This is the same issue as we had with sculpts. The randomly generated lower LOD meshes are little better than the arbitrary chops applied to the sculpt maps. But we have more power now, with mesh we do not have to accept the manufactured mesh we can submit our own objects.
The LOD generation tool has some strengths here. By manually tweeking the settings we can influence the number of triangles at each level. in the preview window and work out more or less what our target should be for each model and thus set our expectations.
But wait a minute! Look at the Land Impact noted on the left hand side at the bottom.
This object would have a land impact of 9.323 prims, this would be rounded up to 10 prims. The download impact is the highest of the three factors, Download, Physics and Server. Download represents the streaming impact and is for the most part defined by the number of triangles in the object. As mentioned in previous blog entries, triangles in the lower LOD models have a higher cost so by tweaking those settings we can drastically alter the streaming impact and drive down the Land Impact of the model.
In the image above we have altered the Triangle limit parameters for the generator to work with when constructing the lower LODs. By reducing the limits at each level we have managed to bring down the cost to 1.704 (2) prims.
That is much more like it! But look at the quality, the generated medium LOD is OK but its really starting to look a bit shabby. Its at this point where we can take advantage of another one of the benefits that mesh has over sculpts; the ability to define explicit models for each of the LOD levels.
So let's look at our model and start to simplify it. We should keep in mind that the Medium level of detail can be seen from relatively close (the mathematics behind the distances for each LOD level is something I can cover in another blog, but for another explanation, in nice clear terms with no maths in sight, I highly recommend Loki's excellent blog).
On the left is the high LOD model on the right is the reduced detail medium LOD model. The simplifications are quite straight forward. All of the surface details have been removed to give a plain rectangular column, I enlarged it slightly to the same volume as the external dimensions of the ribbing. The cross struts in the shade were simplified to square profiles not circular (Squares are much lower cost than circles) and that was about all. This does not seem like much of a simplification but we will also use the Mesh Studio tool to help us reduce the detail further.
When we generated the high LOD model we simply took the Mesh Studio defaults. Mesh Studio however has options to tune the way in which the prims are translated to mesh along with a number of useful presets. With the script installed in our medium model we can touch it to obtain a menu like the following
The default resolution shown above is 4/24. This tells us that straight paths (edges) will be rendered with 4 vertices whilst curves will have 24 sides. Clicking on the "Resolution" button takes us to a different dialogue where we can tune the resolution. For the medium resolution we will select the Low Poly option. This uses just two points per side to define a straight edge and 16 for a curve. The result for us will be a blockier curve to the lamp shade whilst saving over 1/3 of the vertices.
Before we upload anything we will continue to optimise.
First we will create a low LOD model. At this stage we can expect the model to be being viewed from quite a distance and as such we can take some liberties with the model.
Apart from the bulb, we have removed the cross members on the shade and made the bulb holder itself square. The apertures in the shade itself have been closed in.
In the illustration above you will notice that the inside of the shade is transparent. This is a nother feature of Mesh Studio. All faces that are 100% transparent are assumed to be hidden and will not have mesh generated for them. I have made the assumption that our lamp, when viewed from afar is likely tobe viewed from above and so the inside of the shade will be invisible.
For the final cost savings, we go back to the resolution settings dialogue in Mesh Studio.
This leaves just one final LOD to define. Lowest.
The Lowest LOD pays the highest price for each vertex so we need to keep this as low as possible whilst still serving its purpose. In the case of our lamp I have arbitrarily decided that it will render as noth but a flat plane. As mentioned above I do need to have two texturable surfaces in order for Second Life to accept this model as part of the same mesh as the others.
We are no ready to upload.
You may be surprised to note how many vertices we saved with the simplifications between the High and Medium levels alone. The Land Impact of our model is now down to 1.460, 2 prims still ,but we have defined an elegant set of models for each LOD now, and so we can look at the rest of the upload options.
Next we move on to the physics tab.
Scaling is optional. Once uploaded you can scale the model inworld. The same Land Impact will be gained but by tweaking things in the dialogue we can see how the scale will affect our Land Impact before we upload and in some cases that might send us back to the modelling stage to make some additional tweaks, thus saving an upload fee.
Finally we hit the upload button and our mesh will be transferred to our inworld inventory.
In the next blog, we will look at LOD and compare our new mesh with the old sculpted lamp.