The Example Project

This project is designed to test the Blender export facilities and the stand-alone file conversion utilities needed to move 3D objects from Blender, where you build them, to the Auran Jet game engine, where you use them.

Last updated: 12/01/2001

The Initial Objective

The project is intentionally simple so we can check any part of it by hand without getting lost in a vast sea of 3D data. It consists of just two cubes. One is covered with a grid texture projected using the Blender's Cube option. The other is split into two separate pieces: a single flat face supporting a plain concrete texture, and the remaining five sides using a simple green material and no texture. Here's the original objects displayed in Blender with direct and fill lighting.

Out first objective is to create one Jet object displaying the grid pattern on the "face" of the grid cube, and another Jet object displaying the green material and concrete pattern on the small cube. Don't worry about the rest of the faces on the large cube yet, Jet requires that we break it into separate faces to texture each face individually, but that is easy to do.

The object of this initial exercise is to create an ExportGridCube.im Jet Indexed Mesh file for the grid cube, and an ExportSmallCube.im Jet Indexed Mesh file for the small cube.

The final result, running in a simple Jet application, looks like this (note that this picture uses undirected ambient lighting and a somewhat different camera angle, so shadows, highlights and the background are all a bit different):

The conversion routines project the grid texture directly through the large cube. If viewed from the back, you would see a reversed image of the front texture, just as you would in Blender. The top, bottom, and sides are pixels extruded back through the cube, and may change as the angle of view to the object changes.

The Process

The process used to move these objects from Blender to the Jet engine include the following steps:

• Create or find the textures you will need. I created 128BitGrid.tga using the GIMP image manipulation program, and I found concrete064.tga on a free list on the Internet. I used Targa (*.tga) files because they support alpha data (when needed), and look good when resized. Note: Jet does not support compressed *.tga files, so you will not be able to use this feature. Make sure that each dimension is a power of 2, or Jet will be unable to load them into Open GL components.
  
  
• Build the 3D objects in Blender, TestCube.blend in this case.
  
  
• Use the GenericExport.py Python script from within Blender to export the structure of the 3D objects to the BlenderExport.txt export file (see Export Script for details).
  
  
• Manually create the BlenderExportSplitCtrl.txt file to control which 3D objects go into each individual resource file. In this case, the large cube object goes into one file while the face object (which gets the concrete texture) and the rest of the small cube that was split away from the face go into another file. BlenderExportSplitCtrl.txt is a very simple file, and should not change unless you add new objects or change the structure of existing objects.
  
  
• Run the export file splitter to create the two object-specific export files: ExportGridCube.txt and ExportSmallCube.txt. If you only have a single objet in your Blender file, you can skip these two steps.
  
  
• Manually create the BlenderExportTextures.txt file to describe the two textures used, and to link them to their parent surfaces. This step will be obsolete once Blender can export texture information directly through its Python interface. In the meantime, the file should not change much unless you change your texture names or properties a lot
  
  
• Run the export file converter against each of the object-specific export files and the texture file to create two Jet Indexed Mesh files: ExportGridCube.im and ExportSmallCube.im
  
  
• Create a Jet application to load and display these resource files. I modified the original IndexedMesh example which simply orbits the camera around the loaded meshes (which automatically go directly into the same locations they had in the Blender environment) using simple ambient light.

Despite the simplicity of this example, I have used this process to export fairly complex objects. The monorail I'm playing with has about 7500 polygons in 45 separate components made up from 15 different 3D Blender objects. There are also about 15 different pieces in the initial track objects which use, in some cases, over a thousand additional polygons for each track section. The process to export, split, and convert all of this is surprisingly fast and easy. When we fix the workarounds, it will be even easier. To see the models mentioned here, click here to see the real project.

Next Steps

Next steps include the following

• Get tiled textures working in Jet.
• Get bump maps and multiple-texture configurations working in Jet.
• Work with the Blender community to export Blender texture information through the Python interface.
• Look at exporting bones, influences, and other aspects of articulated models.
• Look for an algorithm to create varying levels of detail (LOD) from standard mesh objects.