Refactor uses of scroll_margin to a function

Its effective range needs to be clamped between 0 and (window height /
4), so it's better to have this constraint in a single place.

* src/window.c (window_scroll_margin): New function.
(window_scroll_pixel_based, window_scroll_line_based):
(Frecenter, Fmove_to_window_line):
* src/xdisp.c (try_scrolling, try_cursor_movement):
(redisplay_window, try_window, try_window_id): Use it.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/window.h b/src/window.h
index 061cf244943..acb8a5cabfa 100644
--- a/src/window.h
+++ b/src/window.h
@@ -1120,6 +1120,8 @@ extern bool compare_window_configurations (Lisp_Object, Lisp_Object, bool);
 extern void mark_window_cursors_off (struct window *);
 extern int window_internal_height (struct window *);
 extern int window_body_width (struct window *w, bool);
+enum margin_unit { MARGIN_IN_LINES, MARGIN_IN_PIXELS };
+extern int window_scroll_margin (struct window *, enum margin_unit);
 extern void temp_output_buffer_show (Lisp_Object);
 extern void replace_buffer_in_windows (Lisp_Object);
 extern void replace_buffer_in_windows_safely (Lisp_Object);