3D modelling guidelines

CHILI publisher cannot be used to design a 3D model from scratch.
A 3D model has to be created in a 3D application such as 3D Studio Max for example.

In CHILI Publisher models are rendered in real time.
They are rendered using the GPU. This means we have to follow some guidelines to make sure these models are suited for real time rendering.

Number of triangles

A 3D model is made out of one or more meshes (objects). A mesh is a collection of triangles:

More triangles means more detail, but it also means the collada file will be bigger.
CHILI can easily render 3D models made out of 100 000 polygons, but it will take a long time to download and parse the collada file.
We advise to keep the triangle count below 25 000 triangles.

Single sided geometry

By default collada surfaces are considered single sided. Any double sided material in your 3D design software will be converted to a single sided material.
This is common practice in 3D as it can speed up the rendering of solid objects.
However for thin objects like a sheet of paper it sometimes makes sense to have 2 sides.
In those case the geometry must be duplicated and the face normal need to be inverted.

Normals

A normal vector defines which way a triangle is facing.

CHILI Publisher only supports single sided materials.
Because of this it is very important the normals are facing in the right direction.

Bad face normals can be recognized by black triangles or holes in your model.
If the normals are inverted you will see the inside of your 3D model instead of the outside.

Bad normal cannot be fixed in CHILI Publisher. This issue has to be resolved in the 3D application you are using.

For performance, use smooth normals. Faceted faces are counter intuatively less performant.

Z-fighting

As with other 3D rendering engines, CHILI Publisher uses a z-buffer to determine visual priorities.
If 2 faces coincide a flickering effect might occur. This visual glitch is called z-fighting.

It can be avoided by not using coinciding faces.
If you need to model two layers, like the label of a bottle, make sure the top layer has an offset.

To make sure there are no visual glitches, test your model in CHILI Publisher’s 3D viewer.

UV coordinates

A document is mapped onto a 3D model by using a UV map.
A UV map is a collection of 3D coordinates with their corresponding 2D coordinates (document coordinates).

These 2D coordinates are normalized. So they are values between 0 and 1.
Most 3D applications will allow UV coordinates below 0 or above 1.
However, to make sure your model is rendered correctly in CHILI Publisher, all UV coordinates must be between 0 and 1.

Simply creating a cylinder and exporting it to collada will likely result in coordinates outside the 0-1 range, so please be aware of this restriction.

Because Publisher cannot do anything with meshes without UV coordinates, these meshes won't be rendered.

Materials

Any materials defined in your 3D model will be ignored.
All materials need to be re-created in CHILI Publisher.

CHILI Publisher only supports Phong style effects.

To distinguish the printable part from the other parts, the printable part should use a unique material.
So in your 3D modelling software, make sure you have one material that you only use for the printable area.
It is advised to export your CHILI document to an image and use that while UV mapping the printable area of your 3D model.

Different types of collada files

There are different types of collada files:

• The “regular” collada files have the extension .dae.
  They are based on XML.

• There are also collada archives.
  These archives have the extension .zdae.
  They are a zipped package containing a .dae file, textures and a description file. 

CHILI Publisher only supports .dae files.
If you have a .zdae file, rename it to .zip, and extract the .dae file from it.