scripts/blender_optimize.py

"""
Blender optimization script for game-ready assets.
Run with: blender --background --python blender_optimize.py -- input.glb output.glb
"""

import bpy
import sys
from pathlib import Path
from mathutils import Vector


def optimize_asset(input_path: str, output_path: str):
    """Optimize GLB for game engine use."""
    
    print(f"[Blender] Optimizing: {input_path}")
    
    # Clear scene
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete()
    
    # Import GLB
    bpy.ops.import_scene.gltf(filepath=input_path)
    
    # Get imported object
    obj = bpy.context.selected_objects[0]
    bpy.context.view_layer.objects.active = obj
    
    # 1. Normalize scale to 2m height
    bbox = [obj.matrix_world @ Vector(corner) for corner in obj.bound_box]
    height = max(v.z for v in bbox) - min(v.z for v in bbox)
    if height > 0:
        scale_factor = 2.0 / height
        obj.scale = (scale_factor, scale_factor, scale_factor)
        bpy.ops.object.transform_apply(scale=True)
    
    # 2. Clean mesh topology
    bpy.ops.object.mode_set(mode='EDIT')
    bpy.ops.mesh.select_all(action='SELECT')
    bpy.ops.mesh.remove_doubles(threshold=0.0001)
    bpy.ops.mesh.normals_make_consistent(inside=False)
    bpy.ops.mesh.delete_loose()
    bpy.ops.mesh.dissolve_degenerate(threshold=0.0001)
    bpy.ops.object.mode_set(mode='OBJECT')
    
    # 3. Quad remesh for better topology
    mod = obj.modifiers.new(name="Remesh", type='REMESH')
    mod.mode = 'SHARP'
    mod.octree_depth = 7  # ~7,500 polygons
    mod.sharpness = 1.0
    mod.use_smooth_shade = True
    bpy.ops.object.modifier_apply(modifier="Remesh")
    
    # 4. Smart UV unwrap
    bpy.ops.object.mode_set(mode='EDIT')
    bpy.ops.mesh.select_all(action='SELECT')
    bpy.ops.uv.smart_project(
        angle_limit=66.0,
        island_margin=0.02,
        area_weight=1.0,
        correct_aspect=True,
        scale_to_bounds=True
    )
    bpy.ops.object.mode_set(mode='OBJECT')
    
    # 5. Apply smooth shading
    bpy.ops.object.shade_smooth()
    obj.data.use_auto_smooth = True
    obj.data.auto_smooth_angle = 0.523599  # 30 degrees
    
    # 6. Generate LOD levels
    lod_levels = [
        ("LOD0", 1.0),    # 100% - original
        ("LOD1", 0.5),    # 50% - medium distance
        ("LOD2", 0.25),   # 25% - far distance
    ]
    
    for lod_name, ratio in lod_levels:
        lod_obj = obj.copy()
        lod_obj.data = obj.data.copy()
        lod_obj.name = f"{obj.name}_{lod_name}"
        bpy.context.collection.objects.link(lod_obj)
        
        if ratio < 1.0:
            # Apply decimate modifier
            bpy.context.view_layer.objects.active = lod_obj
            mod = lod_obj.modifiers.new(name="Decimate", type='DECIMATE')
            mod.ratio = ratio
            bpy.ops.object.modifier_apply(modifier="Decimate")
    
    # 7. Generate collision mesh
    collision_obj = obj.copy()
    collision_obj.data = obj.data.copy()
    collision_obj.name = f"{obj.name}_collision"
    bpy.context.collection.objects.link(collision_obj)
    
    bpy.context.view_layer.objects.active = collision_obj
    
    # Simplify heavily for collision
    mod = collision_obj.modifiers.new(name="Decimate", type='DECIMATE')
    mod.ratio = 0.1  # 10% of original
    bpy.ops.object.modifier_apply(modifier="Decimate")
    
    # Convex hull for physics
    bpy.ops.object.mode_set(mode='EDIT')
    bpy.ops.mesh.select_all(action='SELECT')
    bpy.ops.mesh.convex_hull()
    bpy.ops.object.mode_set(mode='OBJECT')
    
    # 8. Export with Draco compression
    bpy.ops.export_scene.gltf(
        filepath=output_path,
        export_format='GLB',
        export_draco_mesh_compression_enable=True,
        export_draco_mesh_compression_level=6,
        export_draco_position_quantization=14,
        export_draco_normal_quantization=10,
        export_draco_texcoord_quantization=12,
        export_materials='EXPORT',
        export_colors=True,
        export_cameras=False,
        export_lights=False,
        export_apply=True,
        export_yup=True
    )
    
    print(f"[Blender] Optimization complete: {output_path}")


if __name__ == "__main__":
    # Parse command line arguments
    argv = sys.argv
    argv = argv[argv.index("--") + 1:]  # Get args after --
    
    if len(argv) < 2:
        print("Usage: blender --background --python blender_optimize.py -- input.glb output.glb")
        sys.exit(1)
    
    input_path = argv[0]
    output_path = argv[1]
    
    optimize_asset(input_path, output_path)