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====== FBX Importing ======

Importing FBX files in Unity with the correct scale, rotation, and axis is fraught.
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===== Scaling =====

FBX is in cm by default, but can support other units. Other unit scales are achieved in FBX by by setting ''GlobalSettings->Properties70->UnitScaleFactor'' property in the fbx. For example, a 1 meter cube in 'meters' should be stored in an fbx file like:
<code yaml>
GlobalSettings:
  Properties70:
    UnitScaleFactor = (100.0)   # The 'unit' is 100 * 1cm 
CubeObject:
  Lcl Scaling = (1,1,1)
</code>

This file will show up in Unity's importer as '1m (File)'. [[https://uninomicon.com/_detail/unity_uhvnfc5tw5.png|image]]

++++ Instructions for Blender |

In order to achieve the above scaling (scale of 1 on objects, UnitScaleFactor=100), in the export settings set one of the following for ''Transform->Apply Scaling'':
  * FBX Units Scale
  * FBX All

++++

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===== Rotation =====

In the FBX file format, global axis alignment is stored in the GlobalSettings:
  * UpAxis: 0,0,1 (+Z)
  * FrontAxis: 0,1,0 (+Y)
  * CoordAxis: -1,0,0 (-X)
  * OriginalUpAxis: ??? <sup>[//[[:wiki:tag:research-needed|research needed]]//]</sup>

Unity uses these properties to determine the coordinate system for the file. On import, the asset will be rotated to convert it from the file-coordinate system, to the Unity coordinate system. __As of 2020.1, when "Bake Axis Conversion" is checked, these rotations will be baked into the meshes, rather than applied in the transforms.__

For **Blender** it's important to note the difference between the terms "Front" and "Forward". Front refers to the direction a model //faces//. In Blender this is -Y, in Unity this is +Z. Forward refers to the direction you would walk when looking at a model from the front. In Blender this is +Y and in Unity this is +Z. ((At some point pre 2015, Blender [[https://developer.blender.org/T43935|incorrectly had these terms swapped]] and exported all models with a 180 flip because of it.))

++++ Instructions for Blender ~2.92 |
Unity's 'Bake Axis Conversion' checkbox is [[https://forum.unity.com/threads/bake-axis-conversion-import-setting.899072/#post-6975023|buggy]], however it seems to be the most reliable way to get the correct rotation from objects exported from Blender.

In Blender 2.92, the export behavior changed slightly, so we can simply:
  * Axis must be set as -Y Forward ((because of the previous bug, this is 180 degrees opposite to the correct axis. Blend files naturally have a +Y Forward aka. -Y Front orientation for axis)), and Z Up. ((Blender coordinates))
  * "Use Space Transform" **must** be off. ((This feature was, [[https://forum.unity.com/threads/bake-axis-conversion-defaults-to-models-looking-backwards.910298/|interestingly]], built to help export to Unity properly. However, this actually adds a root rotation to the file, which can confuse other tools))
  * In Unity, select: "Bake Axis Conversion"
{{ :blender_6pdtp5vutg.png }}
{{ :unity_4iszlno6j5.png }}
++++
++++ Instructions for Blender ~2.90 |
Note! This path is buggy. Blender does not seem to apply transforms to objects deeper than 2 parents in the hierarchy. Recommended not to use this path.

* Select "!Experimental! Apply Transforms". 
  * Axis must be set as -Z Forward, and Y Up.
  * In Unity, "Bake Axis Conversion" must be **off**.
{{ :blender_5lcugkdlz1.png }}
{{ :unity_4iszlno6j5.png }}

//Note: If your object does not support Apply Transforms, you should either [[https://www.immersivelimit.com/tutorials/blender-to-unity-export-correct-scale-rotation|counter-rotate]] the object, or upgrade to Blender >2.92.//
++++

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