Feature: Add "Blended" Layer Group for Glass Scenery Objects (X-Plane 12.21+)

[Connor-Russell]

Summary:

Added the "blended" option to non-draped layer groups, for glass scenery objects in X-Plane 12.21+.

Detailed Changes:

xplane_props.py

• Modified the XPlaneLayer property group's layer_group and layer_group_draped properties to get their enum items from callbacks (defined locally in the property group class). This allows for the "blended" layer group to be available only for non-draped layer groups and when the scene's xplane.version property is >= 12.21.
• Cleared the default value for layer_group/layer_group_draped as a string cannot be used with dynamic enums (default is automatically the first item).
• Added version 12.21 to the XPlaneSceneSettings property group's version property, and made 12.21 default.
• Added an update callback to XPlaneSceneSettings.version, this function iterates over every collection, checks for xplane.layer.layer_group property, and if it is an empty string, sets it to LAYER_GROUP_NONE.
  • When the user sets the layer group to blended, then downgrades the X-Plane version to < 12.21, Blender sets the layer_group property to an empty string rather than defaulting to the first value (seemingly a bug in Blender?). The update callback detects this and resets it to LAYER_GROUP_NONE.

xplane_config.py:

• The data model version has been incremented as there are new values for layer_group and xplane.version
  • This may be unnecessary since there are no properties added or removed. I leave this choice to the reviewing author who will know more about this repo than myself.

xplane_constants.py

• Added VERSION_1221 and LAYER_GROUP_BLENDED constants

Testing:

No unit tests were run, however I have verified that .obj exports correctly reflect layer_group changes across version transitions, including fallback behavior when ‘blended’ becomes invalid.

[6639835]

Approved