Thoughts on PBR

One of the big issues that had been holding me back from seriously updating my store both in SL and Kitely is the looming PBR update.

PBR itself is an exciting update that I am looking forward to playing with one it hits Opensim. However, I do also foresee some issues. 

As Adobe defines it - "Physically based rendering (PBR), sometimes known as physically based shading (PBS), is a method of shading and rendering that provides a more accurate representation of how light interacts with material properties. Depending on which aspect of the modelling workflow is being discussed, PBS is usually specific to shading concepts while PBR refers to rendering and lighting. Both terms describe the process of representing assets from a physically accurate standpoint."

You can read more here - Adobe Official Site

Image from Adobe

Currently in SL/OS, we tend to "bake" lighting detail into our colour maps, and then shade and highlight them further with Normal and Specular maps if desired. We also fairly recently (a few years ago I think) got the ability to use Emissive (glow) maps.

However with PBR, correct practice is to make your colour/diffuse maps with only colour and noise information. All lighting and shading should be handled by the new PBR material types. 

To illustrate what I mean in a more visual way, here is a quick example taken from my new Sim Surround kits.

Explaining the new complexity rating system for my products.

To better help my customers make informed choices and find it easier to identify the products that they need, I am introducing a new rating system to my listings on Kitely when I roll out my revamped store in the next week(s). 

While I will also endeavour to list the total polycount of each model in a set, some of my sets have several dozen models. In these cases, a range will be given showing the highest and lowest polycounts. 

But also alongside this each product will have a simple rating - Light, Medium and Heavy.

Light - These are the tier of products I offer with the lowest polycounts and using mostly seamless textures. They are great for any purpose, but really shine when you are wanting to build or fill out a large area at the lowest performance cost possible.

Medium - This tier will feature products with slightly higher polygon counts and feature more baked textures. These items can be used fairly extensively in small areas (up to a 3x3 region), but it is not recommended you try to fill several regions exclusively with this level of content. Very often, they will also be designed to refer back to and work alongside Light products as an optional extra level of detail or as a standalone set. 

Heavy - 99% of my content will fall into the previous two categories. However from time to time I reserve the possibility of releasing something crazy. These objects will be fine and fun as a novelty but intended for very limited use and on their own unless clearly stated otherwise. 

.......Hopefully this will all make more sense when my store is back open =D

Obviously, if you are building in a 64x64 region or something nuts, your going to get lag no matter what you do unless you understand what you are doing and take steps to break up your content into manageable "chunks". 

The bottlenecks are the same as ever - 

*Your graphics card

*Your internet connection

*The clunky way SL/OS handles several things relating to LOD, lighting/shadows, textures and off screen geometry culling. 

*The quality of the content you use and your understanding of how to use it. 

Examples of the broken viewer land impact calculations of OS 0.9

 With Opensim 0.9, we got a change in physics engine to ubODE. This has made a number of noticeable improvements (linksets not moving around slightly when you link them anymore is so nice!), but it also broke a lot of mesh content that was made prior to the change.

Most noticeably, mesh with a hole through it (such as doorways and arches) got broken, making them impossible to move past unless you unlink them and make the offending pieces phantom, or re-upload them. 

But arguably the worst change was the total breaking of land impact values shown in the build menu. It seems that now the land impact value shown is inflated by around 3-5 times. The physically larger the mesh becomes, the wider the discrepancy. 

For example, this piece of terrain mesh in Second life is 7 PE/LI. As you can see from me standing on it, it is rather large, so 7PE with full physics is reasonable. 

But in Opensim, it now shows as an eye-watering value of 31. An over-estimate of nearly 4.5 times (7x4.5=31.5)!

As you can see, the LOD settings are exactly the same. The scale is the same. You'll have to take my word that the physics model is too as that info is not shown in the build menu.

But that is not all. Although the number shown is wildly inflated, it does not actually impact on the number of prims used on your sim. Your real land impact will still only count each physical part in a linkset or group of objects. Just as previously.

So......understandably, people are confused. This is also not great for attracting merchants to the space for obvious reasons.

I hope this can be addressed in future OS releases but from what I hear, it wont be. So.....

I think the following example best sums up how well you can trust the land impact calculations as shown in the build menu.....

Here we have a humble mesh plane, subdivided once. 1 LI. And next to it its twin brother, also 1 LI....

So....together, that would be two LI, right?

Dont be foolish! That would make too much sense. Its three, you idiot. (Bear in mind that in SL, each plane would be 0.5 PE = 1 PE total when linked)

Except when it IS two, like those other physically larger, more complex planes that you subdivided THREE times right behind the smaller ones.....

And the problem seems to get more acute the bigger the mesh is. This example shows a dune from my new "world in a box" kit. According to Opensim, its a whopping 239 LI! 

And here it is in SL, where we can see the ACTUAL impact is 20. Which I think is fine for such  huge mesh object with physics. Look how tiny I am on top! :)

So yeah. My new way of explaining Land Impact to people is to look at the data under the "Mesh information" in the "object" tab. 

1 sculpted prim = 256 tris. I think that gives most people at least a vague calculus to judge if a mesh is "worth it" or not.