This script handles turning the phantom property on and off.

// Phantom door LSL script #1
// Handles the touch event.

// Processing for the script when it first starts up

default {
    // What we do when we first enter this state

    state_entry() {
        state closed;                       // Move to the closed state
    }
}

// Processing for the script when it is in the closed state

state closed {
    // What we do when we first enter this state

    state_entry() {
        llSetStatus(STATUS_PHANTOM,FALSE);  // Turn off phantom property
    }

    // What we do when the door is clicked ("touched") with the mouse

    touch_start(integer total_number) {
        state open;                         // Move to the open state
    }
}

// Processing for the script when it is in the open state

state open {
    // What we do when we first enter this state

    state_entry() {
        llSetStatus(STATUS_PHANTOM,TRUE);   // Turn on phantom property
    }

    // What we do when the door is clicked ("touched") with the mouse

    touch_start(integer total_number) {
        state closed;                       // Move to the closed state
    }
}

When the script starts, we move into the "closed" state, which here means that the door is solid, not phantom. When the closed state begins, we set the phantom status of the door to false via

        llSetStatus(STATUS_PHANTOM,FALSE);  // Turn off phantom property

When the closed solid door is touched, that is, clicked with the mouse, we move to the "open" state. When the open state begins, we set the phantom status of the door to true via

        llSetStatus(STATUS_PHANTOM,TRUE);   // Turn on phantom property

If the open phantom door is clicked, we move to the closed solid state. And so on and so on.

This is pretty much the most basic script on an object that toggles some behavior when the object is clicked. It is similar to the first sliding door script, but there we needed to save some extra information about the previous position of the door and know how much to move it. All the real action in this script takes place in the state_entry functions for the open and closed states.

It is in these functions where we could add some kind of state indicator to show whether the door is solid or phantom. One possibility is that we create a separate light over the door that is green when the door is phantom and red when solid. That's a bit complicated at this point, so let's go with a simpler plan.

At the beginning of this section I referred to the phantom property as being ghostly because avatars can just pass right through. How about we make the door partially transparent when it is phantom and then non-transparent when it is solid?

If we make the door completely transparent, people might not know that it is even there. If we don't make it transparent enough, then they won't be able to notice any real difference. What value of alpha will work for us? In this particular case, using 0.75 seems about right and that's what is pictured to the right. For your particular door, you should experiment until you get something that works for your situation. Remember to look at it in different lighting conditions.

There's a technical point I need to make here that you might want to skip on first reading. The alpha value applies to each side in each prim in your object. In a one-prim door, there are 6 sides: front, back, top, bottom, left side, and right side. If we link in more prims, we must deal with each of their sides as well. LSL makes it easy to set the alpha values for all the sides on all the prims at once. However, it makes no sense to ask for THE single alpha for an object, because there is one for each contained side. They might happen to be all the same, but in the general case they will be different.

In our example here I'm going to make a significant simplifying assumption: we can set the alpha value to 1.0 for every side in every linked prim when we want the door to be solid.

I'll do this by changing the alpha  value for the door. When this is set to 0.0, we have have complete transparency. When it is 1.0, we have no transparency other than what might be in the textures themselves.

Here is the version of our script that includes transparency:

// Phantom door LSL script #2
// Handles the touch event.
// Handles partial transparency when the door is in phantom mode.

// Processing for the script when it first starts up

float alpha = 0.75;                         // alpha value for partial transparency
                                            // of the door when in phantom mode.
                                            // 1.0 is solid, 0.0 is transparent.

default {
    // What we do when we first enter this state

    state_entry() {
        state closed;                       // Move to the closed state
    }
}

// Processing for the script when it is in the closed state

state closed {
    // What we do when we first enter this state

    state_entry() {
        llSetStatus(STATUS_PHANTOM,FALSE);  // Turn off phantom property
        
        llSetLinkAlpha(LINK_SET,            // Turn off transparency 
          1.0, ALL_SIDES);
    }

    // What we do when the door is clicked ("touched") with the mouse

    touch_start(integer total_number) {
        state open;                         // Move to the open state
    }
}

// Processing for the script when it is in the open state

state open {
    // What we do when we first enter this state

    state_entry() {
        llSetStatus(STATUS_PHANTOM,TRUE);   // Turn on phantom property
 
        llSetLinkAlpha(LINK_SET,            // Turn on partial transparency 
          alpha, ALL_SIDES);       
    }

    // What we do when the door is clicked ("touched") with the mouse

    touch_start(integer total_number) {
        state closed;                       // Move to the closed state
    }
}

I put the declaration and definition of alpha at the top of the script so that it can be easily found and changed. When programming it's important to do this and not embed magic numbers like "0.75" somewhere in the code. They can be hard to find and change, especially if a lot of time goes by or someone other than the original author is trying to use the script.

float alpha = 0.75;                         // alpha value for partial transparency
                                            // of the door when in phantom mode.
                                            // 1.0 is solid, 0.0 is transparent.

When the door is closed, that is, solid, we turn off transparency using llSetLinkAlpha :

        llSetLinkAlpha(LINK_SET,            // Turn off transparency 
          1.0, ALL_SIDES);

        llSetLinkAlpha(LINK_SET,            // Turn on partial transparency 
          alpha, ALL_SIDES);