Animated Creature via COLLADA

This tutorial shows how to get an animated creature from Blender to OpenMW using the COLLADA format. It does not cover using Blender itself, as there are many better resources for that. The focus is solely on the animation pipeline and its specific requirements. Most of them are related to how the model, rig, and animations are set up in Blender.

Note

This tutorial builds upon the Static Model via COLLADA tutorial. All fundamentals of exporting static objects apply to animated ones as well.

Requirements

To use the Blender to OpenMW pipeline via COLLADA, you will need the following.

• OpenMW 0.48 or later
• Blender 2.83 or later. Latest confirmed, working version is Blender 3.0
• OpenMW COLLADA Exporter
• An animated model you would like to export. In our case the flamboyant Land Racer!

The Land Racer

The creature, and its revelant files, are available from the Example Suite repository. This should be useful for further study of how to set things up in case this tutorial is not clear on any particular thing.

• data/meshes/land_racer.dae – exported model
• data/meshes/land_racer.txt – animation textkeys
• data/textures/land_racer.dds – diffuse texture
• data/textures/land_racer_n.dds - normal map
• source_assets/land_racer.blend – source file configured as this tutorial specifies

Model

The model needs to be a child of the rig and have an Armature modifier asigned. Bone weights are limited to a maximum of 4 bones per vertex. The model needs to have default location, rotation, and scale.

Collision Shape

Collision is set up with an empty named Collision or collision with a single child mesh. OpenMW will use the bounding box of this mesh for physics collision shape so a simple, cuboid mesh is enough. If no collision shape is defined, the bounding box of the animated model will be used instead.

Armature / Rig

Note

Only a single rig object should be included in the exported file. Exporting multiple rigs is not reliably supported and can lead to errors.

Root

The rig needs to be structured in a specific way. There should be a single top bone in the rig’s hierarchy, the root bone named Bip01. The name is required so OpenMW recognizes and uses it for root movement. For this same reason, the bone should be by default aligned with the world. The root bone needs to have its Deform flag enabled.

Deform Bones

Below the root bone, the bones are divided into two branches. One branch contains the deform bones which get included in the final exported file. These are otherwise not animated directly but inherit motion from other bones via constraints. They have their Deform flag enabled. For creatures, the deform bones can be named as you desire and don’t need to follow the naming convention used for NPC and player models.

Control Bones

The other branch holds control and helper bones that enable comfortable animation in Blender, but are neither required nor included in the exported file. They have their Deform flag disabled. How these bones are structured is a big separate topic on its own that this tutorial does not cover, but you can study the provided source file.

Animations

A creature in OpenMW is expected to have a set of animations to display its various actions. These animations are recognized and used by their name.

Animation name	Possible variations	Purpose
attack1	attack2, attack3	The creature performs an attack
death1	death2 - death5	The creature dies while upright
hit1	hit2 - hit5	The creature is hit in combat
idle	idle2 - idle9	Flavour animations when the creature does nothing in particular
knockout	/	When creature’s fatigue goes below 0 and it staggers to the ground
deathknockout	/	The creature dies while knocked out
knockdown	/	When the creatures receives a heavy hit in combat or lands from a considerable height
deathknockdown	/	The creature dies while knocked down
runforward	/	Moving forward fast
walkforward	/	Moving forward at regular speed

Animating in Blender is done at 30 fps. Specific to how OpenMW works, each exported animation needs to take a unique range on the timeline. To achieve this, actions are placed as strips in the NLA editor with an obligatory one frame gap between them.

NLA strips affect the exported result based on their scale, name, frame range, repetition, or any other factor affecting the end animation result. It’s What you see is what you get principle.

Root movement is required for animations such as walkforward and runforward and is likely to work for other animations if needed. Root movement works only when the root bone is named Bip01.

Textkeys

The exported COLLADA file requires a corresponding textkeys file for OpenMW to properly read the animations. Textkeys is a .txt file containing animation definitions and events. At a minimum it needs to include at least animation start and stop values in a format as shown in this example.

idle: start 0.033333
idle: stop 2.033333
walkforward: start 2.066667
walkforward: stop 3.666667
runforward: start 3.7
runforward: stop 4.433333
attack1: start 4.466667
attack1: stop 5.433333
...

The textkeys file is placed in the same folder as the model and matches the model’s name.

• meshes/land_racer.dae
• meshes/land_racer.txt

While it’s possible to write it by hand, OpenMW’s Collada Exporter offers a convenient option to export a textkeys file based on Blender’s timeline markers (not to be confused with pose markers which are contained per action). What you need to do is create properly named timeline markers for each animation and enable the Export Textkeys option in the exporter.

In the example of walkforward the timeline markers should be named walkforward: start and walkforward: stop.

Exporter Settings

For animated models, use the following exporter settings. Before export, select all objects you wish to include in the exported file and have the Selected Objects option enabled. Without this, the exporter could fail.

Getting the Model In-game

Once the Land Racer is exported, both of its .dae and .txt files need to be placed in the correct folder where OpenMW will read it. Afterwards in OpenMW-CS, it should be visible in the Assets->Meshes table and can be assigned to the Model/Animation field of a creature.