From 5aeb6d91e98acac434b3fcefe76f25d067fb7d0b Mon Sep 17 00:00:00 2001
From: lL1l1 <82986251+lL1l1@users.noreply.github.com>
Date: Sat, 18 Jan 2025 18:49:08 -0800
Subject: [PATCH 1/3] Fix `QuatFromXZDirection` for negative dx inputs

---
 lua/utilities.lua | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/lua/utilities.lua b/lua/utilities.lua
index 0b33e22d8e..539fffe778 100644
--- a/lua/utilities.lua
+++ b/lua/utilities.lua
@@ -487,13 +487,32 @@ end
 ---@param dz number
 ---@return Quaternion
 function QuatFromXZDirection(dx, dz)
-    -- ang = atan2(dx, dz) -- `dz` is adjacent
-    -- {0, sin(ang/2), 0, cos(ang/2)}
+    -- division by zero case
+    if dx == 0 and dz == 0 then
+        return UnsafeQuaternion(0, 0, 0, 1)
+    end
+
+    -- q = (0, sin(ang/2), 0, cos(ang/2))       -- definition of our y-axis rotation quaternion we want to get for angle `ang`
+
+    -- sin(ang/2) = +/-sqrt((1-cos(ang))/2)     -- half angle formula for sin. +/- is sign of sin(ang/2)
+    --            = +/-sqrt( 0.5 - cos(ang)/2 )
+    --            = +/-sqrt( 0.5 - a/2h )       -- cos(ang) = adjacent/hypotenuse
+    -- similar is repeated for cos(ang/2)
+
     local hypot = MathSqrt(dx*dx + dz*dz)
-    -- use the half-angle formulas
     local halfCosA = dz / (2 * hypot)
     local sinHalfA = MathSqrt(0.5 - halfCosA)
     local cosHalfA = MathSqrt(0.5 + halfCosA)
+
+    -- Resolve the +/- part of our result:
+    -- sign of sin(ang/2) is + for ang in (0, 2pi)
+    -- sign of cos(ang/2) is + for ang in (0, pi) and - for ang in (pi, 2pi)
+    -- ang in (pi, 2pi) is when dx is negative, so negate cosHalfA in that case
+
+    if dx < 0 then
+        return UnsafeQuaternion(0, sinHalfA, 0, -cosHalfA)
+    end
+
     return UnsafeQuaternion(0, sinHalfA, 0, cosHalfA)
 end
 

From df6cf7d7a5e1c8cc05e8b6c233930cb16fe686ef Mon Sep 17 00:00:00 2001
From: lL1l1 <82986251+lL1l1@users.noreply.github.com>
Date: Sat, 18 Jan 2025 18:49:41 -0800
Subject: [PATCH 2/3] Use GetPosXYZ in Unit RotateTowards

---
 lua/sim/Unit.lua | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lua/sim/Unit.lua b/lua/sim/Unit.lua
index 94503d4e40..19d0e04f0a 100644
--- a/lua/sim/Unit.lua
+++ b/lua/sim/Unit.lua
@@ -2262,8 +2262,8 @@ Unit = ClassUnit(moho.unit_methods, IntelComponent, VeterancyComponent, DebugUni
     ---@param self Unit
     ---@param tpos Vector
     RotateTowards = function(self, tpos)
-        local pos = self:GetPosition()
-        local dx, dz = tpos[1] - pos[1], tpos[3] - pos[3]
+        local pX, _, pZ = self:GetPositionXYZ()
+        local dx, dz = tpos[1] - pX, tpos[3] - pZ
         self:SetOrientation(utilities.QuatFromXZDirection(dx, dz), true)
     end,
 

From e475b21beb0ae093a23315eb65eda7f61156363c Mon Sep 17 00:00:00 2001
From: lL1l1 <82986251+lL1l1@users.noreply.github.com>
Date: Sat, 18 Jan 2025 19:06:47 -0800
Subject: [PATCH 3/3] Create fix.6630.md

---
 changelog/snippets/fix.6630.md | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog/snippets/fix.6630.md

diff --git a/changelog/snippets/fix.6630.md b/changelog/snippets/fix.6630.md
new file mode 100644
index 0000000000..00384cf6c6
--- /dev/null
+++ b/changelog/snippets/fix.6630.md
@@ -0,0 +1 @@
+- (#6630) Fix ACUs spawned on the right side of the map not facing towards the middle of the map.