SKYRIMSE Optimizing 3D LOD models

[thismysafespace]

Hi!

I'm have made 3D LODs and I want to create a "performance version" of the 3D LODs. I noticed that the Step Modifications team has created plenty of 3D LODs for various tree mods with this option. I'm unsure where to start in this process of optimizing the tree models. So far, as you can imagine, the decimate modifier in blender seems to be greatly lowering poly count but at the cost of a deteriorated model. I have seen the term "flat trunk models", but am also unsure of how to do this or what it means. Does this refer to the trunk after running it through hybrid.bat? Any advice on where to start or what tools to use? Also, should I only concern myself with optimizing the trunks or would it be wise to include optimized crowns?

Thank you in advance for any help!!

[DoubleYou]

Hybrids are made by splitting the crown from the trunk and making a billboard of the trunk that gets attached to the crown. 

@z929669 made a guide for how he creates the 3d hybrids here: https://stepmodifications.org/wiki/Guide:Creating_Tree_LOD_Models

If you use Decimate, it will, like you found, just make an ugly model. If you want to optimize the trunk for 3d, it is probably easiest to rebuild it using a triangular or similarly low poly trunk shape, and uv-ing the trunk texture to it. Typically it doesn't matter too much for trunks, as the crowns are more visible for most trees, which is why it is easier to just let it be a billboard. However, some trunks, especially on dead trees, are better 3d.

For crowns, it depends how the texture is setup and the model built, and may be easy or difficult depending on this. 

[z929669]

As DY alludes, trunks are typically less than 1/2 the triangles than crowns and contribute to FPS loss proportionately. It depends on the mod. EVT trunks are relatively high poly compared to most tree mods, ranging between trunks being 1/3 to 2x the triangles of crowns. HLT trunks have more like 1/3 to 1/6 the triangles as crowns.

Decimate or other reduction algorithms (e.g., InstaLOD) normally don't treat trunks well without constraining the modifications in significant ways. This is all resolved by making hybrids with flat trunks using the DynDOLOD tools. Reducing crowns (merging triangles) and re-UV of those are much more forgiving.

If you really do want to tackle trunks, you should focus on the dead trees or those that don't do as well when flattened. You can judge by trunk shape. Straight trunks can be flattened, and bent ones and those with obvious crown branches without foliage hiding them looks more obvious when flattened and should be the focus.

[thismysafespace]

Thank you DoubleYou and z929669! Those were very helpful explanations, and I actually used that guide made by you, z929669, and I found it very helpful. I believe most of my trunks have been flattened already using DynDOLOD tools (that clarification was very helpful). So, to reduce triangles of crowns, you recommend I merge triangles and re-UV? Is this something that your team underwent in creating 3D LODs for various tree mods? Or is it wise to leave the crowns as is?

Thank you, once again, you have both been very helpful

[DoubleYou]

Reduction of the crown may or may not be essential. It depends how high-poly the tree is already, and how the crown is structured, and how sensitive you are to performance. Anything over ~1000 triangles in LOD is generally going to be expensive performance wise. Always aim for as few triangles as possible without causing issues with tree pop in/out. Optimization of the alpha of the crown texture can significantly impact pop in/out as well.

[z929669]

DY actually did the Aspens Ablaze reduction for LOD in Blender I think. My assumption is that he configured Decimate as he liked and re-UV'd, but I'm not sure. It may be possible and simplest to use NifSkope > Optimize functions, but I haven't tested that.

The general idea is to reduce triangles. There are several algorithms in the respective 3D toolsets that could accomplish this for better/worse results. Alternatively, consider manually combining separate leaf/branch polygons into a single shape using a new combined texture and re-UV that.

Either way, the key is to keep the LOD model result as close to the full model result as possible so that transitions are not too obvious in game. This is why an algorithm can be beneficial over manual (tip: constrain overall shape while combining triangles). The latter will often look better, but transitions can be worse without putting in many hours of labor and testing.

Trees can be a lot of work, but they have the advantage of randomness with respect to 3D layout.