SelectionBox Overlays (SelectionBoxManager)

SelectionBoxManager is the game's system for drawing world-space wireframe/filled boxes (prefab editor volumes, land claim previews, sleeper volumes). Mods can use it for their own overlays: SelectionBoxManager.Instance.CreateCategory(...) then category.AddBox(name, pos, size).

Gotcha: categories start INACTIVE — activate before AddBox

CreateCategory calls SetVisible(false) on the new category before returning, and SelectionCategory.SetVisible is gameObject.SetActive on the category's GameObject. AddBox parents each new SelectionBox GameObject under the category transform.

Consequence: a box added while its category is hidden sits under an inactive parent, so Unity never runs the box's Awake(). Awake() is what creates the mesh child and assigns m_MeshRenderer / materials. Calling ShowThroughWalls(bool) (and anything else touching m_MeshRenderer.materials) on such a box throws NullReferenceException inside SelectionBox.

Fix / rule: call category.SetVisible(true) before AddBox (or before the first method that touches the box's renderer), not after configuring the boxes.

var cat = SelectionBoxManager.Instance.CreateCategory("MyCat", col, col, col, false, "", 0);
cat.SetVisible(true);                       // MUST come first
var box = cat.AddBox("box1", pos, size);    // Awake() runs here now
box.SetVisible(true);
box.ShowThroughWalls(true);                 // safe

Symptom in the log: NullReferenceException with top frame SelectionBox.ShowThroughWalls (System.Boolean _bShow).

Other notes

• Categories/boxes live on scene GameObjects: a world reload creates a fresh SelectionBoxManager.Instance, invalidating cached SelectionCategory refs. Compare the cached manager instance and re-create categories when it changes.
• ShowThroughWalls sets the _ZTest shader property (8 = Always, 4 = LEqual) on the frame and face materials.
• Reuse boxes via category.TryGetBox(name, out box) + box.SetPositionAndSize(...); AddBox with an existing name removes and recreates the box.
• Decompile game classes with ilspycmd -t <TypeName> "<GameDir>\7DaysToDie_Data\Managed\Assembly-CSharp.dll" (installed as a dotnet global tool).