Scripted Importers

Scripted Importers are part of the Unity Scripting API. You can use Scripted Importers to write custom Asset importers in C# for file formats not natively supported by Unity.

Create a custom importer by specializing the abstract class ScriptedImporter and applying the ScriptedImporter attribute. This registers your custom importer to handle one or more file extensions. When a file matching the registered file extensions is detected by the Asset pipeline as being new or changed, Unity invokes the method OnImportAsset of your custom importer.

Note: Scripted Importers cannot handle a file extension that is already natively handled by Unity.

Ejemplo

Below is a simple example as Scripted Importer: It imports asset files with the extension “cube” into a Unity Prefab with a cube primitive as the main Asset and a default material with a color fetched from the Asset file:

using UnityEngine;
using UnityEditor.AssetImporters;
using System.IO;

[ScriptedImporter(1, "cube")]
public class CubeImporter : ScriptedImporter
{
    public float m_Scale = 1;

    public override void OnImportAsset(AssetImportContext ctx)
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        var position = JsonUtility.FromJson<Vector3>(File.ReadAllText(ctx.assetPath));

        cube.transform.position = position;
        cube.transform.localScale = new Vector3(m_Scale, m_Scale, m_Scale);

        // 'cube' is a a GameObject and will be automatically converted into a prefab
        // (Only the 'Main Asset' is elligible to become a Prefab.)
        ctx.AddObjectToAsset("main obj", cube);
        ctx.SetMainObject(cube);

        var material = new Material(Shader.Find("Standard"));
        material.color = Color.red;

        // Assets must be assigned a unique identifier string consistent across imports
        ctx.AddObjectToAsset("my Material", material);

        // Assets that are not passed into the context as import outputs must be destroyed
        var tempMesh = new Mesh();
        DestroyImmediate(tempMesh);
    }
}

Note:

• The importer is registered with Unity’s Asset pipeline by placing the the ScriptedImporter attribute on the CubeImporter class.
• The CubeImporter class implements the abstract ScriptedImporter base class.
• OnImportAsset’s ctx argument contains both input and output data for the import event.
• Each import event must generate one (and only one) call to SetMainAsset.
• Each import event may generate as many calls to AddSubAsset as necessary.
• Please refer to the Scripting API documentation for more details.

You may also implement a custom Import Settings Editor by specializing ScriptedImporterEditor class and decorating it with the class attribute CustomEditor to tell it what type of importer it is used for.

Por ejemplo:

using UnityEditor;
using UnityEditor.AssetImporters;
using UnityEditor.SceneManagement;
using UnityEngine;

[CustomEditor(typeof(CubeImporter))]
public class CubeImporterEditor: ScriptedImporterEditor
{
    public override void OnInspectorGUI()
    {
        var colorShift = new GUIContent("Color Shift");
        var prop = serializedObject.FindProperty("m_ColorShift");
        EditorGUILayout.PropertyField(prop, colorShift);
        base.ApplyRevertGUI();
    }
}

Using a Scripted Importer

Once you have added a scripted importer class to a project, you may use it just like any other native file type supported by Unity:

• Drop a supported file in the Asset directory hierarchy to import.
• Restarting the Unity Editor reimports any files that have changed since last update.
• Editing the Asset file on disk and returning to the Unity Editor triggers a reimport.
• Import a new asset using Asset > Import New Asset….
• Explicitly trigger a re-import via the menu: Asset > Reimport.
• Click on the Asset to see its settings in the Inspector window. To modify its settings, edit them in the Inspector window and click Apply .
  
  

Real-world use of Scripted Importers

• Alembic: The Alembic importer plug-in has been updated to use a Scripted Importer. For more information, visit Unity github: AlembicImporter.

• USD: The USD importer plug-in has been updated to use a Scripted Importer. For more information, please visit Unity github:: USDForUnity.