Below is a list of common issues found with StemCell v2 models. Please use this as a reference for issues to avoid, and thus have a smoother submission experience.
Surface Normals
Surface normals on geometry sometimes are corrupted, independent of any material attributes. Be sure to check your verification renders carefully, and that your objects surface normals are not corrupted, flipped or otherwise have any issues. Below you can see the face normals on the wing when they are corrupted versus when they are fixed.
Corrupt
Fixed
Visible Backfaces
Visible backfaces on models are not allowed for StemCell, as this causes major visual issues in the Real Time formats. Real Time models with visible backfaces need to be fixed by adding thickness to the model. Below is an example of a t-shirt where the model does not have a thickness so you can see through the geometry in the back. While there is geometry there, it is single sided, and its normals are facing the other direction, so we end up seeing the transparent backfaces.
Overlapping UVs
UV overlap is a very common issue. It is important to know when overlapping UVs are acceptable and not. Please refer to our best practices for UV mapping.
Out of Bounds UVs
There are situations like using tileable textures where you might need to scale up UVs and have them outside of the 0-1 UV space.
However, there are also occasions where having UVs outside of the 0-1 UV space is not practical, as seen in the images below. Be sure in those cases, your UVs are within the 0-1 space, and have a reasonable amount of padding away from the outer edges.
Refraction/Transmission Workflow
Another common issue is using opacity maps for refractive type materials. Be sure opacity is only used for cutout type materials, like plants or haircards.
All other types of transparent materials should be created using refraction/transmission maps. For more information, see links below.
Invalid Normal Map Values
Oftentimes, normal map values are produced incorrectly. Some common issues include overly blue normal maps, or maps with too wide of a color range (rainbow-like appearance). This is often caused by adding incorrect gamma to the maps, or using RGB curves. Normal maps are very specific in their value range and anything outside of those values often results in either visual or software errors.
Incorrect Normal Values
Correct Values
As a general rule RGB 128, 128, 255 is the neutral value for a normal map. You can find helpful information about normal maps here.
Scene Elements
In some cases, models are being submitted with animation, rigs, or other modifiers not supported by StemCell. While StemCells pipeline does strip these elements out for the most part, it is best to remove any of those unsupported elements manually to avoid issues.Your scene submission should ideally only include the model, its materials, and textures.
Exchange Formats
Some submissions include multiple exchange formats and 3d files submitted in a single archive, but the pipeline only supports 3ds Max or Blender submissions. Having exchange formats in your archive might also trigger false positives in our malicious file scanners and cause errors and submission failures. The StemCell pipeline produces the most widely used exchange formats for you automatically, so it is best to leave these out of your submissions.
