Recreating 3ds Max Rig Constraints in Blender with Python and JSON

import bpy
import json
import os

# --- Configuration ---
JSON_FILE_PATH = r"Z:\_vm_host\heart\constraints_only.json"
ARMATURE_NAME = "heart_rig"

# Mapping 3ds Max constraint classes to Blender constraint types
CONSTRAINT_MAPPING = {
    "Position_Constraint": "COPY_LOCATION",
    "Orientation_Constraint": "COPY_ROTATION",
    "Rotation_Constraint": "COPY_ROTATION",
    "LookAt_Constraint": "TRACK_TO",
}

def apply_bone_constraints():
    if not os.path.exists(JSON_FILE_PATH):
        print(f"Error: Could not find JSON file at '{JSON_FILE_PATH}'")
        return

    armature_obj = bpy.data.objects.get(ARMATURE_NAME)
    if not armature_obj or armature_obj.type != 'ARMATURE':
        print(f"Error: Armature '{ARMATURE_NAME}' not found or is not an armature.")
        return

    with open(JSON_FILE_PATH, 'r', encoding='utf-8') as f:
        constraints_data = json.load(f)

    print("-" * 40)
    print(f"Starting Constraint Import for Armature: {ARMATURE_NAME}...")

    # Ensure we're in object mode before manipulating pose bones
    if bpy.context.object and bpy.context.object.mode != 'OBJECT':
        bpy.ops.object.mode_set(mode='OBJECT')

    # Track any unsupported or skipped constraints for the final summary
    skipped_constraint_types = set()

    for item in constraints_data:
        bone_name = item.get("obj")
        pbone = armature_obj.pose.bones.get(bone_name)
        
        if not pbone:
            # Uncomment if you want verbose logs on missing bones
            # print(f"Warning: Bone '{bone_name}' not found. Skipping.")
            continue
            
        for c_data in item.get("constraints", []):
            max_type = c_data.get("type", "").strip()
            
            # Explicitly skip Path constraints
            if "Path_Constraint" in max_type or "Path" in max_type:
                skipped_constraint_types.add(max_type)
                continue
                
            blender_type = CONSTRAINT_MAPPING.get(max_type)
            if not blender_type:
                skipped_constraint_types.add(max_type)
                continue
                
            targets = c_data.get("target_weight", [])
            if not targets:
                continue

            current_weight_sum = 0.0
            
            for target_name, weight in targets:
                target_pbone = armature_obj.pose.bones.get(target_name)
                if not target_pbone:
                    print(f"Warning: Target bone '{target_name}' not found for '{bone_name}'.")
                    continue
                
                b_constraint = pbone.constraints.new(type=blender_type)
                b_constraint.name = max_type
                b_constraint.target = armature_obj
                b_constraint.subtarget = target_name
                
                # Normalize weights sequentially across multiple targets
                current_weight_sum += weight
                if current_weight_sum > 0:
                    b_constraint.influence = weight / current_weight_sum
                else:
                    b_constraint.influence = 0.0
                    
                # Default bone tracking axes for Blender
                if blender_type == "TRACK_TO":
                    b_constraint.track_axis = 'TRACK_Y'
                    b_constraint.up_axis = 'UP_Z'

    print("Constraint Import Complete.")
    
    # --- Summary of Skipped Constraints ---
    if skipped_constraint_types:
        print("-" * 40)
        print("SUMMARY OF SKIPPED / UNMAPPED CONSTRAINTS:")
        for skipped_type in sorted(skipped_constraint_types):
            print(f" - {skipped_type}")
            
    print("-" * 40)

if __name__ == "__main__":
    apply_bone_constraints()