U Lookin at Me?

I'm hopeless when it comes to rotations & vectors. What I'm after is a way of working out if an avatar is facing a prim. I'm sure there's a way to calculate this, using an avatar's position and rotation, but I have no idea how to do it.

I'll give L$500 to anyone who can give me the calculations (in LSL) to work this out. I don't need an entire script, just the calculations necessary to work this out. The prim that the script will be in will move around, so please keep this in mind. Use the below Sensor event if you want, or not.

sensor(integer num_detected)
{
	integer i;
	for (i = 0; i< num_detected; ++i)
	{
		vector pos = llDetectedPos(i);
		rotation rot = llDetectedRot(i);
		
		//calculate if avatar is facing me.
		
		if (FACING)
			llSetColor(<1,1,1>,ALL_SIDES);
		else
			llSetColor(<0,0,0>,ALL_SIDES);
	}
}

If noone can help with this, but can provide a link to somewhere that explains how to do this that helps me I'll pay you L$250

I don't want your money. There are few ways to skin this cat. One approximation is to take the dot product of the avatar to the target, and the avatar's direction. If it's greater than some threshold, we'll say they're facing your prim.

The following is an uncompiled code that hopefully illustrates what I'm trying to do. (forgive me if I use an API that doesn't exist

// Play around with this value
float threshold  = .9;

sensor(integer num_detected)
{
	integer i;
	for (i = 0; i< num_detected; ++i)
	{
		vector pos = llDetectedPos(i);
		rotation rot = llDetectedRot(i);

		//calculate if avatar is facing me.
		vector av_fwd = llVecNorm( llRot2Fwd( rot ) );
                vector av2prim = llVecNorm( llGetPos() - pos );

                if ( llVecMag(av_fwd*av2prim) > threshold )
                     FACING = TRUE;

		if (FACING)
			llSetColor(<1,1,1>,ALL_SIDES);
		else
			llSetColor(<0,0,0>,ALL_SIDES);
	}
}

I believe Alondria has something more sophisticated that will actually calculate the intersection of your view and the prim face.

Thanks Fran!!! *hugs*
I'll try this as soon as I get home tonight. I had no idea it would be so simple, well not simple but only 3 lines. I don't understand it, but as long as it works I'm happy hehe. I'd love to understand it, but I can't afford for my brain to explode at the moment.

I should have just asked you in the first place (but I know how busy you are).

Thanks again!!!

There was one small error in the script posted by Fran, so I'll post the correction incase anyone else want to use this (Fran worked out the problem not me).

// Play around with this value
float threshold  = .9;

sensor(integer num_detected)
{
	integer i;
	for (i = 0; i< num_detected; ++i)
	{
		vector pos = llDetectedPos(i);
		rotation rot = llDetectedRot(i);

		//calculate if avatar is facing me.
		vector av_fwd = llVecNorm( llRot2Fwd( rot ) );
                vector av2prim = llVecNorm( llGetPos() - pos );

                if ( av_fwd*av2prim > threshold )
                     FACING = TRUE;

		if (FACING)
			llSetColor(<1,1,1>,ALL_SIDES);
		else
			llSetColor(<0,0,0>,ALL_SIDES);
	}
}

The line: if ( llVecMag(av_fwd*av2prim) > threshold )
was changed to: if ( av_fwd*av2prim > threshold )

Thanks again Fran!

Huh... looks like the wiki's description of vector * vector was a little incorrect, then. No wonder I was confused.

Perhaps someone who understand vectors better than I should update the wiki for this..

Done.

sorry about that; when i was writing up the table i wasn't testing everything in SL as i was doing it... Was before I started playing SL in window mode.

We still love you, Strife.