Empty spaces in buttons are detected by mouse

I played a bit and came up with a example. Put the following two images in your Assets folder. Both need to be imported in a format that supports transparency, and the mask image needs to be read/write enabled:

• Create a material using the buttons.png texture. The Unlit/Transparent shader would work well.

• Create a vertical plane and attach the material.

• Add the following script.

• Drag and drop the buttons_mask texture onto the tex variable.

• In the inspector, set the size of the color array to 6 and enter the following colors: (255,0,0), (0,255,0), (0,0,255), (255,255,0), (255,0,255), (0,0,255).

  ---

  using UnityEngine; using System.Collections;

  public class Buttons : $$anonymous$$onoBehaviour {

     public Color[] colors;
       public Texture2D tex;
   
       void Update () {
           Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
           RaycastHit hit;
           if (Input.Get$$anonymous$$ouseButtonDown(0) && Physics.Raycast (ray, out hit) && hit.collider.name == "Buttons") {
               Color pixColor = tex.GetPixelBilinear(hit.textureCoord.x, hit.textureCoord.y);
               if (pixColor.a < 0.5f) {
                   Debug.Log ("Hit an transparent area");    
                   return;
               }
               for (int i = 0; i < colors.Length; i++) {
                   Color c = (colors[i] - pixColor);
                   Vector3 v = new Vector3(c.r,c.g,c.b);
                   if (v.sqr$$anonymous$$agnitude < 0.1f) {
                       Debug.Log ("Button " + i + " pressed");
                   }
               }
               
           }
       
       }
   }
  
  

You could do this using GUI by placing the texture in a box and using GetLastRect (or know the rectangle if you aren't using GUILayout) and then work out which coordinates to put into GetPixelBilinear by working out the current mouse position as a proportion of the width and height of that button rectangle.

@whydoidoit - nice idea.
@mh4 - here is a bit of sample code implementing the idea:

 using UnityEngine;
 using System.Collections;
 
 public class Buttons2 : $$anonymous$$onoBehaviour {
     
     public Color[] colors;
     public Texture2D tex;
     public Texture2D tex$$anonymous$$ask;
     private Rect rect;
     private float x = 150;
     private float y = 125;
     
     void Start() {
         rect = new Rect(x,y, tex.width, tex.height);
     }
     
     void OnGUI() {
         Event e = Event.current;
         
         if (e.type == EventType.$$anonymous$$ouseDown && rect.Contains(e.mousePosition)) {
             Debug.Log ("Inside");
             Vector2 v2 = e.mousePosition;
             v2.x -= x;
             v2.y -= y;
             float u = v2.x/rect.width;
             float v = 1.0f - v2.y/rect.height;
             
             Color pixColor = tex$$anonymous$$ask.GetPixelBilinear(u, v);
             if (pixColor.a < 0.5f) {
                 Debug.Log ("Hit an transparent area");    
                 return;
             }
             for (int i = 0; i < colors.Length; i++) {
                 Color c = (colors[i] - pixColor);
                 Vector3 v2b = new Vector3(c.r,c.g,c.b);
                 if (v2b.sqr$$anonymous$$agnitude < 0.1f) {
                     Debug.Log ("Button " + i + " pressed");
                 }
             }            
         }
         GUI.DrawTexture (rect, tex);
     }
 }