Fix wrecks of sinking units ending up below the terrain (#5897)

engine/Core.lua

@@ -103,6 +103,7 @@ end
 --- returns true if a unit category contains this unit
 ---@param category EntityCategory
 ---@param unit Unit | UserUnit | UnitId | Projectile
+---@return boolean
 function EntityCategoryContains(category, unit)
 end
 

lua/ScenarioFramework.lua

@@ -2301,25 +2301,44 @@ function MoveOnMap(unit)
 end
 
 --- Returns the closest point on the map
----@param pos Vector
+---@param position Vector
 ---@return Vector
+---@return boolean
 function GetNearestPlayablePoint(position)
+    local px, _, pz = unpack(position)
     local playableArea = ScenarioInfo.PlayableArea
-    local nearestPoint = {position[1], position[2], position[3]}
 
-    if position[1] < playableArea[1] then
-        nearestPoint[1] = playableArea[1] + 5
-    elseif position[1] > playableArea[3] then
-        nearestPoint[1] = playableArea[3] - 5
+    -- keep track whether the point is actually outside the map
+    local isOutside = false
+
+    if px < playableArea[1] then
+        isOutside = true
+        px = playableArea[1] + 5
+    elseif px > playableArea[3] then
+        isOutside = true
+        px = playableArea[3] - 5
     end
 
-    if position[3] < playableArea[2] then
-        nearestPoint[3] = playableArea[2] + 5
-    elseif position[3] > playableArea[4] then
-        nearestPoint[3] = playableArea[4] - 5
+    if pz < playableArea[2] then
+        isOutside = true
+        pz = playableArea[2] + 5
+    elseif pz > playableArea[4] then
+        isOutside = true
+        pz = playableArea[4] - 5
+    end
+
+    -- if it really is outside the map then we allocate a new vector
+    if isOutside then
+        return {
+            px, 
+            GetTerrainHeight(px, pz),
+            pz
+        }, true
+
     end
 
-    return nearestPoint
+    -- otherwise nothing has changed, so return the existing position
+    return position, false
 end
 
 --- Returns if the unit's army is human

lua/sim/Unit.lua

@@ -1678,6 +1678,7 @@ Unit = ClassUnit(moho.unit_methods, IntelComponent, VeterancyComponent) {
         energy = energy * (bp.Wreckage.EnergyMult or 0)
         local time = (bp.Wreckage.ReclaimTimeMultiplier or 1)
         local pos = self:GetPosition()
+        local wasOutside = false
         local layer = self.Layer
 
         -- Reduce the mass value based on the tech tier
@@ -1706,7 +1707,7 @@ Unit = ClassUnit(moho.unit_methods, IntelComponent, VeterancyComponent) {
 
         -- Create potentially offmap wrecks on-map. Exclude campaign maps that may do weird scripted things.
         if self.Brain.BrainType == 'Human' and (not ScenarioInfo.CampaignMode) then
-            pos = GetNearestPlayablePoint(pos)
+            pos, wasOutside = GetNearestPlayablePoint(pos)
         end
 
         local halfBuilt = self:GetFractionComplete() < 1
@@ -1729,7 +1730,7 @@ Unit = ClassUnit(moho.unit_methods, IntelComponent, VeterancyComponent) {
         -- Attempt to copy our animation pose to the prop. Only works if
         -- the mesh and skeletons are the same, but will not produce an error if not.
         if self.Tractored or (layer ~= 'Air' or (layer == "Air" and halfBuilt)) then
-            TryCopyPose(self, prop, false)
+            TryCopyPose(self, prop, not wasOutside)
         end
 
         -- Create some ambient wreckage smoke

lua/wreckage.lua

@@ -109,7 +109,7 @@ Wreckage = Class(Prop) {
 ---@param energy number
 ---@param time number
 ---@param deathHitBox? table
----@return Prop
+---@return Wreckage
 function CreateWreckage(bp, position, orientation, mass, energy, time, deathHitBox)
     local prop = CreateProp(position, bp.Wreckage.Blueprint)
     prop:SetOrientation(orientation, true)