change materials onmousedrag

Hi! Here's an example of something easy you could do. Attach the "original" material to the object (through the mesh renderer), and the "new" material to a public variable in a script. Then just switch between the two in the code. I did a quick test and it seemed to work. Here's a little example:

 using UnityEngine;
 using System.Collections;
 
 public class MatSwitchTest : MonoBehaviour {
     
     public Material newMat;
     Material oldMat;
     
     void Start() {
         oldMat = this.renderer.material;
     }
 
     void OnMouseDrag () {
         this.renderer.material = newMat;
     }
     
     void OnMouseUp () {
         this.renderer.material = oldMat;
     }
 }

This is if you want to swap the entire material like you asked. Maybe in your situation, though, you can just switch back and forth from a shader that doesn't do transparency to one that does. It's pretty similar.

Sorry.. ill try to be more accurate..

Im doing a tower defense game, and i have a interactive GUI which let me drag the "towers" from the GUI to the scene. The code that manages that is:

 using UnityEngine;
 using System.Collections;
 
 public class Gui : MonoBehaviour {
     
     public Transform clone;
     public Transform ObjectToPlace;
     private GameObject obj;
 
     private Vector3 screenPoint;
     private Vector3 offset;
     private Vector3 mousePos;
     private Ray ray2;
     private RaycastHit hit2;
     int layerMask2;
     
     public bool dest=false;
     
     private Rect boton1=new Rect(10, 40, 50, 80);
     private Rect boton2=new Rect(70, 40, 50, 80);
     
     
     void OnGUI() {
         
         GUI.BeginGroup(new Rect(0, Screen.height-100, Screen.width, 100));
         
         GUI.Box(new Rect(0, 0, Screen.width, 100),"");
         
         CheckButton(boton1,1);
         CheckButton(boton2,2);
         GUI.Button(boton1,"");
         GUI.Button(boton2,"");
         
         GUI.EndGroup();
 
     }
     
     void CheckButton(Rect boton,int cod) {
         
         switch(cod) {
             case 1:obj=(GameObject) Resources.Load("Cube01");break;
             case 2:obj=(GameObject) Resources.Load("Cube02");break;
         }
         
         ObjectToPlace=obj.transform;
         if(boton.Contains(Event.current.mousePosition)) {
         
             if(Input.GetButtonDown("Fire1")) {
                 Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
                 RaycastHit hit;
                 var layerMask = 1 << 8;
                  
                 if (Physics.Raycast (ray, out hit, Mathf.Infinity, layerMask)) {
                     clone = hit.transform;
                  
                 }else{
                  
                     layerMask = ~layerMask;
                     if (Physics.Raycast (ray, out hit, Mathf.Infinity, layerMask)) {
                         clone = (Transform) Instantiate(ObjectToPlace, hit.point, Quaternion.identity);
                     }    
                 }
             }
         }
              
         if(Input.GetButtonUp("Fire1")) {
             if ((!dest)&&(Physics.Raycast(ray2, out hit2, Mathf.Infinity, layerMask2))) {
                 Destroy(clone.gameObject);
                 dest=true;
             }
             clone=null; // clear clone variable
         }
              
         if(Input.GetButton("Fire1")) {
             if (clone!=null) {
                 ray2 = Camera.main.ScreenPointToRay (Input.mousePosition);
                 layerMask2 = 1 << 8;
                 layerMask2 = ~layerMask2;
                 if (Physics.Raycast (ray2, out hit2, Mathf.Infinity, layerMask2))  {
                     clone.position = hit2.point; 
                 }
                 layerMask2 = 1 << 10;
 
             }
         }
     }    
 }

dont pay attention to the GetButtonUp() function, the destroy was just for testing.

the problem comes now..

my cubes have this script:

 using UnityEngine;
 using System.Collections;
 
 public class Build : MonoBehaviour {
     
     private Material textureColor;
     public Material greenColor;
     
     void Start() {
         textureColor=renderer.material;
         greenColor=new Material (Shader.Find("greenTrans"));
     }
     
     void OnTriggerStay(Collider other) {
         if(other.gameObject.tag==Tags.validSpot) {
             renderer.material = greenColor;
         }
     }
     
     void OnTriggerExit(Collider other) {
         if(other.gameObject.tag==Tags.validSpot) {
             renderer.material=textureColor;
         }
     }
 }

The Cubes have a red material, and i have another material with Transparency/difusse named "greenTrans" but i get an error in runtime:

NullReferenceException UnityEngine.Material..ctor (UnityEngine.Shader shader) (at C:/BuildAgent/work/7535de4ca26c26ac/Runtime/ExportGenerated/Editor/Graphics.cs:1584) Build.Start () (at Assets/Scripts/Build.cs:13)

I know.. i ain't getting the Material from my Assets.

The box needs to collide with a Mesh collider but seems it isnt colliding with it.

Sorry about my english.. i'm trying to be as accurate as i can :(.