Avoid errors in posn-at-point for large images

* src/keyboard.c (Fposn_at_point): If pos-visible-in-window-p
returns a 6-member list for a partially visible glyph, pass the
sum of Y and RTOP to posn-at-x-y, since that's where the visible
portion of that glyph begins on display.  (Bug#24804)  (Bug#21832)
(Bug#23809)

1 files changed, 8 insertions, 0 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index bb411e77823..65938a5eb56 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -10790,11 +10790,19 @@ The `posn-' functions access elements of such lists.  */)
     {
       Lisp_Object x = XCAR (tem);
       Lisp_Object y = XCAR (XCDR (tem));
+      Lisp_Object aux_info = XCDR (XCDR (tem));
+      int y_coord = XINT (y);
 
       /* Point invisible due to hscrolling?  X can be -1 when a
          newline in a R2L line overflows into the left fringe.  */
       if (XINT (x) < -1)
         return Qnil;
+      if (!NILP (aux_info) && y_coord < 0)
+        {
+          int rtop = XINT (XCAR (aux_info));
+
+          y = make_number (y_coord + rtop);
+        }
       tem = Fposn_at_x_y (x, y, window, Qnil);
     }