Add menu docs

Author: ChristopherHX

src/SUMMARY.md

@@ -25,4 +25,5 @@ Edition). The launcher supports Linux and OS X.
     - [NDK Shims](./extra/advanced/ndk_shims/index.md)
     - [Modding Api](./extra/advanced/modding-api/index.md)
     - [Game Window Api](./extra/advanced/game-window-api/index.md)
+    - [Menu Api](./extra/advanced/menu-api/index.md)
 - [External Links](./external_links/index.md)

src/extra/advanced/index.md

@@ -4,4 +4,5 @@
 - [JNI](./jni/index.md)
 - [NDK Shims](./ndk_shims/index.md)
 - [Modding Api](./modding-api/index.md)
-- [Game Window Api](./game-window-api/index.md)
+- [Game Window Api](./game-window-api/index.md)
+- [Menu Api](./menu-api/index.md)

src/extra/advanced/menu-api/index.md

@@ -0,0 +1,118 @@
+# Menu API Reference
+
+Integrate custom menus below the mods menu item and create custom windows with interactive controls using the `libmcpelauncher_menu.so` library.
+
+## `MenuEntryABI` Structure
+
+Defines a single menu entry with potential subentries.
+
+```cpp
+struct MenuEntryABI {
+    const char* name;                    // Name shown in the UI
+    void* user;                          // Custom user data passed to callbacks
+    bool (*selected)(void* user);       // Selection callback
+    void (*click)(void* user);          // Click callback
+    size_t length;                      // Number of subentries
+    MenuEntryABI* subentries;           // Pointer to array of subentries
+};
+```
+
+---
+
+## `void mcpelauncher_addmenu(size_t length, MenuEntryABI* entries);`
+
+Adds a group of menu entries to the launcher.
+
+- `length`: Number of items in `entries`
+- `entries`: Pointer to array of `MenuEntryABI`
+
+---
+
+## `control` Structure
+
+Represents a UI control embedded in a window.
+
+```cpp
+struct control {
+    int type; // Enum-like control type
+    union {
+        struct {
+            const char* label;
+            void* user;
+            void (*onClick)(void* user);
+        } button;
+
+        struct {
+            const char* label;
+            int min;
+            int def;
+            int max;
+            void* user;
+            void (*onChange)(void* user, int value);
+        } sliderint;
+
+        struct {
+            const char* label;
+            float min;
+            float def;
+            float max;
+            void* user;
+            void (*onChange)(void* user, float value);
+        } sliderfloat;
+
+        struct {
+            const char* label;
+            int size; // 0 = normal, 1 = small title
+        } text;
+
+        struct {
+            const char* label;
+            const char* def;
+            const char* placeholder;
+            void* user;
+            void (*onChange)(void* user, const char* value);
+        } textinput;
+    } data;
+};
+```
+
+### Control Types
+
+Set `type` to match the control structure being used:
+- `0`: Button
+- `1`: Slider (integer)
+- `2`: Slider (float)
+- `3`: Static text
+- `4`: Text input
+
+---
+
+## `void mcpelauncher_show_window(...)`
+
+Displays a window populated with interactive controls.
+
+```cpp
+void mcpelauncher_show_window(
+    const char* title,
+    int isModal,
+    void* user,
+    void (*onClose)(void* user),
+    int count,
+    control* controls
+);
+```
+
+### Parameters
+
+- `title`: Title displayed on the window
+- `isModal`: Modal flag (non-zero blocks other inputs)
+- `user`: Custom user data passed to callbacks
+- `onClose`: Callback called when window closes
+- `count`: Number of controls
+- `controls`: Pointer to array of `control` structs
+
+---
+
+## `void mcpelauncher_close_window(const char* title);`
+
+Closes the window with the specified title.