Trim... What? Tile... Who?
First things first, what is a tileable texture?
A tileable texture, also known as a seamless texture, is a texture that can be repeated across a mesh without the borders being noticeable to the person looking at it.
As you can see, I can expand or make it smaller as much as I want without it giving away a clear visual indication of a seam between the repetitions.
This is the same example with a non-tielable texture. Much worse, right?
The more you tile it or repeat it, the more apparent the repetition is. Tileable textures work best when mixed with other tileables via vertex painting or height blends to mask those landmarks that make us go: "Aha! There's the pattern!"
Trim textures, also known as a trimsheets, are textures composed of multiple mini textures, tileable or not, something similar to an atlas or tileset (for those of you who remember working on RPG Maker :D).
What's it useful for?
Reducing the time for texturing of a general area and keeping it consistent. Imagine a temple from the Uncharted franchise or God Of War 2018: there needs to be cohesion and connectivity between all the ornaments and motives throughout a building.
Trim textures are specially useful for PBR (Physically Based Rendering), where you don't care if there are overlaps in the UVs of the final model. Repurposing trim textures is a super fast and relaible way to create texture variation and use it in different ways. For example, the same trim can be used for texturing props or for texturing the whole building.
Pics by Polygon Academy (Tim Simpson) (https://www.polygon-academy.com/, https://twitter.com/polygon_academy & https://www.youtube.com/channel/UCGXr6E_g91ue1rfhA9j4TLA)
This texturing method relies a lot on how you unwrap your mesh and how the trim texture is laid out. you can either start planning the textures first before modelling, or the other way around. We'll need to plan it either way, because both affect the next step.
Let's reuse the textures from the exterior of the Tomb Chaser pyramid to make a simple column that could be reused in the interiors. This is the current Trim Texture used to beautify the whole exterior. Yes, it's all a single material!
So let's make a column divided in sections and you'll see how fast you can change the design once we have our geometry there, just by switchting the UVs around.
This is going to be our column. As you can see, it has many differentiated sections that are going to be assigned to different sections of the texture. Let's cut those sections in the UVs, right where they change from section from section.
See how cylinders are unwrapped in linear fashion? This is key for taking advantage of our texture space and patterns throughout the model.
After this we can begin modifying the UVs to fit into the preexisting "sections" of the Trim Texture.
And once that's done, creating variations of this is really, really easy. We just need to move the UV Shells around to other Trim sections!
We can create variations with the same geometry and the same texture, just by modifying the UVs of the mesh. We can also make a variation of the texture and it'll automatically apply to the already UV'd mesh with different colours/patterns as long as you leave the pattern separation consistent
I hope you learned something new today! See you around :)