Serve viewport dimensions through view_width and view_height

These values are useful for calculating terminal positions.

vis-lua.c

@@ -1833,6 +1833,14 @@ static const struct luaL_Reg registers_funcs[] = {
  * Viewport currently being displayed.
  * @tfield Range viewport
  */
+/***
+ * Viewport height, accounting for window decorations.
+ * @tfield int view_height
+ */
+/***
+ * Viewport width, accounting for window decorations.
+ * @tfield int view_width
+ */
 /***
  * The window width.
  * @tfield int width
@@ -1872,6 +1880,16 @@ static int window_index(lua_State *L) {
 			return 1;
 		}
 
+		if (strcmp(key, "view_width") == 0) {
+			lua_pushunsigned(L, view_width_get(win->view));
+			return 1;
+		}
+
+		if (strcmp(key, "view_height") == 0) {
+			lua_pushunsigned(L, view_height_get(win->view));
+			return 1;
+		}
+
 		if (strcmp(key, "width") == 0) {
 			lua_pushunsigned(L, vis_window_width_get(win));
 			return 1;