Probably there is nothing totally new in this article, though, it will be usefull for everybody to remind the main principles that one should keep in mind when working at game graphics, especially if this is graphics outsourcing or freelance. Tips below will help you avoiding typical mistakes concerned with misunderstanding of requirements, badly thought-out pipeline and other issues. You'll also find some rules of proper presentation of your work here.
Once you've got the specs read them attentively, think over all points, ask questions if something is not clear, because even the smallest misunderstanding may lead to bad concecvences. When working at your model check the requirements periodically not to miss some important stage or requirement. Think over the way you are going to create your asset before starting the work not to remake significant volume of work due to the wrong approach
If you are provided with certain pipeline of the assets creation don't ignore it, at least when working on your first models. It's possible that you'll invent a better way to get the same result later, but trying to find a better way when working at first models usually leads to significant volume of fixes and extra work.
When working on models and textures remember that it's hardly possible that you get your work approved from the first time. It's also likely that you or somebody else will have a need to change or fix your model or texture. What I mean is that both model and texture should be suitable for any adjustments. In terms of modeling this means proper geometry, minimal amount of uv seams (and in the least noticable places), absence of uv stretches, uniform scale of details on uvs; in textures - properly structured psd file
Check model twice after you are done. First of all check it for correspondence to client's technical requirements, absence of typical technical mistakes (unwelded vertices, wrong units, objects names, pivots, e.t.c.), check if the textured model looks really good. If your client provided you examples of desired quality see if your model looks the same as the example provided, because even if a very nice work doesn't fit the style it won't be approved.
Learn from mistakes. Make proper conclusions from client's feedbacks and don't make the same mistakes when working on the next models.
Attention! Client doesn't always provide high quality references. To avoid your model looking poor due to the fact that you were unable to make it detailed enough because of the bad references spend some time to look for extra references. Look for more highres blueprints, more detailed images or photos, descriptions of how this object is utlized in real life. If you don't manage - ask your customer to do this.
If your asset contains rotating parts (wheels, doors, etc) - set pivots to the centers of the rotating parts.
Object location : if other is not specified, the asset should be located in the center. If it is symmetrical - it should be absolutely symmetrical related to the axis of symmetry. If there are no reasons to make different mapping for symmetric parts - uvs for symmetric parts should be identical.
Geometry: Check if all vertices are welded, if there are no double edges or polys
Naming: objects should be named as specified in the requirements. In case if this is not specified - create convenient names and follow some logic when naming the meshes. DO NOT name your assets as "building", "house", e.t.c. as it's very easy to get duplicate names this way. You can name your assets the same as the reference provided, for instance you are going to model the King Tiger tank. In this case name the main mesh as kingtiger. Such objects as wheels and turret name as kingtiger_wheel and kingtiger_turret. To mark left and right use “_l” (left) and “_r” (right).
Hierarchy: If nothing is specified - make hierarchy basing on the most probable supposed usage and animation of parts of your mesh. For instance, if it is told to separate the tank into mainbody, wheels, turret and gun it's obvious that wheels and turret will be parented to the mainbody, gun will be parented to the turret. If you don't know what hierarchy is - read corresponding help topics in your modeling package.
Topology: check if meshes with complex shape have correct topology: shape should be represented correctly, there should be no smoothing issues, concerning the characters - be attentive at joints and face.
In general this means that you should make big prominent details by mesh, check if large details are smooth enough and don't model small details or concavities.
In some cases it's not allowed to mirror uvs, but at the moment most of game engines support correct rendering of normal maps at mirrored uvs. Here we suppose that it's allowed to mirror uvs.
When mapping the game models the most important thing is to use uv space thoroughly:
most of details should have the same scale. Though, you should scale up small parts that need much details on texture (for instance, small wheels on the cart), and scale down large details that are hardly visible or have smooth surface (bottom and back polys, thin wires, e.t.c.)/ It's not desirable to scale the uvs more than twice - difference in resolutions wil become too obvious. Moreover, if you can scale something more than twice this means that uvs are packed badly, there is too much free space on uvs and you should consider rearranging the uvs.
remember about the mipmapping - leave at least 4 pixels between your uv parts, if possible - 6-8 pixels. You can easily check the distance between your uv parts making the uv snapshot and viewing it in ACDSEE or Photoshop.
map parts that will have the same or similar color close to each other. The same relates to the parts of the same detail. It's very bad when the top of a small bolt, for instance, is mapped to the one corner of the UV quad and the side - to the opposite corner.
if alpha channel is going to be used for transparency leave at least 10 pixels around the parts that will use alpha channel to avoid issues with mipmapping
locate the uv seams in the least noticeable places
minimize stretching. Don't make any stretching where some details with regular form (bolts, for instance) or text should be present.
mirror the uvs only in such places where it is not going to look too obvious. Fold all cylindric and symmetric details
map to the same uv space those details that use the same texture and don't have nay specific details: wires, pipes, e.t.c.
avoid hidden "wasted space" on uvs. This appears when some detail is located on top of another one on mesh, but is mapped to separate space on uvs, see below:
Note: to avoid issues with texturing it's adviced to scale down a bit the uvs for the part located on top of another one.
don't try to fill the uv quad anyway. If optimized uvs fit the rectangle (half of uv quad) instead of the quad - that's nice too.
when working on uv mapping check the references periodically to see which details are going to be painted on the surface. This is needed not to map the same surfaces to differetn uv space and vice versa - not to map to the same place some parts that need unique texture.
tile long details, such as wires, pipes, e.t.c.
be attentive to the style, check if your work is looking similarly to the samples provided by client
be carefull with small parts and surface details scale. If surface texture is too big it won't look naturally. The same relates to small details, such as bolts and seams - if they are too big the object looks cartoony
dirty object and dirty texture is not the same. Paint dirt thoroughly. Don't think that the more dirt there is in your texture, the better it is.
check if your texture is neither blurry, nor too sharp
use good photos for your textures. I reccomend using textures from http://cgtextures.com/
check if you don't use compressed jpegs: in this case yoru texture will look badly whatever you do. See below how compressed jpeg looks like (look at that "quads" - good quality texture doesn't have such):
if your texture should have plenty of details, but the resolution is low and it's hard for you to paint all the details try painting the more highres texture. When working at more highres texture scale it down and check if the target resolution looks well.
improve your skills. Study shape, light and shadow, materials and textures of the surface, color, perspective; learn traditional painting, photography, sculpture, lighting and anatomy, color theory and design. View portfolios of other artists and companies, analyze what is good and how you can get the same or better results. As the main focus of this article is what you should check, not how to make it looking good, I'd reccomend two books:
- focal_press_3d_game_textures_photoshop.pdf – english book on texturing
- Оуэн Демерс. - Цифровое текстурирование и живопись.pdf – russian book on texturing