3Dシーンの作成

Set up a complete Blender scene programmatically using the Python API (bpy). Configure scene hierarchy, add mesh objects, create PBR materials with node-based shaders, position lighting and cameras, and set up environment/world settings.

使用タイミング

• Creating reproducible 3D visualization scenes from scratch
• Automating product visualization or architectural rendering setup
• Generating multiple scene variations programmatically
• Building template scenes for batch rendering workflows
• Prototyping scene layouts before manual refinement
• Integrating 3D visualization into data pipelines or reporting systems

入力

/path/to/hdri.exr

product_model.obj

location=(7,-7,5)

lens=50mm

手順

1. Set Up Script Structure

Create a Python script with proper imports and structure:

#!/usr/bin/env python3
"""
Scene setup script for Blender.
Usage: blender --background --python setup_scene.py
"""

import bpy
import math
import os
from pathlib import Path

def clear_scene():
    """Remove all objects from the scene."""
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete(use_global=False)

    # Clear orphaned data
    for block in bpy.data.meshes:
        if block.users == 0:
            bpy.data.meshes.remove(block)

    for block in bpy.data.materials:
        if block.users == 0:
            bpy.data.materials.remove(block)

def main():
    clear_scene()
    # Scene setup steps follow

if __name__ == "__main__":
    main()

期待結果: Script structure with clear_scene() and main() functions 失敗時: Review Python syntax, check bpy import works in Blender Python environment

2. Add Mesh Objects

Create primitive or imported mesh objects:

def add_objects():
    """Add mesh objects to scene."""
    # Add cube
    bpy.ops.mesh.primitive_cube_add(
        size=2.0,
        location=(0, 0, 1)
    )
    cube = bpy.context.active_object
    cube.name = "Product_Base"

    # Add sphere
    bpy.ops.mesh.primitive_uv_sphere_add(
        radius=1.0,
        segments=32,
        ring_count=16,
        location=(3, 0, 1)
    )
    sphere = bpy.context.active_object
    sphere.name = "Detail_Sphere"

    # Import external model (optional)
    # bpy.ops.import_scene.obj(filepath="model.obj")

    return cube, sphere

期待結果: Objects appear in scene with correct names and positions 失敗時: Check operator syntax, verify coordinates, ensure no naming conflicts

3. Create Materials with Node-Based Shaders

Set up PBR materials using shader nodes:

def create_material(name, base_color, metallic=0.0, roughness=0.5):
    """Create a PBR material with node setup."""
    # Create material
    mat = bpy.data.materials.new(name=name)
    mat.use_nodes = True
    nodes = mat.node_tree.nodes
    links = mat.node_tree.links

    # Clear default nodes
    nodes.clear()

    # Add Principled BSDF
    node_bsdf = nodes.new(type='ShaderNodeBsdfPrincipled')
    node_bsdf.location = (0, 0)
    node_bsdf.inputs['Base Color'].default_value = base_color + (1.0,)  # Add alpha
    node_bsdf.inputs['Metallic'].default_value = metallic
    node_bsdf.inputs['Roughness'].default_value = roughness

    # Add Material Output
    node_output = nodes.new(type='ShaderNodeOutputMaterial')
    node_output.location = (300, 0)

    # Link nodes
    links.new(node_bsdf.outputs['BSDF'], node_output.inputs['Surface'])

    return mat

def apply_materials(cube, sphere):
    """Apply materials to objects."""
    # Create materials
    mat_red = create_material("RedPlastic", (0.8, 0.1, 0.1), metallic=0.0, roughness=0.4)
    mat_metal = create_material("Metal", (0.8, 0.8, 0.8), metallic=1.0, roughness=0.2)

    # Assign to objects
    if cube.data.materials:
        cube.data.materials[0] = mat_red
    else:
        cube.data.materials.append(mat_red)

    if sphere.data.materials:
        sphere.data.materials[0] = mat_metal
    else:
        sphere.data.materials.append(mat_metal)

期待結果: Materials visible in shader editor with proper node connections 失敗時: Check node types exist, verify link syntax, ensure color values in [0,1] range

4. Set Up Lighting

Configure lights for scene illumination:

def setup_lighting():
    """Add lights to scene."""
    # Sun light
    bpy.ops.object.light_add(
        type='SUN',
        location=(5, 5, 10)
    )
    sun = bpy.context.active_object
    sun.name = "KeyLight"
    sun.data.energy = 3.0
    sun.rotation_euler = (math.radians(45), 0, math.radians(45))

    # Area light (fill light)
    bpy.ops.object.light_add(
        type='AREA',
        location=(-4, -4, 6)
    )
    area = bpy.context.active_object
    area.name = "FillLight"
    area.data.energy = 200.0
    area.data.size = 5.0
    area.rotation_euler = (math.radians(60), 0, math.radians(-135))

    # Point light (rim light)
    bpy.ops.object.light_add(
        type='POINT',
        location=(2, -5, 3)
    )
    point = bpy.context.active_object
    point.name = "RimLight"
    point.data.energy = 500.0

期待結果: Three lights with appropriate intensities and positions 失敗時: Adjust energy values for render engine (Cycles vs EEVEE), check rotation format

5. Position Camera

Set up camera with proper framing:

def setup_camera():
    """Add and configure camera."""
    bpy.ops.object.camera_add(
        location=(7, -7, 5)
    )
    camera = bpy.context.active_object
    camera.name = "MainCamera"

    # Point camera at origin
    direction = (0, 0, 1) - camera.location
    rot_quat = direction.to_track_quat('-Z', 'Y')
    camera.rotation_euler = rot_quat.to_euler()

    # Camera settings
    camera.data.lens = 50  # Focal length in mm
    camera.data.dof.use_dof = True
    camera.data.dof.focus_distance = 10.0
    camera.data.dof.aperture_fstop = 2.8

    # Set as active camera
    bpy.context.scene.camera = camera

期待結果: Camera positioned with correct focal length and DOF settings 失敗時: Use simpler rotation method if track_to fails, verify lens units

6. Configure World Environment

Set up world shader and background:

def setup_world():
    """Configure world environment."""
    world = bpy.data.worlds['World']
    world.use_nodes = True
    nodes = world.node_tree.nodes
    links = world.node_tree.links

    # Clear default nodes
    nodes.clear()

    # Add Environment Texture (for HDRI)
    node_env = nodes.new(type='ShaderNodeTexEnvironment')
    node_env.location = (-300, 0)

    # Load HDRI if available
    hdri_path = "/path/to/hdri.exr"
    if os.path.exists(hdri_path):
        node_env.image = bpy.data.images.load(hdri_path)

    # Add Background shader
    node_bg = nodes.new(type='ShaderNodeBackground')
    node_bg.location = (0, 0)
    node_bg.inputs['Strength'].default_value = 1.0

    # Add World Output
    node_output = nodes.new(type='ShaderNodeOutputWorld')
    node_output.location = (300, 0)

    # Link nodes
    links.new(node_env.outputs['Color'], node_bg.inputs['Color'])
    links.new(node_bg.outputs['Background'], node_output.inputs['Surface'])

期待結果: World shader with HDRI or solid background configured 失敗時: Skip HDRI loading if file missing, use Background node alone with color

7. Configure Render Settings

Set basic render parameters:

def setup_render_settings():
    """Configure render settings."""
    scene = bpy.context.scene

    # Render engine
    scene.render.engine = 'CYCLES'  # or 'BLENDER_EEVEE'
    scene.cycles.samples = 128
    scene.cycles.use_denoising = True

    # Output settings
    scene.render.resolution_x = 1920
    scene.render.resolution_y = 1080
    scene.render.resolution_percentage = 100

    # File format
    scene.render.image_settings.file_format = 'PNG'
    scene.render.image_settings.color_mode = 'RGBA'
    scene.render.image_settings.color_depth = '16'
    scene.render.filepath = "/tmp/render_"

期待結果: Render settings configured, ready for rendering 失敗時: Check engine name spelling, verify resolution values are positive integers

8. Organize Scene Hierarchy

Create collections for organization:

def organize_collections():
    """Organize objects into collections."""
    # Create collections
    col_geometry = bpy.data.collections.new("Geometry")
    col_lights = bpy.data.collections.new("Lights")
    col_cameras = bpy.data.collections.new("Cameras")

    # Link to scene
    bpy.context.scene.collection.children.link(col_geometry)
    bpy.context.scene.collection.children.link(col_lights)
    bpy.context.scene.collection.children.link(col_cameras)

    # Move objects to collections
    for obj in bpy.data.objects:
        # Unlink from main collection
        bpy.context.scene.collection.objects.unlink(obj)

        # Link to appropriate collection
        if obj.type == 'MESH':
            col_geometry.objects.link(obj)
        elif obj.type == 'LIGHT':
            col_lights.objects.link(obj)
        elif obj.type == 'CAMERA':
            col_cameras.objects.link(obj)

期待結果: Objects organized in named collections for easier management 失敗時: Check collection already exists before creating, handle orphaned objects

バリデーション Checklist

• Script runs without errors in Blender background mode
• All expected objects present in scene outliner
• Materials show correct colors and properties in shader editor
• Camera positioned with objects in frame
• Lighting provides adequate illumination (test render)
• World environment loads correctly (HDRI or background color)
• Render settings configured appropriately for output requirements
• Scene organized logically in collections
• No orphaned data blocks (materials, meshes without users)
• Script includes clear_scene() for reproducibility

よくある落とし穴

1. Object naming conflicts: Use unique names, check for existing objects before creating
2. Incorrect color format: RGB values must be tuples (r, g, b, a) in [0,1] range
3. Missing alpha channel: When setting colors, include alpha:

   (r, g, b, 1.0)

4. Node connection errors: Verify node types have expected inputs/outputs before linking
5. Camera not active: Must set

   bpy.context.scene.camera = camera_object

6. Relative vs absolute paths: Use absolute paths or Path() for cross-platform compatibility
7. Units confusion: Blender uses meters by default, camera lens in millimeters
8. Rotation formats: Use

   math.radians()

   for degree-to-radian conversion
9. Render engine differences: EEVEE and Cycles have different features and parameters
10. Memory leaks: Clear orphaned data blocks to prevent memory buildup in batch operations

関連スキル

• script-blender-automation: Advanced scripting patterns for procedural modeling and batch operations
• render-blender-output: Configure rendering pipeline and execute renders
• create-2d-composition: 2D graphics composition using similar scripting approaches