Add code to detect case where the first visible line in a window is a

partially-visible continued line and is subsequently deleted.
Previously this caused the redisplay to go into an uninterruptible
infinite loop.

This is yet another change in the series of revisions 1.25 and 1.30.
Revision 1.30 only partially fixed this bug.  This revision introduces
a new fix that should be more robust.

diff --git a/v7/src/edwin/bufwiu.scm b/v7/src/edwin/bufwiu.scm
index 08caa6b0940b675f81b25a87149fc505c285a56a..d76db27aa20eaac385002b1cdde56e6191648740 100644 (file)
--- a/v7/src/edwin/bufwiu.scm
+++ b/v7/src/edwin/bufwiu.scm
@@ -1,6 +1,6 @@
 ;;; -*-Scheme-*-
 ;;;
-;;; $Id: bufwiu.scm,v 1.32 2000/02/28 22:50:37 cph Exp $
+;;; $Id: bufwiu.scm,v 1.33 2000/04/10 02:27:41 cph Exp $
 ;;;
 ;;; Copyright (c) 1986, 1989-2000 Massachusetts Institute of Technology
 ;;;
@@ -45,17 +45,9 @@
          (if start
              (begin
                ;; If this change affects START-MARK, invalidate it
-               ;; and request a display update.  Don't invalidate
-               ;; START-MARK unless the changes require it.
+               ;; and request a display update.
                (if (and (%window-start-line-mark window)
-                        (let ((wlstart (%window-start-line-index window))
-                              (wstart (%window-start-index window)))
-                          (and (if (and (fix:= wlstart wstart)
-                                        (fix:= (%window-start-partial window)
-                                               0))
-                                   (fix:< start wstart)
-                                   (fix:<= start wstart))
-                               (fix:<= wlstart end))))
+                        (%start-clobbered? window start end))
                    (begin
                      (clear-window-start! window)
                      (window-needs-redisplay! window)))
@@ -66,6 +58,27 @@
                    (begin
                      (%set-window-point-moved?! window 'SINCE-START-SET)
                      (window-needs-redisplay! window)))))))))
+
+(define-integrable (%start-clobbered? window start end)
+  (let ((wlstart (%window-start-line-index window))
+       (wstart (%window-start-index window))
+       (partial (%window-start-partial window)))
+    (or (and (%window-current-start-delta window)
+            ;; If the delta between START-LINE and START has changed
+            ;; since the last redisplay, then the window start has
+            ;; been clobbered.  For example, if the first line was
+            ;; only partially visible, and is then entirely deleted,
+            ;; WLSTART and WSTART will be equal -- which would
+            ;; normally indicate that the window start is OK.
+            (not (and (fix:= (%window-current-start-delta window)
+                             (fix:- wstart wlstart))
+                      (fix:= (%window-current-start-partial window)
+                             partial))))
+       (and (if (and (fix:= wlstart wstart)
+                     (fix:= 0 partial))
+                (fix:< start wstart)
+                (fix:<= start wstart))
+            (fix:<= wlstart end)))))
 \f
 ;;;; Clip