Material instance overview — MRTK3

The MaterialInstance behavior aides in tracking instance material lifetime and automatically destroys instanced materials for the user. This utility component can be used as a replacement to Renderer.material or Renderer.materials.

Why can using Renderer.material be an issue? If you add the below code to a Unity scene and hit play memory usage will continue to climb and climb:

public class Leak : MonoBehaviour
{
    private void Update()
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        // Memory leak, the material allocated is not tracked & destroyed.
        cube.GetComponent<Renderer>().material.color = Color.red;
        ...
        Destroy(cube);
    }
}

As an alternative try using the MaterialInstance behavior:

public class NoLeak : MonoBehaviour
{
    private void Update()
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        // No memory leak, the material allocated is tracked & destroyed by MaterialInstance.
        cube.EnsureComponent<MaterialInstance>().Material.color = Color.red;
        ...
        Destroy(cube);
    }
}

Usage

When invoking Unity's Renderer.material(s), Unity automatically instantiates new materials. It is the caller's responsibility to destroy the materials when a material is no longer needed or the game object is destroyed. The MaterialInstance behavior helps avoid material leaks and keeps material allocation paths consistent during edit and run time.

When a MaterialPropertyBlock can not be used and a material must be instanced, MaterialInstance can be used as follows:

public class MyBehaviour : MonoBehaviour
{
    // Assigned via the inspector.
    public Renderer targetRenderer;

    private void OnEnable()
    {
        Material material = targetRenderer.EnsureComponent<MaterialInstance>().Material;
        material.color = Color.red;
        ...
    }
}

If multiple objects need ownership of the material instance it's best to take explicit ownership for reference tracking. (An optional interface called IMaterialInstanceOwner exists to aide with ownership.) Below is example usage:

public class MyBehaviour : MonoBehaviour,  IMaterialInstanceOwner
{
    // Assigned via the inspector.
    public Renderer targetRenderer;

    private void OnEnable()
    {
        Material material = targetRenderer.EnsureComponent<MaterialInstance>().AcquireMaterial(this);
        material.color = Color.red;
        ...
    }

    private void OnDisable()
    {
        targetRenderer.GetComponent<MaterialInstance>()?.ReleaseMaterial(this)
    }

    public void OnMaterialChanged(MaterialInstance materialInstance)
    {
        // Optional method for when materials change outside of the MaterialInstance.
        ...
    }
}

For more information please see the example usage demonstrated within the ClippingPrimitive behavior.

See also

• Clipping Primitive
• Standard Shader