Blender: Export the active curve object (U-component only)

io_export_curve.py

# This exporter just serializes Blender's bpy curve data API verbatim,
# so the exported json structure mirrors the variable names and
# arrays. The exporter only goes so far to export the U-component of
# the curve data, since we're more interested in curves and not NURBS
# surfaces for use in videogames. An asset importer in Unity need only
# look up the Blender Python API to choose how to interpret this data.

import bpy
import json
from bpy_extras.io_utils import ExportHelper

VERSION = 1

bl_info = {
    'name': 'Export Curve (.curve)',
    'author': 'Tamas Kemenczy',
    'blender': (2, 80, 0),
    'version': (0, 1),
    'description': 'Export the active curve object (U-component only)',
    'category': 'Import-Export',
}

def curve_to_dict(curve):
    splines = []
    curve_data = {
        'version': VERSION,
        'name': curve.name,
        'splines': splines,
    }
    for spline in curve.splines:
        points = []
        bezier_points = []
        spline_data = {
            'type': spline.type,
            'points': points,
            'bezier_points': bezier_points,
            'tilt_interpolation': spline.tilt_interpolation,
            'radius_interpolation': spline.radius_interpolation,
            'use_cyclic_u': spline.use_cyclic_u,
            'use_endpoint_u': spline.use_endpoint_u,
            'use_bezier_u': spline.use_bezier_u,
        }
        for p in spline.points:
            p_data = {
                'weight': p.weight,
                'tilt': p.tilt,
                'radius': p.radius,
                'point': list(p.co),
            }
            points.append(p_data)
        for bp in spline.bezier_points:
            bp_data = {
                'handle_left_type': bp.handle_left_type,
                'handle_right_type': bp.handle_right_type,
                'handle_left': list(bp.handle_left),
                'handle_right': list(bp.handle_right),
                'co': list(bp.co),
                'tilt': bp.tilt,
                'radius': bp.radius,
            }
            bezier_points.append(bp_data)
        splines.append(spline_data)
    return curve_data

class EXPORT_OTHER_OT_curve(bpy.types.Operator, ExportHelper):
    bl_idname = 'export_other.curve'
    bl_label = 'Export Curve (.curve)'
    bl_options = {'REGISTER'}

    filename_ext = ".curve"
    filter_glob: bpy.props.StringProperty(default="*.curve", options={'HIDDEN'})

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == 'CURVE'

    def execute(self, context):
        if not self.filepath:
            raise Exception("filepath not set")

        data = curve_to_dict(context.active_object.data)

        with open(self.filepath, 'w') as fp:
            json.dump(data, fp, indent=2, sort_keys=True)

        self.report({'INFO'}, 'Exported %s' % self.filepath)

        return {'FINISHED'}

classes = (
    EXPORT_OTHER_OT_curve,
)

def menu_func_export(self, context):
    self.layout.operator(EXPORT_OTHER_OT_curve.bl_idname, text="Curve (.curve)")

def register():
    for cls in classes:
        bpy.utils.register_class(cls)
    bpy.types.TOPBAR_MT_file_export.append(menu_func_export)

def unregister():
    bpy.types.TOPBAR_MT_file_export.remove(menu_func_export)
    for cls in classes:
        bpy.utils.unregister_class(cls)