OnMouseDrag is called when the user has clicked on a GUIElement or Collider and is still holding down the mouse.

OnMouseDrag is called every frame while the mouse is down.

	// Darken the material color while user holds down the mouse.
	function OnMouseDrag () {
		renderer.material.color -= Color.white * Time.deltaTime;
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnMouseDrag() {
        renderer.material.color -= Color.white * Time.deltaTime;
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnMouseDrag() as void:
		renderer.material.color -= (Color.white * Time.deltaTime)

This function is not called on objects that belong to Ignore Raycast layer.

OnMouseDrag can be a co-routine, simply use the yield statement in the function. This event is sent to all scripts attached to the Collider or GUIElement.