Tips Needed To Maximise Mesh Detail Whilst Minimising Land Impact

[Moco Scribe]

I am enjoying my new building apprenticeship developing my Mesh skills and knowledge and feel that I have made some progress.

However I am now stuck, quite stuck. Although I am probably at the stage where I can create most of the things I would like in my store no matter what I do the Land Impact for some objects remains stubbornly high.  I use Strata 3D to design most things and lower the polygon complexity at every stage to keep LI as low as possible and when uploading create a separate physics object and set the physics and LOD etc in the most optimum way. But the bench I designed recently still uploads as 21 LI when I see similar chairs on the Marketplace at 3 LI. Not to mention the chandelier at 300....but that's a whole other story!

Any other tips and where am I going wrong....

Moco Homes Emporium On The Marketplace

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[Chic Aeon]

Oh my! 

There are three parts to the final weight of a mesh object in SL. Server, Physics and Download. You need to look at each part and see which is the problematic one.

In the case of smaller items like furniture, it is most often "best" to JOIN (this is a Blender term and not sure how that translates) objects before exporting. So that they are ONE mesh object, not a linkset when brought into world. Hence no unlinking. That won't work if you need to turn on a light bulb or hinged doors to open of course, just generally.   This would be the SERVER part of the three. So an umbrella for example would be ONE mesh object with a sever cost of .5.

 

A chandelier doesn't really need much physics so you can use a plain cube for the physics LODs and it will surround the item in totality. Again, if you have a chair that you want to be able to sit on without a pose in the chair -- you will then NEED physics. So the CUBE is a general hint and one many furniture makers use since poses are most often part of the design.  That's the PHYSICS part.

The download section of the three looks at complexity. Remember that for furniture that will be inside and not seen from a long distance there is no reason to have it upload so it can hold its shape ALL THE WAY across a sim. Test a lot on the beta grid to get an idea of what is acceptable and what is not. Some folks design for those that have LODs set to 2 (amazingly the default even with a good computer that easily runs shadows on ultra with everything on ) and some for those at 4. That is something you need to decide but it will affect the land impact.

 

If you put in a screenshot of an upload panel for others to look at, they can most likely give you more tips and see instantly where you need to make changes. And to be fair, your idea of low poly topology might not really be as low as it needs to be. No one can tell without some screenshots. I went to your Marketplace site but couldn't see what was mesh and what not -- easily anyway as I am tired and heading back to bed.

 

Good luck. When you "get it", you'll have it. That's the good news.

Houses of course are a different story with different "hints" .

 

 

[Moco Scribe]

Hi Chic,

Thanks for the overview and great idea about the screenshots so I will get that organised. I'll use the example of the mesh chandelier I recently created there's a picture on my latest blog post. 

Houses and mesh I'm ok and now looking at furniture as the final frontier for getting low LI!

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[Indigo Mertel]

Take a look at this blog post: Mesh: Understanding Land Impact » Sculpt Blender http://bit.ly/16nsWaH

You may be already familiar with what is explained in the post, but just in case...

 

[Drongle McMahon]

I went and had a look...

Bench on veranda: Server weight 5.7(Uh? Did they change the rules here? I thought it had to be an integer*0.5 !). So it can't go less than 6 LI unless you join the meshes. For now, downloas weight is 6.9, which is hihger, but there's plenty of opportunity for reducing this. First, the legs and the curved part of the back have some faces subdivided into three when they don't need to be. Second, there are lots of faces on buried ends of various pieces, which can all be removed. Lod behavior is a bit odd, with the arms disappearing. This may be solved by joining. The LI in the end will depend on the low LOD mesh. The other bench, with the cushions is so high because the cusions and blanket have many more triangles than they really need.

House: Generally very nice, but the window frames have very poor LOD behavior-almost as bad a sculpties. For the round windows, this happens even while you are inside the house (because they are small).  This was with renderVolumeLODFactor = 2.0, which is the default for High graphics settings. Same problem with the front door frame, where some of the small bars are separate meshes, so that they switch LOD at very small distances. Do these really ness to be that much rounded?

Windows are very easy to make perfect LODs at low LI because you can use simple planes with alpha texture for the low LODs (you hide it on a hidden triangle at the high LOD and put extra hidden triangles for the high LOD textures on the low LOD). I would strongly recommend using this technique for all your windows. It will improve LOD behavior and reduce LI. You can make the switch further away, if you want, by joining some windowns to make them bigger, although that would likely also increase LI. The round windows also look like they have many more triangles than they need.

There are also lots of beams in the house with sides subdivided into three, as in the bench (are these made from prims?), and lots of hidden ends with unecessary caps (eg, bannister rods). Finally, there are some rounded things that seem to be using more triangles tyhan they are worth; for example, the fireplace and the chandelier chain. Are these already making use of smooth shading, rather thyan subdivision, to save triangles and LI?

Eta: By the way, I have used the window low-LOD-alpha technique on a LI=1 bench too. First the slatted back and base are replaced by an alpha. If has the legs and uprights too, but they stay hidden under the solid ones.  Then at the next LOD, the legs disappear so it's only the simple boxes with alpha. If I can find the meshes, I'll upload some pictures.

Here's a picture. Four LODs in orange, physics in yellow. One of the low LOD textures on the right. Probably should have been smaller, 128x128. Lost the one for the seat part. You can reduce LI further by skipping the second LOD.

[Moco Scribe]

Thanks Drongle that is really detailed and very useful. I'm going to change the windows they were bugging me before and I did suspect that the LOD was too low but they didn't always wrong just sometimes. I didn't really understand what you meant about low and high hidden triangles for the windows so could do with some more clarification if you don't mind.

But great advice, you are clearly a Jedi Knight of Mesh optimisation : )

As I said earlier I am less worried about the house simply because overall it is coming in at quite a low land impact. But I have more of a problem getting more rounded organic objects such as the chandelier lower - did you take a look at that too - she asks meekly?

Below is a scenario which sort of illustrates what I'm trying to get to grips with, any further advice greatly appreciated, hopefully you can see the detail in the slides;

 

 

 

 

 

[Moco Scribe]

Thanks indigo I've probably read it already but no harm in having another look!

[Moco Scribe]

Erm...showing my ignorance here...(again) but what's an LOD texture??

Gulps and waits for laughing to subside, sips her tea and waits for advice.

[Drongle McMahon]

Things like that cable are the devil. Looks like you vave a six-vertex cross section. That could be reduced to five, and maybe the plugs could use fewer too. I can't see what the structure of the pins are, but they look like they are too detailed too. You really have to make the lower LODs by hand to avoid those artefacts, probably just removing alternate (or more) loops around the cables at each step. However, at this size, the lowest LOD will be by far the most important for LI. I'm assuming this is nearly flat. In that case, the lowest LOD (or maybe even the lowest two) could be just a flat plane with a picture of the cable on a transparent background. That will give very low LI (since you already have good physics).

You do have to have the same number of materials in the meshes at all LODs. So you have to add a small triangle, maybe inside a plug, to carry the low LOD cable picture in the high LOD mesh. That's the hidden triangle. Similarly, you have to have triangles in the low LODs to carry the textures used in the high LOD. In this case, they can be facing downwards so that the textures won't be seen. It was those textures hiding on these extra triangles that I was calling the low LOD tecture etc. ([low-LOD] texture, not low [LOD texture[).

[Aquila Kytori]

Hi 

First and probably most importantly NEVER EVER put a plug on both ends of a mains electric cable ! Always a Plug one end and a Socket the other .  

As others have said the best ways to reduce LI is to use less vertices and work on the LODs . For something as thin as an electric cable a cross section of only 4 vertices is probably enough . When set to smooth shading its only noticeable when you zoom in very close.

[Moco Scribe]

Thanks again Drongle

[Moco Scribe]

Thanks for the detailed reply Aquila, I am envious of your low LI cable.

 

No idea why I added the second plug, I obviously got carried away with building!

 

I noticed that you selected 'use lod above for the lower lods what's the advantage of using that over 'generate'?

 

Thanks again

[Kwakkelde Kwak]

Besides all the improvements that can be done by remodeling and optimising the upload settings, I think there's one thing that can make a huge difference.

Some 3D programs, like Sketchup, export all faces twice. Once for the "normal side", once for the other side. This way a flat plane has a backside. The problem is you do not need the inside on any object with volume, since you'll never see it. Going by the amount of vertices on the cable, I suspect this is happening though. The cable is 97x6=582 vertices if I didn't miss a loop somewhere. I don't know how the plugs are modeled, but 3000 looks very high going by the cable itself.

What you can do to test this is exporting a single triangle or quad. If it has a backside in SL, all your models can be halved in geometry. I'm not sure how to fix this in Blender, I'm sure someone else does. In 3ds Max it takes only a couple of clicks with an object this simple.

[Aquila Kytori]

As Drongle pointed out for a small item like this its the lowest Lod that is going to effect the LI a lot. Using the highest LOD for the first 3 levels  is the "cheap and nasty" way of getting good LOD's . Its the lazy way of doing it , but not ideal for lowering lag because its using vertices / details that won't really be seen at a distance but still have to be calculated.

Ideally you should do as Drongle said, manually remove edge loops for the lower LODS and use a simple image for the lowest (or even lowest 2) LOD('s).

[Moco Scribe]

Thanks

Can I just upload the image for the lowest 2 lods via the 'upload file option' and I should use this only for small items not needed to be visible at a distance. These may seem like basic questions but appreciate your help!

 

[Moco Scribe]

Great thanks for the tips

 

I don't use blender it unfortunately doesn't agree with me but will check the 3d system I use.

[Kwakkelde Kwak]

I understand you do not use Blender, but if your program of choice doesn't allow you to export single sided (like Sketchup) it seems to be the logical choice. You'd only need Blender to export the dae or to remove the inside then export as dae.

If your program has a single sided modeling or export setting, you should use that of course.

[Aquila Kytori]

---

Moco Scribe wrote:

 

Can I just upload the image for the lowest 2 lods via the 'upload file option'

---

No,

For the lowest 2 LOD's you have to create a separate mesh object . This Low LOD mesh object will me a simple plane the same dimensions as your cable. This Plane will need to have its own material and also you need  a triangle for each material already used in the original mesh. Each LOD mesh has to contain the exact same materials as all the others otherwise you will get an Error in the uploader.

So you will need to Add a "Hidden " triangle in the original high LOD mesh to hold the material for the Low LOD mesh.

Example : I used 3 materials for my cable . The actual cable part I assigned a red texture called "Cable" , the plug/socket I gave a dark grey colour and named that material " plug" and the prongs of the plug white and called it "metal".

I added a Triangle and gave that its own material called "image"

Next I create the Low LOD mesh . This is a completely separate mesh from the original . This Low LOD mesh is a simple plane and assigned the "image" material. Because all LOD meshes must contain the same materials I next add 3 little triangles and give each of these one of the other materials.

Next I need an image to put on that Low LOD Plane once it is uploaded into SL, so I simply render an image of the cable in blender and save that with its  transparent background .

Now I have 4 different files for the mesh cable

1: High LOD mesh .dae  ( thats the original cable with the extra triangle )

2: Low LOD mesh.dae   ( that's the simple Plane mesh with the 3 extra triangles )

3: Cable Physics.dae     ( a cube encompassing the high LOD mesh which is used for the Physics  shape in the uploader)

4: Cable Image.png       ( the image that will be applied to the triangle and so appear on the Low LOD mesh plane )

The 3 .dae files are used in the mesh Uploader as shown below :

And the .png Image for the Low LOD texture is uploaded as you would any normal texture and then once the cable mesh has been rezzed inworld you need to edit it and check "select by face" then select that triangle and give it the Low LOD Image texture.

 Note : Normally you would "hide" the extra triangles so they are not visible when the mesh is rezzed . In this example you could hide that triangle by making it a lot smaller and placing it underneath one of the plugs , or because the cable would normally be flat on a ground surface you could simply flip its normals 

            Because the Lowest LOD now has far fewer triangles the LI has been reduced further.

The best is to experiment with a very simple mesh untill you understand what is going on 

 

[Drongle McMahon]

Excellent description from Aquila. One small point to add - if the triangle for the low LOD texture is hidden inside the high LOD mesh, you can't select it to put the texture on it. There are a couple of ways round this. Easiest is to first texture the whole thing with the low LOD texture, and then apply the other textures to selected faces. Better (works for multiple low LOD textures), you can use Advanced->Show degug settings to set renderVolumeLODFactor to 0. Then the lowest LOD will be visible and you can select it or drop the texture on it. Then reset the RenderVolumeLODFactor. Finally, you can use a script, if you know how to do that.

[Moco Scribe]

Aquila 

That was an excellent overview - thanks so much for your time in pulling this together. if you have a blog publish it on there as I've come across many explanations of this technique but none as clear.

I'll have to have a think as to when best to use it as it is a lot of work just for a cable but it will come in very useful for so many other things.

I'm excited now but my brain feels fried after all the re-building I've done today, changing all the windows on my new build cottage and many other fixes...need a lie down...now where's the wine...

 

 

[Moco Scribe]

Drongle is there no end to your knowledge in this area! 

I'm glad I asked the question as I've learned loads. I never really knew about the hidden triangles or textures despite reading a lot of stuff on Mesh.

 

Thanks again