frame: add frame:GetEffectiveAlpha()

Own alpha times every ancestor's alpha -- the product WoW composites at
render time. Vanilla has only GetAlpha (a frame's own alpha); this walks
self -> parent -> ... via the engine's own GetAlpha/GetParent, so it
reflects the engine exactly, including 8-bit alpha quantization
(SetAlpha(0.5) -> 127/255). Frame-scoped, matching GetAlpha's registry.

Verified in-game: matches an equivalent Lua GetAlpha/GetParent walk, and
a two-level 0.5/0.5 chain returns (127/255)^2 = 0.248043 exactly.

Author: brues-code

README.md

@@ -35,7 +35,7 @@ Full per-function reference: **[docs/API.md](docs/API.md)**.
 | [Expansion](docs/API.md#expansion) | `ClassicExpansionAtLeast`, `ClassicExpansionAtMost`, `GetClassicExpansionLevel` |
 | [Faction](docs/API.md#faction) | `C_Reputation.GetFactionDataByIndex`, `C_Reputation.GetFactionStandings`, `C_Reputation.GetLastStandingChange`, `C_Reputation.GetWatchedFactionData`, `C_Reputation.SetWatchedFactionByID`, `GetFactionIDByIndex`, `GetFactionInfoByID`, `GetFactionParentID` |
 | [Focus](docs/API.md#focus) | `ClearFocus`, `FocusUnit` |
-| [Frame](docs/API.md#frame) | `region:SetPoint("point")` (one-arg form), `region:SetSize`, `region:GetSize`, `region:IsMouseOver`, `region:GetRect`, `region:IsDragging`, `frame:SetShown`, `frame:SetResizeBounds`, `frame:HookScript`, `frame:IsEventRegistered` |
+| [Frame](docs/API.md#frame) | `region:SetPoint("point")` (one-arg form), `region:SetSize`, `region:GetSize`, `region:IsMouseOver`, `region:GetRect`, `region:IsDragging`, `frame:SetShown`, `frame:SetResizeBounds`, `frame:HookScript`, `frame:IsEventRegistered`, `frame:GetEffectiveAlpha` |
 | [FriendList](docs/API.md#friendlist) | `C_FriendList.IsWhoQueryPending`, `C_FriendList.SendWhoQueryByName` |
 | [GameObject](docs/API.md#gameobject) | `C_GameObjectInfo.GetGameObjectInfoByID`, `C_GameObjectInfo.RequestLoadGameObjectByID`, `ClosestGameObjectPosition` |
 | [Gossip](docs/API.md#gossip) | `C_GossipInfo.CloseGossip`, `C_GossipInfo.GetActiveQuests`, `C_GossipInfo.GetAvailableQuests`, `C_GossipInfo.GetNumActiveQuests`, `C_GossipInfo.GetNumAvailableQuests`, `C_GossipInfo.GetNumOptions`, `C_GossipInfo.GetOptions`, `C_GossipInfo.GetText`, `C_GossipInfo.SelectActiveQuest`, `C_GossipInfo.SelectAvailableQuest`, `C_GossipInfo.SelectOption`, `C_GossipInfo.SelectOptionByIndex` |

docs/API.md

@@ -162,6 +162,7 @@ build instructions.
   - [`frame:SetResizeBounds(minWidth, minHeight [, maxWidth, maxHeight])`](#framesetresizeboundsminwidth-minheight--maxwidth-maxheight)
   - [`frame:HookScript(scriptType, handler)`](#framehookscriptscripttype-handler)
   - [`frame:IsEventRegistered(event)`](#frameiseventregisteredevent)
+  - [`frame:GetEffectiveAlpha()`](#framegeteffectivealpha)
 
 - [FriendList](#friendlist)
   - [`C_FriendList.SendWhoQueryByName(name)`](#c_friendlistsendwhoquerybynamename)
@@ -3691,6 +3692,22 @@ f:IsEventRegistered("PLAYER_LOGIN")   -- true
 f:IsEventRegistered("PLAYER_LOGOUT")  -- false
 ```
 
+### `frame:GetEffectiveAlpha()`
+
+Returns the frame's **effective** alpha — its own `GetAlpha()` multiplied
+by every ancestor's, i.e. the opacity WoW actually composites at render
+time (fading `UIParent` fades all of its children). Vanilla exposes only
+`GetAlpha` (a frame's own alpha); this walks `self → parent → …` via the
+engine's own `GetAlpha`/`GetParent`, so it sees exactly what the engine
+does — including the 8-bit quantization of alpha (`SetAlpha(0.5)` stores
+`127/255 ≈ 0.498`, and effective alpha is the product of those).
+
+```lua
+UIParent:GetEffectiveAlpha()   -- 1
+-- with UIParent at 0.5 and Minimap's own alpha 1:
+Minimap:GetEffectiveAlpha()    -- ~0.498 (0.5 truncates to 127/255)
+```
+
 ## FriendList
 
 ### `C_FriendList.SendWhoQueryByName(name)`

src/Offsets.h

@@ -1346,6 +1346,10 @@ enum Offsets {
     FUN_SCRIPT_FRAME_SETMAXRESIZE = 0x007762A0,
     FUN_SCRIPT_FRAME_GETSCRIPT = 0x00774780,
     FUN_SCRIPT_FRAME_SETSCRIPT = 0x007748D0,
+    // Frame GetAlpha (own alpha, 0..1) + Region GetParent — walked by
+    // Frame::Modern's GetEffectiveAlpha up the parent chain.
+    FUN_SCRIPT_FRAME_GETALPHA = 0x00774DC0,
+    FUN_SCRIPT_REGION_GETPARENT = 0x007A1460,
     FUN_SCRIPT_TEXTURE_SHOW = 0x0079B770,
     FUN_SCRIPT_TEXTURE_HIDE = 0x0079B830,
     FUN_SCRIPT_FONTSTRING_SHOW = 0x0079CDB0,

src/frame/Modern.cpp

@@ -40,6 +40,9 @@
 //   - `frame:HookScript(scriptType, handler)` — absent in vanilla
 //     entirely. Chains after any existing handler and invokes `handler`
 //     with modern positional args (see the implementation comment).
+//   - `frame:GetEffectiveAlpha()` — own alpha × the parent chain's, the
+//     product WoW composites at render time. Frame-scoped (matches
+//     GetAlpha); walks the parents via the engine's own getters.
 //
 // Implementation style: each new method delegates to the ENGINE's own
 // Script_* implementations by reshaping the Lua stack and calling them
@@ -214,6 +217,33 @@ int __fastcall Script_SetShown(void *L) {
     return 0;
 }
 
+// ---- GetEffectiveAlpha (Frame) ---------------------------------------------
+
+// `frame:GetEffectiveAlpha()` — the frame's own alpha times every
+// ancestor's alpha, i.e. the product WoW composites at render time (fading
+// UIParent fades all children). Vanilla exposes only GetAlpha (own alpha);
+// we walk self → parent → … via the engine's own GetAlpha (Frame) and
+// GetParent (Region), so no field offsets or scale math are re-derived. The
+// iteration cap is a defensive guard against a pathological chain (WoW frame
+// trees are shallow; the loop normally ends when GetParent returns nil at
+// the top of the tree).
+int __fastcall Script_GetEffectiveAlpha(void *L) {
+    Game::Lua::SetTop(L, 1); // (obj) = self
+    double eff = 1.0;
+    for (int guard = 0; guard < 128; ++guard) {
+        CallScript(Offsets::FUN_SCRIPT_FRAME_GETALPHA, L); // (obj, alpha)
+        eff *= Game::Lua::ToNumber(L, 2);
+        Game::Lua::SetTop(L, 1);                             // (obj)
+        CallScript(Offsets::FUN_SCRIPT_REGION_GETPARENT, L); // (obj, parent|nil)
+        if (Game::Lua::Type(L, 2) == Game::Lua::TYPE_NIL)
+            break;
+        Game::Lua::Remove(L, 1); // drop obj → (parent) becomes index 1
+    }
+    Game::Lua::SetTop(L, 0);
+    Game::Lua::PushNumber(L, eff);
+    return 1;
+}
+
 // ---- SetResizeBounds (Frame) -----------------------------------------------
 
 // `frame:SetResizeBounds(minWidth, minHeight [, maxWidth, maxHeight])` —
@@ -404,6 +434,7 @@ const Game::Lua::FrameMethodEntry g_frameMethods[] = {
     {"SetResizeBounds", &Script_SetResizeBounds},
     {"HookScript", &Script_HookScript},
     {"IsEventRegistered", &Script_IsEventRegistered},
+    {"GetEffectiveAlpha", &Script_GetEffectiveAlpha},
 };
 
 const Game::Lua::FrameMethodEntry g_textureMethods[] = {