kernel: Add get_active_window_struct

fox32os.def

@@ -29,6 +29,7 @@ fill_window:               jmp [0x00000C28]
 get_window_overlay_number: jmp [0x00000C2C]
 start_dragging_window:     jmp [0x00000C30]
 new_messagebox:            jmp [0x00000C34]
+get_active_window_struct:  jmp [0x00000C38]
 
 ; VFS jump table
 open:                      jmp [0x00000D10]

kernel/main.asm

@@ -45,6 +45,7 @@ jump_table:
     data.32 get_window_overlay_number
     data.32 start_dragging_window
     data.32 new_messagebox
+    data.32 get_active_window_struct
 
     ; VFS jump table
     org.pad 0x00000510

kernel/window/window.asm

@@ -646,6 +646,16 @@ window_list_offset_to_struct:
     mov r0, [r0]
     ret
 
+; get a pointer to the active window struct
+; inputs:
+; none
+; outputs:
+; r0: pointer to current window struct
+get_active_window_struct:
+    movz.8 r0, [active_window_offset]
+    call window_list_offset_to_struct
+    ret
+
 window_title_bar_patterns:
     ; 1x16 tile
     data.32 0x00000000