4.1 Exporters

Exporters are plugins to 3D modelling tools which write meshes and skeletal animation to file formats which OGRE can use for realtime rendering. The files the exporters write end in .mesh and .skeleton respectively.

Each exporter has to be written specifically for the modeller in question, although they all use a common set of facilities provided by the classes MeshSerializer and SkeletonSerializer. They also normally require you to own the modelling tool.

All the exporters here can be built from the source code, or you can download precompiled versions from the OGRE web site.

A Note About Modelling / Animation For OGRE

• You must have no more than 4 weighted bone assignments per vertex. If you have more, OGRE will eliminate the lowest weighted assignments and renormalise the other weights. This limit is imposed by hardware blending limitations.
• All vertices must be assigned to at least one bone - assign static vertices to the root bone.
• At the very least each bone must have a keyframe at the beginning and end of the animation.

Milkshape3D

Milkshape3D is a popular low-polygon editor, especially popular in the modding community because of it's low price and the fact that it supports many game file formats. Installation instructions are included with the exporter itself. The Milkshape exporter supports exporting of meshes and animations. An important tip: Make sure you are not in 'animation' mode when you do this, otherwise Milkshape gets confused as to what the 'reference' position of the mesh is. Just make sure the 'Anim' button in the bottom-right is NOT depressed.

You then get a dialog box with several options:

Export Mesh

Obvious really - if checked this exports the geometry data (vertex positions, normals & texture coordinates) to a .mesh file.

Export Skeleton & Animation

If checked, the bones of the model and animation data is exported to a .skeleton file.

Split Keyframe Sequence Into Multiple Animations

You can check this to split the single timeline in Milkshape into multiple separate animations (this option has no effect if you are not exporting the skeleton). This is necessary because Milkshape doesn't have a concept of multiple separate animations, you just have to model them all in a single timeline and then use this feature to split them up. If you check this box you must supply a text file which tells OGRE how to split the animation up. This text file is very simple: each line is a single animation, and must contain comma-separated values indicating the start frame, end frame and name of the animation, e.g.:

1,30,Walk 31,45,Run 46,75,Die ...etc

Frame Rate

The Milkshape timeline is in frames, but OGRE likes to deal with animations in terms of seconds for simplicity. This value allows the exporter to do the conversion. Note there's nothing to stop you animating the mesh at a different frame rate in OGRE at runtime by scaling the amount you change the animation by each time, but this bakes a 'default animation speed' into the animation for simplicity.

3D Studio Max R4/5

Other exporters

• Wings3D
• Blender
• Maya
• Lightwave