Megaprims

I have heard here and there that megaprims negatively impact performance in SL. Is this a fact? If so does anyone know any details about this (i.e. how much of a drag they cause, is it relative to the size or shape of the megaprim, etc.). Is there a possibility that LL will forbid their use at some point (or is this even possible)?

Also, I would also be interested to hear what approach other builders take towards using megaprims.

Thanks in advance!

If they're not physical and they're not interacting with lots of physical stuff, don't worry about it. Really.

It depends whom you ask. Some claim that megaprims are detrimental to the way in which sims communicate with each other, because they can be "seen" by neighboring sims from further distances than can normal prims. Others say this is just a technicality, which has no noticeable effect. Conventional wisdom is that megaprims should always be phantom, so as not to tax the physics engine, but then there are those who profess that improvements to Havok 4 implementation have rendered that precaution unnecessary. Nobody seems to know for sure. Even Lindens appear to disagree on what's what with megaprims.

Since all we've got to go on is a definite maybe, my feeling has always been just use them sparingly. If a megaprim or two will solve a problem you can't otherwise solve, then go for it. Just be careful not to overlap other people's property with them, don't use too many of them, keep them phantom just to be on the safe side, and everything should be fine. But as I said, that's just a feeling. I have no idea what's actually happening with/from them behind the scenes.

"Also, I would also be interested to hear what approach other builders take towards using megaprims."

I dont use them in for sale builds simply because they can`t be mod without reverting back to a 10m x 10m. If it`s a one off custom build and a customer wants them for prim saving , I normally keep them in a seperate linkset and forewarn the customer what happens if they try and mod.

Thanks for the responses. Good tip about modifying - I had not thought about that aspect. I have generally avoided them in the past because that are not standard, so my main reason for posting was trying to get a better understanding.

However, the thing that brought them up again is that I am working with a curved design for a new structure I want to create. Basically I need a some segments out of a large circle. I am able to create these by taking a megaprim box converting it to a cylinder and then using the hollow and path cut options to create my segment. This is pretty straightforward although I am somewhat bound to the available sizes for my outer radius. The alternative (at least the one I came up with!) is to use tapered cubes to create wedges. These wedges can then be connected to create the large circle I need. Assuming you want to avoid seams (which I do), this approach requires a fair amount of calculating (which does not bother me). Connecting the wedges to create a true circle is somewhat painstaking, although once this is accomplished the new megashape can be reused so the work may be worth it. The only other thing is that this does not create a true circle but neither does SL for that matter.

If you want to make a faceted circle out of cubes, there are a number of scripted tools available that will automate the process. Cadroe Murphy's Shapemaker is a good freebie.

I've also got a compass-like technique I developed years ago, but I don't think I've ever written about, which allows for making circles of any size in just a minute or two. Here it is:

1. Decide how many facets you want your circle to have. I usually go with 24, since that's the number of facets an SL cylinder has. People in SL are used to thinking of 24-sided objects as "round".

2. Simple math tells us that if there are 24 facets, then they all must be rotated in multiples of 15 degrees. Remember that number.

3. Create a cube to serve as your first facet. For now, make it 10M wide. We'll end up shortening it in a minute, but for now 10 will be the easiest thing to work with.

4. To keep the math easy for this example, let's say we want our diameter to be 20M. That means the center point will be 10M from the edge. Rez another cube (or any shape you want) 10M from the first cube. Name it CenterPrim. Make sure the two are aligned on-center with each other.

5. Link the two prims together, so that the CenterPrim is the parent.

6. Shift-drag to leave a copy behind, and then press ctrl-Z to undo the movement.

7. Now, in the editor, rotate the linkset by 15 degrees. DO NOT try to rotate via the onscreen manipulator, or the object won't rotate around the right pivot point. When you use the numbers in the editor, the pivot is the center of the root prim. When you use the manipulator, the pivot is the geometric center of the entire linkset. For this to work, CenterPrim must be the pivot.

8. You'll now see the two edge prims are intersecting each other at a 15 degree angle. The only problem is they're way too long right now. So shorten them both by the same amount, until they just touch at the corners. This is really fast and easy, if you turn on Stretch Both Sides, zoom in on one end of one prim, and just move that end with the stretch tool, until it hits the edge of the other one. Then just set the second one's size to be the same as the first one, and you're good to go.

9. Now, repeat steps 6 and 7 twenty-two more times, and you'll have a complete circle.

10. Select all the objects, unlink everything, and delete all the center prims, leaving just the edge prims in place. You've now got a 20M circle, with 24 facets.


This procedure will work for any size circle you'd care to make, within link distance. I make circles this way all the time. It takes about 30 seconds, tops, once you've gotten used to the work-flow. Shapemaker still has an advantage in that it can create circles that are larger than link-distance-radius. But it's pretty rare you ever have to go that big.

If you're a purist at heart, automation can sometuimes feel like cheating. But this "compass method" is done entirely by hand, so it won't offend that particular sensibility, if you do have it.


By the way, this method will also work with arcs constructed out of cut cylinders, if you want a smoother look than you'd get with cubes.

I built half my shopping centre with them, never had any major problems over last 2 years. Non phantom is fine, Physical creats some dramas