If you're new to hard surface or mech texturing, it's easy to get a little lost in the options and functionality of Photoshop actions, or the newer texturing software like the Quixel and Substance suites provide. However, if you do a little texture prep work as you go, it's much easier to get good results.
Keep it tidy, delete unused polys as you go, name your items – or at least groups – and use layers for easy selecting, tweaking and in-program map baking.
Also, be mindful of your high-poly detailing; if it's too densely detailed, your low-poly geometry may not be able to hold your normal map's detail, causing errors – and in some cases, tears in your baked map. As Photoshop can't fix this, you may have to redo parts of your model because of it.
Normals also control smoothing. A smoothing group's function is to make your model appear smoother without adding polys to the mesh. Different modellers have different tools for this, but keep in mind that where one (or more) polygon's smoothing stops, and another starts, a hard edge is created.
Separate these in your UV map if you're baking normals. Even though not every UV shell needs a hard edge, hard edges do need to be separate in your UV map for tangent space normal maps. This is to give room for error-reducing tangent twisting.
If you're creating a wartorn and worn robot, that's full of bullet holes and grunge, consider your model's story when selecting your palette.
For example, did you know that construction equipment is yellow because it's the sole colour in the spectrum that keeps standing out in any environment, even very dark ones? Or that there's a trope for film and TV mechs? Blue, cherry red, muted or earthy tones for the good guys, and blood red, navy, and unmuted, garish colours for the villains.
01. UVs matter
Good texturing bakes come from good UV layouts. Map while your model is still low-poly, and avoid normal artefacts by cutting seams on hard edges when using Smoothing Groups. Remember to create enough space between your UV shells to facilitate edge padding and gutters.
02. UV scale matters
Avoid the novice mistake of disproportionate UVs and thereby textures by applying a checkered UV map with colours, numbers and letters. The default black and white ones usually only show a semblance of stretch or slack, but tend to 'hide' flipped or offscale UVs better.
03. Mind your mesh
When you model, ensure your high and low-poly models are centred with each other to avoid skewed bakes, gradients, black lines, and LOD- issues later. Keep Smoothing Groups, UVs and Cage in mind, and make sure your hard edges are separated in the UV map(s) at bake time.
04. Use ID maps
Make texturing easier by creating an ID map for easy selection and masking, especially when using the Quixel suite. You can bake ID Maps in Max or Maya or Substance, or you can paint one in Photoshop or The GIMP. To avoid masking confusion, just remember that similar colours should never be side by side.
05. Use curvature maps
Generate a curvature map for grungy texture masking, as it renders the bends, hollows and peaks on your model. In the map render, white shows bends or curves – which is where you'll get the most wear, grey is flat, and black denotes dips or dents which is where you'll get dirt and debris.
06. Try a photo as your base texture
Photo-based textures will often read as more 'natural' to the human eye. Try using one that's not too noisy as your detailing base. The wear on a base like this can often have more 'structure' in its random components than an artificial map, and can help your detailing.
07. Mind your painting
Detail for usage, not coolness, even though the concepts are not mutually exclusive. Typically, you'll see wear around joints, on mecha hands and feet, and wear and spillage by fuel-tanks and visible engine(s). If you're a ready-to-renderer, mix the shaders you bought with a curvature (convexity) map generated in freeware map generator, xNormal.
08. Decal conversions
Sometimes you can get great decals as Photoshop brushes only. Save yourself the hassle of manually exporting alpha'd .pngs for applications like ZBrush or Substance Painter, and automate: grab freeware abrMate brush converter, and use it with user Asador's PSBrushesToAlpha script from the Substance forums. Some of the converted files may have softer edges than you want, but that's easily fixed by sharpening and tweaking them in, for example, Photoshop.
09. Layer it on
Layers of subtle build-ups always read better, so take your time when creating your wear and tear. Create scratches, smudges, flakings and dents layer by layer, set to different opacities and modes. This will read better than one big layer of damage.
10. Don't flip UVs
Avoid flipped UVs on your focus areas – even with a FBX export with tangents and binormals checked, you run the risk of odd light and light seams. Tris are hell to UV map, so if at all possible, UV map before you convert and test your model before you add it into your game engine.
This article was originally published in 3D World magazine issue 205.