. Read references/blender4_to_5_compat.md before writing or patching code.
3. Scaffold a new add-on package with scripts/scaffold_addon.py when requested.
4. Implement requested behavior with explicit compatibility guards for 4.x and 5.x.
5. Validate syntax and registration flow before returning code.

Workflow

1) Scope the task

• Extract target behavior, UI location, operator names, and data model.
• Ask for Blender version range if unspecified; default to >= 4.0 with 5.x awareness.
• Decide whether output should be:
  • A full add-on package.
  • A standalone bpy script.
  • A migration patch to existing code.

2) Generate a baseline when creating a new add-on

• Run:
  • python3 scripts/scaffold_addon.py --name "<Addon Name>" --output <target-dir>
• Customize generated __init__.py, operators.py, ui.py, and compat.py for the feature request.
• Keep bl_info["blender"] at the minimum supported version (for this skill, usually (4, 0, 0) or higher).

3) Implement compatibility-safe code

• Use bpy.app.version gates only when behavior truly diverges.
• Prefer compatibility wrappers in compat.py over scattered version checks.
• Avoid APIs called out as removed/deprecated in references/blender4_to_5_compat.md.
• For operator context overrides, use context.temp_override(...).
• For assets, prefer context.asset and AssetRepresentation.
• For GPU drawing in 5.x, avoid bgl and migrate to gpu.

4) Validate before returning code

• Run python3 -m py_compile on changed Python files.
• If Blender binaries are available, run headless smoke tests:
  • blender --background --factory-startup --python <smoke_test.py>
• Check register/unregister order and operator bl_idname format.
• Confirm no removed API names remain in generated output.

Script Generation Patterns

• Generate small, composable files:
  • operators.py for operators.
  • ui.py for panels/menus.
  • compat.py for version shims.
  • __init__.py for bl_info and registration entrypoints.
• Use idempotent register/unregister functions.
• Keep class lists explicit (tuple of classes) and unregister in reverse order.
• Report actionable failures with self.report({"ERROR"}, "...") inside operators.
• Avoid hard-coded context assumptions in poll() and execute().

Required Compatibility Rules

• Avoid dict-like access for runtime-defined RNA properties in 5.0 when accessing add-on-defined data; use supported property access patterns documented in Blender 5.0 release notes.
• Never depend on bundled private modules listed in Blender 5.0 notes (for example, bl_ui_utils, rna_info).
• Treat scene.use_nodes as deprecated and avoid using it for new code.
• Avoid UILayout.template_asset_view() in new code; use asset-shelf-compatible APIs.
• Keep code ready for Blender 6.0 removals by addressing documented 5.0 deprecations proactively.

Resources (optional)

scripts/

• scripts/scaffold_addon.py: Generate a Blender 4/5-ready add-on package skeleton.

references/

• references/blender4_to_5_compat.md: Blender 4.0 and 5.0 compatibility map with official sources.
• references/script_generation_patterns.md: Reusable patterns for operators, panels, and background scripts.