Creating a toolbar with toggleable buttons

You need to use an array of booleans to back up a row of normal buttons.

If the boolean for the corresponding button is set true, then that button should be marked active. There are several ways you can do this. One way is to create a GUISkin and two styles, then set the values there. Or if you need to have it in a custom editor, then you might have to make three custom styles, inactiveButton and activeButton and a normalButton. normalButton is just a temp variable to tell the buttons. InactiveButton has the normal textures for its state, and activeButton has them inversed, i.e. looks like it's being pressed when it's not. (the values you need to modify in the GUIStyles are normal and active. ). You'll want to probably make your own textures, the default ones aren't very impressive. You can change it by accessing the background field in the styles.

Because what I just wrote is pretty incoherent, here's something I hacked together to give you an idea:

     GUIStyle inActiveButton;
     GUIStyle activeButton;
     GUIStyle buttonStyle;
     bool[] boolArray = {false,false};
     void OnGUI(){
         inActiveButton = new GUIStyle(GUI.skin.button);
         activeButton = new GUIStyle(GUI.skin.button);
         buttonStyle = new GUIStyle(GUI.skin.button);        
         GUI.skin.button.margin = new RectOffset(0,0,0,0);
         GUILayout.BeginHorizontal();
         for(int i=0;i<2;i++){
             if(boolArray[i] == true){
                 activeButton.normal = GUI.skin.button.active;
                 buttonStyle = activeButton;
             }
             else
                 buttonStyle = inActiveButton;
             
             if(GUILayout.Button(i.ToString (),buttonStyle)){
                 boolArray[i] = !boolArray[i];
             }
         }
         GUILayout.EndHorizontal();
     }