llCastRay

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/LSL

CastRay

llCastRay

Summary

Function: list llCastRay( Vector start, Vector end, list options );

	Forced Delay
	Energy

Description TBD
Returns a list consisting of a three values for each hit:

• UUID
• Link number
• Hit position

• Vector	start	–	starting location
• Vector	end	–	ending location
• list	options	–	Consists of one or more of: RC_REJECT_TYPES followed by an integer "filter" described below. RC_DATA_FLAGS followed by an integer "flags" described below. RC_MAX_HITS followed by an integer specifying the max number of hits to return. RC_DETECT_PHANTOM followed by a boolean integer (default 0, FALSE).

Constant	Default Value	Description
RC_REJECT_TYPES	0
RC_DATA_FLAGS	0
RC_MAX_HITS	1	Maximum number of hits to return. Maximum value is 256--To avoid performance issues, keep it small.
RC_DETECT_PHANTOM	0, FALSE	Set to TRUE (or nonzero) to detect phantom AND volume detect objects. It is not possible to detect only phantom objects or only volume detect objects. If set to TRUE, phantom and volume detect objects will always be detected, even if RC_REJECT_NONPHYSICAL and RC_REJECT_PHYSICAL are set in RC_REJECT_TYPES.

Caveats

Ray casts are throttled by the amount of time actually taken to perform the cast. Each region is allotted a 2ms pool, divided proportionally over parcels the same way prim limits are. Each agent is allotted 100us. All scripts in attachments and, objects on which an avatar is seated, use the agent pool whereas all scripts use the parcel pool. A ray cast can be performed if at least 30us of raycast time remain in the appropriate pool. If there is insufficient time remaining, RCERR_CAST_TIME_EXCEEDED is returned as the status code. The exact time used by the ray cast is measured when it is performed and that number (in microseconds) is subtracted from the pool. (The time remaining can be a negative number.) Over time, the pool is automatically replenished (at a rate of 25% of the max time per frame).

For example, if you start out with 100us and perform a 50us raycast, 50us will be remain. If you then a 70us raycast during the same frame, you will have -20us remaining. Subsequent calls to llCastRay that frame will fail with status code RCERR_CAST_TIME_EXCEEDED. At the start of the next frame, you will have 5us available (25us are restored each frame) and any attempt to call llCastRay will again fail as you need 30us to execute a raycast. One frame after that, 30us will be available and a raycast can once again be performed.

This method of throttling puts the scripter "closer to the machine". That is, you're only being charged for what you use, and more efficient raycast techniques will automatically be charged less than less efficient ones. The exact throttle values are subject to change at any time before release to the main grid.

Tips for Efficient Raycasts:

• Keep the max number of hits returned as small as possible
• Set as many RC_REJECT_TYPES as possible (of factors you can control, this will likely have the largest impact). For example, if you only want to know where the nearest agent is along a ray, use RC_REJECT_LAND

Examples

<lsl> integer filter = 0;

default {

   state_entry()
   {
       llSay(0, "Hello, Avatar!");
   }

   touch_start(integer total_number)
   {
       vector start = llGetPos();
       vector end = start - <0,-25,0>;
       
       if ( filter > 8 )
       {
           filter = 0;
       }
       
       llOwnerSay("Filter " + (string)filter);

       list results = llCastRay(start, end, [RC_REJECT_TYPES, filter, RC_MAX_HITS, 4] );
       
       integer hitNum = 0;
       // Handle error conditions here by checking llList2Integer(results, -1) >= 0
       for ( hitNum = 0; hitNum < llList2Integer(results, -1); hitNum++ )
       {
           // Stride is 2 because we didn't request normals or link numbers
           key uuid = llList2Key(results, 2*hitNum);
           string name;
           if ( uuid == NULL_KEY )
           {
               name = "Land";
           }                
           else
           {
               name = llKey2Name(uuid);
           }
           llOwnerSay("Hit " + name);
       }
       
       filter += 1;
   }

}

</lsl>

Notes

Use llDumpList2String to see what the output looks like when you try a new set of flags.

Ideas for uses:

• Weapons. I'm personally praying that llCastRay will make simulated projectile weapons essentially obsolete in SL. They're horrible for performance. Ray casts FTW!
• AI objects
• Vehicles. Try simulating the wheels using raycasts. Not sure if LSL will be fast enough, but I'd love for someone to try and report back.
• A very slow, but kind of cool, ray tracer that could build an image of a sim by casting rays around and determining the color of the thing they hit and modifying a child prim in a display object to have that color...or something. I'd really love to see someone build something like this, actually.

Deep Notes

Signature
function list llCastRay( Vector start, Vector end, list options );