Methods for Converting Granny2 (.gr2) Animations to .GLB / glTF 2.0 Format:
You can follow three different approaches to eliminate the .gr2 dependency within a BGFX and cross-platform (Android/iOS) architecture:
1. Blender + Python Automation (Most Practical and Stable Method):
Use the open-source GR2 Importer add-on for Blender.
After loading the character skeleton, import the .gr2 animations (e.g., wait.gr2, run.gr2) as additional Actions.
Export the desired .glb file using Blender's built-in glTF/GLB exporter, ensuring you select "Include > Animation" and "Transform > Y-Up."
Tip: You can automate batch conversion for all
files in a folder using the `blender --background --python` command.
2. C++ Command-Line Tool (tinygltf / cgltf + Granny SDK):
Create a C++ project in your Windows development environment and use the Granny SDK (granny2.dll) to read bone, keyframe, and transform data via `FileInfo->Animations`.
Serialize the read binary data into the .glb format in memory using the tinygltf or cgltf library and save the result.
3. Assimp Library:
Using the Assimp C++ API, read the .gr2 file with `ReadFile` and generate .glb output directly via `Assimp::Exporter` using the "glb2" format code.
Important Notes for Mobile (Android/iOS) + BGFX:
Bone Weight Limit: Normalize bone influence (bone weight) per vertex to a maximum of 4 bones.
Matrix Array Limit: Limit the total number of bones in the model to 64 or 128 to avoid exceeding mobile GPU shader uniform limits. Quaternion Normalization: Ensure that Rotation Quaternion (XYZW) values are normalized during transformation to prevent limb stretching in BGFX.
