how do obj files work once loaded.

Question

Can anyone provide me with a high level over view of how obj or other 3d formats work. I'm trying to learn 3D programming for games but all the tutorials i've found so far only show how to create and manipulate primitives such as a sphere etc. I'm using java but i also know C# and C++ i've just never done games programming or any 3D modelling.

Say for example if i have an obj file of a road and i load it. If any parts of the model is animated can i trigger that from inside the code or does it automatically happen?

The second thing, if i had another model which was a car, can i import that car and add it to the road in the first obj file? or would they need to be included in one obj file?

The last thing would be, if the car wheels were animated. Is there a way to stop them once i know the model is not moving in the scene, and then of course start them spinning again later?

I know it might be best to buy a book but i don't know if its something i want to get into yet, i'm just testing to see if i'll stick with it and asfter i decide i can then buy a 3d graphics book or similar. thanks

Answer 1

Say for example....inside the code or does it automatically happen?...The second thing... The last thing would be...spinning again later?

The answer for the three questions depends on what software you use for the 3D "world". If you use a framework, like XNA, then you will have many helper functions for animations and the like. If you create the world with OpenGL, or the like, then you will be writing the code for the animations (and just about everything else).

File formats for 3d assets vary wildly in what and how they store information. Some can contain entire scenes while others store only a single mesh. I would suggest you have a look at the AutoDesk FBX site. Although the format is not technically documented, it seems reasonable place for a start as the format is generally stored in clear text and can contain variety of objects including animations. The SDK, tools and viewers are available for free...well free with registration:) Then grab Blender, it is an excellent open source 3D editor that can handle most formats...could be helpful in learning what the different formats can do.

At the end of the day everything is just a triangle...with normals...a little color...maybe a texture...some shading...