script-blender-automation

# Script Blender Automation

Advanced Blender Python scripting for procedural modeling, keyframe animation, batch operations, operator registration, and add-on development. Covers complex geometry generation, automated workflows, and integration with external data sources.

## When to Use

- Automating repetitive modeling or animation tasks
- Generating procedural geometry from algorithms or data
- Creating batch rendering pipelines with parameter variations
- Building custom operators or add-ons for workflow enhancement
- Integrating Blender with external data pipelines or APIs
- Scripting complex animations with mathematical precision
- Developing reusable tools for team workflows

## Inputs

| Input | Type | Description | Example |
|-------|------|-------------|---------|
| Automation requirements | Specification | Task description, parameters, constraints | Render 100 variations, animate path from data |
| Data sources | Files/APIs | External data for procedural generation | CSV coordinates, JSON parameters, API responses |
| Algorithm definitions | Code/Math | Procedural generation logic | Fractal patterns, parametric curves, L-systems |
| Operator specifications | Requirements | Custom tool behavior and UI | Tool name, properties, modal interaction |
| Animation parameters | Keyframes/Data | Timing, easing, constraints | Frame ranges, interpolation curves |

## Procedure

### 1. Procedural Geometry Generation

Create mesh geometry programmatically using BMesh:

```python
import bpy
import bmesh
import math

def create_parametric_surface(name, u_res=32, v_res=32):
    """Generate parametric surface using mathematical function."""
    mesh = bpy.data.meshes.new(name)
    obj = bpy.data.objects.new(name, mesh)
    bpy.context.collection.objects.link(obj)

    bm = bmesh.new()

    # Create vertices using parametric equations
    verts = []
    for i in range(u_res):
        for j in range(v_res):
            u = (i / (u_res - 1)) * 2 * math.pi
            v = (j / (v_res - 1)) * math.pi

            # Sphere parametric equations
            x = math.sin(v) * math.cos(u)
            y = math.sin(v) * math.sin(u)
            z = math.cos(v)

            vert = bm.verts.new((x, y, z))
            verts.append(vert)

    # Create faces
    bm.verts.ensure_lookup_table()
    for i in range(u_res - 1):
        for j in range(v_res - 1):
            v1 = verts[i * v_res + j]
            v2 = verts[(i + 1) * v_res + j]
            v3 = verts[(i + 1) * v_res + (j + 1)]
            v4 = verts[i * v_res + (j + 1)]
            bm.faces.new([v1, v2, v3, v4])

    # Write to mesh
    bm.to_mesh(mesh)
    bm.free()

    return obj
```

**Got:** Complex geometry generated from mathematical functions
**If fail:** Check BMesh API calls, verify vertex indexing, ensure faces are manifold

### 2. Keyframe Animation Automation

Script animation keyframes and drivers:

```python
def animate_rotation(obj, start_frame=1, end_frame=250, axis='Z', rotations=2):
    """Animate object rotation over time."""
    # Set initial keyframe
    obj.rotation_euler[2] = 0  # Z axis
    obj.keyframe_insert(data_path="rotation_euler", index=2, frame=start_frame)

    # Set end keyframe
    obj.rotation_euler[2] = rotations * 2 * math.pi
    obj.keyframe_insert(data_path="rotation_euler", index=2, frame=end_frame)

    # Set interpolation
    if obj.animation_data and obj.animation_data.action:
        for fcurve in obj.animation_data.action.fcurves:
            if 'rotation_euler' in fcurve.data_path:
                for keyframe in fcurve.keyframe_points:
                    keyframe.interpolation = 'LINEAR'

def animate_material_property(mat, property_path, values, frames):
    """Animate material node values."""
    if not mat.node_tree:
        return

    # Example: animate emission strength
    nodes = mat.node_tree.nodes
    emission = nodes.get('Emission')
    if emission:
        for frame, value in zip(frames, values):
            emission.inputs['Strength'].default_value = value
            emission.inputs['Strength'].keyframe_insert(
                data_path="default_value",
                frame=frame
            )

def create_driver(obj, property_path, expression):
    """Create driver for automated animation."""
    driver = obj.driver_add(property_path)
    driver.driver.type = 'SCRIPTED'
    driver.driver.expression = expression

    # Example: link rotation to frame number
    # expression = "frame / 10"
```

**Got:** Keyframes inserted, animation plays back correctly
**If fail:** Check property paths, verify data_path syntax, ensure objects are keyable

### 3. Batch Processing Operations

Process multiple objects or files in batch:

```python
import os
from pathlib import Path

def batch_import_and_render(input_dir, output_dir, file_pattern="*.obj"):
    """Import multiple files and render each."""
    input_path = Path(input_dir)
    output_path = Path(output_dir)
    output_path.mkdir(exist_ok=True)

    scene = bpy.context.scene

    for obj_file in input_path.glob(file_pattern):
        # Clear existing objects
        bpy.ops.object.select_all(action='SELECT')
        bpy.ops.object.delete()

        # Import model
        bpy.ops.import_scene.obj(filepath=str(obj_file))

        # Setup camera and lighting (reuse setup functions)
        setup_camera()
        setup_lighting()

        # Render
        output_file = output_path / f"{obj_file.stem}.png"
        scene.render.filepath = str(output_file)
        bpy.ops.render.render(write_still=True)

        print(f"Rendered: {output_file}")

def batch_material_variation(base_object, colors, output_prefix):
    """Render object with multiple material colors."""
    mat = base_object.data.materials[0]
    bsdf = mat.node_tree.nodes.get('Principled BSDF')

    if not bsdf:
        return

    for i, color in enumerate(colors):
        # Update material color
        bsdf.inputs['Base Color'].default_value = color + (1.0,)

        # Render
        bpy.context.scene.render.filepath = f"{output_prefix}_{i:03d}.png"
        bpy.ops.render.render(write_still=True)
```

**Got:** Multiple files processed, renders generated for each variant
**If fail:** Check file paths exist, verify import operators, handle missing materials

### 4. Custom Operator Development

Create custom operators for reusable tools:

```python
import bpy
from bpy.props import FloatProperty, IntProperty

class OBJECT_OT_generate_spiral(bpy.types.Operator):
    """Generate a spiral curve"""
    bl_idname = "object.generate_spiral"
    bl_label = "Generate Spiral"
    bl_options = {'REGISTER', 'UNDO'}

    # Operator properties
    radius: FloatProperty(
        name="Radius",
        description="Spiral radius",
        default=2.0,
        min=0.1,
        max=10.0
    )

    turns: IntProperty(
        name="Turns",
        description="Number of spiral turns",
        default=5,
        min=1,
        max=20
    )

    resolution: IntProperty(
        name="Resolution",
        description="Points per turn",
        default=32,
        min=8,
        max=128
    )

    def execute(self, context):
        # Create curve
        curve = bpy.data.curves.new('Spiral', 'CURVE')
        curve.dimensions = '3D'

        spline = curve.splines.new('NURBS')
        num_points = self.turns * self.resolution

        spline.points.add(num_points - 1)  # -1 because one point exists

        for i in range(num_points):
            t = i / self.resolution
            angle = t * 2 * math.pi

            x = self.radius * math.cos(angle)
            y = self.radius * math.sin(angle)
            z = t * 0.5

            spline.points[i].co = (x, y, z, 1.0)

        # Create object
        obj = bpy.data.objects.new('Spiral', curve)
        context.collection.objects.link(obj)
        obj.select_set(True)
        context.view_layer.objects.active = obj

        self.report({'INFO'}, f"Generated spiral with {num_points} points")
        return {'FINISHED'}

def register():
    bpy.utils.register_class(OBJECT_OT_generate_spiral)

def unregister():
    bpy.utils.unregister_class(OBJECT_OT_generate_spiral)

if __name__ == "__main__":
    register()
```

**Got:** Operator appears in search, executes with proper undo support
**If fail:** Check bl_idname format (lowercase with underscores), verify property types

### 5. Modal Operator for Interactive Tools

Create interactive modal operators:

```python
class OBJECT_OT_modal_scale(bpy.types.Operator):
    """Interactive scaling with mouse"""
    bl_idname = "object.modal_scale"
    bl_label = "Modal Scale"
    bl_options = {'REGISTER', 'UNDO'}

    def __init__(self):
        self.initial_mouse_x = 0
        self.initial_scale = 1.0

    def modal(self, context, event):
        if event.type == 'MOUSEMOVE':
            # Calculate scale based on mouse movement
            delta = event.mouse_x - self.initial_mouse_x
            scale = self.initial_scale + (delta / 100.0)
            scale = max(0.1, scale)  # Minimum scale

            # Apply to active object
            context.active_object.scale = (scale, scale, scale)

        elif event.type == 'LEFTMOUSE':
            return {'FINISHED'}

        elif event.type in {'RIGHTMOUSE', 'ESC'}:
            # Cancel - restore initial scale
            context.active_object.scale = (
                self.initial_scale,
                self.initial_scale,
                self.initial_scale
            )
            return {'CANCELLED'}

        return {'RUNNING_MODAL'}

    def invoke(self, context, event):
        if context.active_object:
            self.initial_mouse_x = event.mouse_x
            self.initial_scale = context.active_object.scale[0]

            context.window_manager.modal_handler_add(self)
            return {'RUNNING_MODAL'}
        else:
            self.report({'WARNING'}, "No active object")
            return {'CANCELLED'}
```

**Got:** Interactive operator responds to mouse, left-click confirms, ESC cancels
**If fail:** Check event types, ensure modal handler is added, handle no active object

### 6. Add-on Packaging

Structure code as installable add-on:

```python
bl_info = {
    "name": "Custom Tools",
    "author": "Your Name",
    "version": (1, 0, 0),
    "blender": (3, 0, 0),
    "location": "View3D > Add > Mesh",
    "description": "Collection of custom modeling tools",
    "category": "Add Mesh",
}

import bpy

# Import operator classes
from .operators import OBJECT_OT_generate_spiral

classes = (
    OBJECT_OT_generate_spiral,
    # Add other classes
)

def menu_func(self, context):
    """Add to menu."""
    self.layout.operator(OBJECT_OT_generate_spiral.bl_idname)

def register():
    for cls in classes:
        bpy.utils.register_class(cls)

    bpy.types.VIEW3D_MT_mesh_add.append(menu_func)

def unregister():
    bpy.types.VIEW3D_MT_mesh_add.remove(menu_func)

    for cls in reversed(classes):
        bpy.utils.unregister_class(cls)

if __name__ == "__main__":
    register()
```

**Got:** Add-on installs via Preferences, operators appear in menus
**If fail:** Check bl_info format, verify Blender version requirement, ensure all classes listed

### 7. Data-Driven Procedural Generation

Generate geometry from external data:

```python
import csv
import json

def create_from_csv(filepath):
    """Generate objects from CSV data."""
    with open(filepath, 'r') as f:
        reader = csv.DictReader(f)

        for row in reader:
            # Parse data
            name = row['name']
            x, y, z = float(row['x']), float(row['y']), float(row['z'])
            scale = float(row.get('scale', 1.0))

            # Create object
            bpy.ops.mesh.primitive_uv_sphere_add(location=(x, y, z))
            obj = bpy.context.active_object
            obj.name = name
            obj.scale = (scale, scale, scale)

def create_from_json(filepath):
    """Generate scene from JSON configuration."""
    with open(filepath, 'r') as f:
        config = json.load(f)

    # Process objects
    for obj_config in config.get('objects', []):
        obj_type = obj_config['type']
        location = obj_config['location']

        if obj_type == 'cube':
            bpy.ops.mesh.primitive_cube_add(location=location)
        elif obj_type == 'sphere':
            bpy.ops.mesh.primitive_uv_sphere_add(location=location)

        obj = bpy.context.active_object
        obj.name = obj_config.get('name', 'Object')

        # Apply material if specified
        if 'material' in obj_config:
            mat_name = obj_config['material']
            mat = bpy.data.materials.get(mat_name)
            if mat:
                obj.data.materials.append(mat)
```

**Got:** Objects created based on external data files
**If fail:** Validate file format, handle missing fields, provide default values

## Validation Checklist

- [ ] Scripts run without errors in Blender Python environment
- [ ] Procedural geometry generates as expected
- [ ] Animation keyframes inserted at correct frames
- [ ] Batch operations process all files successfully
- [ ] Custom operators appear in search and execute correctly
- [ ] Modal operators respond to mouse/keyboard events
- [ ] Add-ons install and uninstall cleanly
- [ ] External data files parsed correctly
- [ ] Error handling covers edge cases
- [ ] Code follows PEP 8 style guidelines

## Pitfalls

1. **Circular imports in add-ons**: Use relative imports, structure modules carefully
2. **Operator naming**: bl_idname must be lowercase with single underscore (category.name)
3. **Property types**: Use correct bpy.props types (FloatProperty, IntProperty, etc.)
4. **Context access**: Not all operators work in all contexts (viewport vs render)
5. **BMesh cleanup**: Always call `bm.free()` after `bm.to_mesh()` to prevent memory leaks
6. **Animation keyframe timing**: Frame numbers start at 1, not 0
7. **Driver expression errors**: Validate expressions, use safe namespace
8. **Modal operator blocking**: Don't block in modal(), use non-blocking operations
9. **Add-on installation paths**: Place in Blender's scripts/addons directory
10. **Version compatibility**: API changes between Blender versions, document requirements

## Related Skills

- **[create-3d-scene](../create-3d-scene/SKILL.md)**: Basic scene setup and object creation
- **[render-blender-output](../render-blender-output/SKILL.md)**: Rendering workflows for automated output
- **[create-r-package](../../r-packages/create-r-package/SKILL.md)**: Similar packaging patterns for code distribution