Added the ability to import scenes as AnimationLibrary
* Completes implementation of https://github.com/godotengine/godot-proposals/issues/4296
* Helps if you want to export animations to a separate file (say a GLTF) to avoid re-importing/exporting them every time the model changes.
* Helps if you simply want to have animations using a dummy model, which can be shared across multiple models.
Creates a secondary scene importer used only for animations.
**NOTE**: A new flag for scene importer: EditorSceneFormatImporter.IMPORT_DISCARD_MESHES_AND_MATERIALS has been added, to hint importers that they should skip meshes and animations (and hence make importing faster). It is not implemented in any importer yet, this should be done in a separate PR.
With this PR it's possible to add a collision during the Mesh import, directly in editor.
To generate the shape is possible to chose between the following options:
- Decompose Convex: The Mesh is decomposed in one or many Convex Shapes (Using the VHACD library).
- Simple Convex: Is generated a convex shape that enclose the entire mesh.
- Trimesh: Generate a trimesh shape using the Mesh faces.
- Box: Add a primitive box shape, where you can tweak the `size`, `position`, `rotation`.
- Sphere: Add a primitive sphere shape, where you can tweak the `radius`, `position`, `rotation`.
- Cylinder: Add a primitive cylinder shape, where you can tweak the `height`, `radius`, `position`, `rotation`.
- Capsule: Add a primitive capsule shape, where you can tweak the `height`, `radius`, `position`, `rotation`.
It's also possible to chose the generated body, so you can create:
- Rigid Body
- Static Body
- Area
* Added option for importers to show an Advanced settings dialog
* Created advanced settings dialog for Scene Importer
* Cleaned up importers (remove many old/unused options)
* Added the ability to customize every node, material, mesh and animation individually
* Saving to animations and meshes to files is now a manual process, making it more predictable
* Added the ability for materials to be replaced by external files (or to be made external, up to you).
* When doubleclicking an impoted scene in the filesystem dock, it automatically shows the import settings instead of asking to open it.
WARNING: Lightmap UV unwrap is not working, it needs to be re-made.
