Building A Second Life Checkers Game #5

As I mentioned in the previous post, finding the size of a non-root prim from a Second Life Script in the root prim is a pain.

What really makes this a puzzler is that setting the size is pretty darn simple. So I'll look at that first.

I used this same call in the last post to set the position

llSetLinkPrimitiveParams(pieceLinkNum,[PRIM_POSITION, vectPos]);

It is the same call you would use to set the size.

llSetLinkPrimitiveParams(pieceLinkNum,[PRIM_SIZE, vectSize]);

So what's the big problem? Well, there is no llGetLinkPrimitiveParams. What!?! But what about this code to get the location using the object key.

key pieceKey = llGetLinkKey(pieceLinkNum);
list d = llGetObjectDetails(pieceKey,[OBJECT_POS]);
vector vPos = llList2Vector(d,0);

That seems simple enough, except when you look closer at llGetObjectDetails it is not llGetPrimitiveParams. Object details are only a few parameters like name, description and size. Then if you dig for an hour like I did, you find that there is no 'easy' way to get PrimitiveParams given a link number or an object key. You will find it on a Wish List of functions and can just give up until someone finally decides to implement this function that seems so useful, but seems to have been overlooked.

Or you could be like me and figure out a way to get it done, knowing the mantra "There is always a way. There is always a way. There is always a way." I can't seem to find it now, but there was some obscure reference on some wiki page that said it didn't exist and you have to use link messages. So here goes.

Link messages are a way to send messages from one prim to another in a link set (link sets are groups of prims, but group would have been too confusing the Linden folks say). Even though it is frowned upon to have scripts in all the linked objects, this is the only way to get this done.

When I traverse the list of pieces I look for the name of my piece to get the linknum of that piece.

integer i=2;
integer count = llGetNumberOfPrims();
for (;i>count;i++)
{
  string stName = llGetLinkName();
  if (stName == "thepiece")
  {
    // send the link message
    pieceLinkNum = i;
    llMessageLinked(pieceLinkNum,PRIM_SIZE,"43",NULL_KEY);
  }
}

I'm sending PRIM_SIZE as the message number just because I don't have any other messages. In good practice I could probably send a number that is associated with some hair brain scheme I came up with on the fly, but since there is only one message to this prim, anything will do. Normally I would chose 42 since that is the most important number in the universe. Which seems strange in that I did use 43 for the message number that will be used when returning the size to this root prim from the linked prim.

Inside the linked prim, I need to setup a way to receive that message. It is the only thing that script does, which is a good thing. Avoid scripts in linked prims if at all possible.

default
{
    link_message(integer sender_num, integer num, string ret_num, key id)
    {
        if (num==PRIM_SIZE)
        {
            list re_list = llGetPrimitiveParams([PRIM_SIZE]);
            //llOwnerSay("re_list = "+(string)re_list);
            llMessageLinked(LINK_ROOT,(integer)ret_num, re_list, NULL_KEY);
        }
    }    

}

This gets the size using llGetPrimitiveParams([PRIM_SIZE}) which returns the correct value since this is in the prim we want the size from. I then return this size to the LINK_ROOT using the message number that was passed in the link message.

Back to the root prim, here is the code to receive that message.

link_message(integer sender_num, integer num, string list_argument, key id)
    {
        if ((sender_num==pieceLinkNum) && (num==43))
        {
            //llOwnerSay(" list_arg = "+(string) list_argument);
            pieceSize = (vector) list_argument;
            //llOwnerSay("received pieceSize="+(string)pieceSize);
        }
    }    

I save that size into the global variable pieceSize which I can then use in other calculates.

Note, I went through this whole exercise thinking I needed the size of the piece to calculate it's location on the board because I would have to center the piece somewhere. After all that, and a ton of failed attempts I remembered that the origin is automatically the center and I didn't need a single line of this code. Gotta love programming for the amount of time I've wasted in my life. I'm sure I'll use this elsewhere though.