Loading Screen Mod speeds up custom asset loading and saves RAM by sharing textures, materials and meshes. This guide describes how asset creators can make the most of this feature.


Sharing means reusing. The game saves a hash (a unique identifier) with each texture, material and mesh (resources for short). Before loading a resource from disk, LSM checks if its hash is a known one. If yes then the resource is already in memory and there is no need to load and decode it again. Obviously this saves time and memory. The Unity game engine supports shared resources.


Identical resource data is required. File names do not matter but file contents must be exactly the same. For materials, in particular, this means that the contained textures must be the same and also other material properties (for example colors) must be exactly the same.


Sharing works across almost all boundaries. It works between different asset types, between assets in an asset pack, and between different workshop submissions. Sharing works automatically for identical resources; no special actions are required.

As an example, let's assume Jim published a building asset back in 2016. In 2019, Jane gets permission to reuse a texture from Jim's building in her road asset. Because it is exactly the same texture, sharing will work.

Of course there are some limitations:

• Sharing does not work for LOD textures. Reloading the texture from disk is not necessary but an in-memory duplicate is created. Curiously, perhaps, sharing DOES work for LOD materials. This is explained below.
  
  
• For textures and materials, the game stores mains and LODs separately, so sharing is not possible across the main-LOD boundary. However, there is no such limitation for meshes.
  
  
• There is no sharing between vanilla prefabs and custom assets. However, sharing across the vanilla-custom boundary does work for LOD materials.

Asset authors should pay special attention to LOD materials because of how the game is designed.

To speed up rendering, Cities Skylines crams all LOD textures into a large texture called atlas. There is a separate texture atlas for Buildings, Props, Vehicles, and Nets. The maximum size of an atlas is 4096 x 4096. If space runs out, Unity scales down LOD textures until they fit in.

Because of game design, LOD texture sharing is not possible. However, LOD material sharing works and prevents storing the same texture many times in the limited-size atlas. This for sure seems counterintuitive because materials consists of textures but that is how the game works.

For an example, please view the images below. You can see the Net texture atlas in three different scenarios:

1. Vanilla Net prefabs only.[thale5.github.io]
   No custom assets. The largest vanilla LOD textures are 128 x 128. Atlas size is 2048 x 1024.
   
   
2. Vanilla Net prefabs + one workshop item subscribed.[thale5.github.io]
   Sharing is enabled in Loading Screen Mod. Atlas size is 2048 x 2048.
   
   
3. Vanilla Net prefabs + one workshop item subscribed (the same as above).[thale5.github.io]
   Loading Screen Mod is disabled. Atlas size is 4096 x 4096 (maxed out).

Because of the down-scaling applied in scenario 3, all Net LODs may look blurry.

To avoid scenario 3, keep LOD texture sizes to a minimum and reuse materials as much as possible.


I have added an option in Loading Screen Mod to check assets for errors and warnings.

An error is reported if any LOD texture size is not a power of two (16, 32, 64, and so on).
Use power-of-two texture sizes only! Otherwise, sooner or later, you are going to see black textures in-game, thanks to how the above-mentioned LOD texture atlas works.

An error is also reported if an asset has been unsuccessfully edited with a binary file editor in an attempt to avoid duplicate prefab messages. More about duplicates below.

Warnings are issued for:

• LOD texture is large (512 x 512 or larger).
  
• LOD mesh is large (600 triangles or 1000 vertices).

Asset names matter because the game identifies and finds assets by name. It is not possible to have two assets with the same name in-game!

It is important to realize that asset file names do NOT matter at all. Asset name is determined by the Asset Name field in the Save Asset dialog.

The common pitfalls are:

• Duplicate prefab name errors: this happens when several assets in the same asset pack have the same name. Typically the same trailer name, sub-building name or net pillar or elevation name is used several times in the pack.
  
  
• Asset Name (in the Save Asset dialog) is modified when the asset is updated for the workshop. Because the game finds assets by name, the game considers the updated asset a different one. Users who have placed the asset see it disappear because the old asset name no longer exists.

Many users consider duplicate prefab messages annoying. Authors who create asset packs can easily avoid the messages by making sure that different assets have different names. Loading Screen Mod does NOT issue the message if the identically named assets have identical content (the unmodded game still reports them).

The situation where the identically named assets have different content is harmful and is reported (Consider: two different assets, only one of them can be loaded, which one? The mod or game cannot tell so it must be reported).


The 'Optimize thumbnails' option in Loading Screen Mod speeds up custom asset loading and saves RAM. This feature is not related to resource sharing but is accomplished by storing UI textures more space-efficiently without quality loss. Quite surprisingly, the feature makes a big difference. It is comparable to resource sharing.

The only prerequisite for this feature is that game-default thumbnail and tooltip texture sizes must be used. Some asset authors have used non-standard UI texture sizes. Just stick to the default sizes, which are a bit odd: 109 x 100 for thumbs and 492 x 147 for tooltips.


To support the 'Check assets for errors' feature in Loading Screen Mod, some short Guides are available:

Invalid LOD texture size
Asset naming conclict
Large LOD texture
Large LOD mesh

My old Guide is still current:

Workshop assets must not use private assets