fix(api/buffer): fix handling of viewport of non-current buffer

A lot of functions in move.c only worked for curwin, alternatively
took a `wp` arg but still only work if that happens to be curwin.

Refactor those that are needed for update_topline(wp) to work
for any window.

fixes #27723
fixes #27720

1 files changed, 8 insertions, 5 deletions

diff --git a/test/functional/lua/ffi_spec.lua b/test/functional/lua/ffi_spec.lua
index c9e8e9d4ca..4229e4af9b 100644
--- a/test/functional/lua/ffi_spec.lua
+++ b/test/functional/lua/ffi_spec.lua
@@ -13,15 +13,19 @@ describe('ffi.cdef', function()
 
     eq(
       12,
-      exec_lua [[
+      exec_lua [=[
       local ffi = require('ffi')
 
-      ffi.cdef('int curwin_col_off(void);')
+      ffi.cdef [[
+        typedef struct window_S win_T;
+        int win_col_off(win_T *wp);
+        extern win_T *curwin;
+      ]]
 
       vim.cmd('set number numberwidth=4 signcolumn=yes:4')
 
-      return ffi.C.curwin_col_off()
-    ]]
+      return ffi.C.win_col_off(ffi.C.curwin)
+    ]=]
     )
 
     eq(
@@ -30,7 +34,6 @@ describe('ffi.cdef', function()
       local ffi = require('ffi')
 
       ffi.cdef[[
-        typedef struct window_S win_T;
         typedef struct {} stl_hlrec_t;
         typedef struct {} StlClickRecord;
         typedef struct {} statuscol_T;