[COMMIT] Don't return a Charbpos before visible region, start_with_line_at_pixpos()

Thank you Julian!

APPROVE COMMIT

NOTE: This patch has been committed.

# HG changeset patch
# User Aidan Kehoe <[email protected]>
# Date 1390264036 0
# Node ID cfc6a8c144f16b2598435cfb0aa8a2a48204c947
# Parent  7277cf461612be80403c68d3368a5b3329210e3d
Don't return a Charbpos before visible region, start_with_line_at_pixpos()

src/ChangeLog addition:

2014-01-21  Aidan Kehoe  <[email protected]>

	* redisplay.c (start_with_line_at_pixpos):
	Apply Julian Bradfield's change of
	[email protected] , never returning a
	Charbpos before the visible region. Thank you Julian!

diff -r 7277cf461612 -r cfc6a8c144f1 src/ChangeLog
--- a/src/ChangeLog	Mon Jan 20 18:13:15 2014 +0000
+++ b/src/ChangeLog	Tue Jan 21 00:27:16 2014 +0000
@@ -1,3 +1,10 @@
+2014-01-21  Aidan Kehoe  <[email protected]>
+
+	* redisplay.c (start_with_line_at_pixpos):
+	Apply Julian Bradfield's change of
+	[email protected] , never returning a
+	Charbpos before the visible region. Thank you Julian!
+
 2014-01-20  Aidan Kehoe  <[email protected]>
 
 	* fileio.c (Fcopy_file, Finsert_file_contents_internal):
diff -r 7277cf461612 -r cfc6a8c144f1 src/redisplay.c
--- a/src/redisplay.c	Mon Jan 20 18:13:15 2014 +0000
+++ b/src/redisplay.c	Tue Jan 21 00:27:16 2014 +0000
@@ -8287,12 +8287,15 @@
       if (pixheight < 0)
 	{
 	  w->line_cache_validation_override--;
-	  if (-pixheight > point_line_height)
-	    /* We can't make the target line cover pixpos, so put it
-	       above pixpos.  That way it will at least be visible. */
-	    return prev_pos;
-	  else
-	    return cur_pos;
+          /* I see no reason why cur_pos can't be before BEGV
+             here, so check for it. It's not clear to me whether
+             prev_pos could be before BEGV, so check that as well. */
+          if (-pixheight > point_line_height)
+            /* We can't make the target line cover pixpos, so put it
+               above pixpos.  That way it will at least be visible. */
+            return (prev_pos <= BUF_BEGV (b)) ? BUF_BEGV (b) : prev_pos;
+          else
+            return (cur_pos <= BUF_BEGV (b)) ? BUF_BEGV (b) : cur_pos;
 	}
 
       cur_elt--;


-- 
‘Liston operated so fast that he once accidentally amputated an assistant’s
fingers along with a patient’s leg, […] The patient and the assistant both
died of sepsis, and a spectator reportedly died of shock, resulting in the
only known procedure with a 300% mortality.’ (Atul Gawande, NEJM, 2012)

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