TIP #438 (Ensure Line Metrics are Up-to-Date) accepted by vote

6 files changed, 504 insertions, 38 deletions

diff --git a/doc/text.n b/doc/text.n
index 976503b..ac7803c 100644
--- a/doc/text.n
+++ b/doc/text.n
@@ -917,6 +917,83 @@ affected.
 .PP
 See below for the \fIpathName \fBpeer\fR widget command that controls the
 creation of peer widgets.
+.SH "ASYNCHRONOUS UPDATE OF LINE HEIGHTS"
+.PP
+In order to maintain a responsive user-experience, the text widget calculates
+lines metrics (line heights in pixels) asynchronously. Because of this, some
+commands of the text widget may return wrong results if the asynchronous
+calculations are not finished at the time of calling. This applies to
+\fIpathName \fBcount -ypixels\fR and \fIpathName \fByview\fR.
+.PP
+Again for performance reasons, it would not be appropriate to let these
+commands always wait for the end of the update calculation each time they are
+called. In most use cases of these commands a more or less inaccurate result
+does not really matter compared to execution speed.
+.PP
+In case accurate result is needed (and if the text widget is managed by a
+geometry manager), one can resort to \fIpathName \fBsync\fR and \fIpathName
+\fBpendingsync\fR to control the synchronization of the view of text widgets.
+.PP
+The \fB<<WidgetViewSync>>\fR virtual event fires when the line heights of the
+text widget becomes obsolete (due to some editing command or configuration
+change), and again when the internal data of the text widget are back in sync
+with the widget view. The detail field (%d substitution) is either true (when
+the widget is in sync) or false (when it is not).
+.PP
+\fIpathName \fBsync\fR, \fIpathName \fBpendingsync\fR and
+\fB<<WidgetViewSync>>\fR apply to each text widget independently of its peers.
+.PP
+Examples of use:
+.CS
+## Example 1:
+# immediately complete line metrics at any cost (GUI unresponsive)
+$w sync
+$w yview moveto $fraction
+
+## Example 2:
+# synchronously wait for up-to-date line metrics (GUI responsive)
+# before executing the scheduled command, but don't block execution flow
+$w sync -command [list $w yview moveto $fraction]
+
+## Example 3:
+# init
+set yud($w) 0
+proc updateaction w {
+\&set ::yud($w) 1
+\&# any other update action here...
+}
+# runtime, synchronously wait for up-to-date line metrics (GUI responsive)
+$w sync -command [list updateaction $w]
+vwait yud($w)
+$w yview moveto $fraction
+
+## Example 4:
+# init
+set todo($w) {}
+proc updateaction w {
+\&foreach cmd $::todo($w) {uplevel #0 $cmd}
+\&set todo($w) {}
+}
+# runtime
+lappend todo($w) [list $w yview moveto $fraction]
+$w sync -command [list updateaction $w]
+
+## Example 5:
+# init
+set todo($w) {}
+bind $w <<WidgetViewSync>> {
+\&if {%d} {
+\&\&foreach cmd $todo(%W) {eval $cmd}
+\&\&set todo(%W) {}
+\&}
+}
+# runtime
+if {![$w pendingsync]} {
+\&$w yview moveto $fraction
+} else {
+\&lappend todo($w) [list $w yview moveto $fraction]
+}
+.CE
 .SH "WIDGET COMMAND"
 .PP
 The \fBtext\fR command creates a new Tcl command whose name is the same as the
@@ -981,7 +1058,9 @@ if the text widget is managed by a geometry manager), then all subsequent
 options ensure that any possible out of date information is recalculated.
 This currently only has any effect for the \fB\-ypixels\fR count (which, if
 \fB\-update\fR is not given, will use the text widget's current cached value
-for each line). The count options are interpreted as follows:
+for each line). This \fB\-update\fR option is obsoleted by \fIpathName
+\fBsync\fR, \fIpathName \fBpendingsync\fR and \fB<<WidgetViewSync>>\fR.  The
+count options are interpreted as follows:
 .RS
 .IP \fB\-chars\fR
 count all characters, whether elided or not. Do not count embedded windows or
@@ -1344,13 +1423,16 @@ Returns a list of peers of this widget (this does not include the widget
 itself). The order within this list is undefined.
 .RE
 .TP
-\fIpathName \fBreplace \fIindex1 index2 chars\fR ?\fItagList chars tagList ...\fR?
-.
-Replaces the range of characters between \fIindex1\fR and \fIindex2\fR with
-the given characters and tags. See the section on \fIpathName \fBinsert\fR for
-an explanation of the handling of the \fItagList...\fR arguments, and the
-section on \fIpathName \fBdelete\fR for an explanation of the handling of the
-indices. If \fIindex2\fR corresponds to an index earlier in the text than
+\fIpathName \fBpendingsync\fR
+Returns 1 if the line heights calculations are not up-to-date, 0 otherwise.
+.TP
+\fIpathName \fBreplace\fR \fIindex1 index2 chars\fR ?\fItagList chars tagList ...\fR?
+Replaces the range of characters between \fIindex1\fR and \fIindex2\fR
+with the given characters and tags.  See the section on \fIpathName
+\fBinsert\fR for an explanation of the handling of the \fItagList...\fR
+arguments, and the section on \fIpathName
+\fBdelete\fR for an explanation of the handling of the indices.  If
+\fIindex2\fR corresponds to an index earlier in the text than
 \fIindex1\fR, an error will be generated.
 .RS
 .PP
@@ -1523,6 +1605,23 @@ the view just enough to make \fIindex\fR visible at the edge of the window.
 If \fIindex\fR is far out of view, then the command centers \fIindex\fR in the
 window.
 .TP
+\fIpathName \fBsync\fR ?\fB-command \fIcommand\fR?
+Controls the synchronization of the view of the text widget.
+.RS
+.TP
+\fIpathName \fBsync\fR
+Immediately brings the line metrics up-to-date by forcing computation of any
+outdated line heights. The command returns immediately if there is no such
+outdated line heights, otherwise it returns only at the end of the computation.
+The command returns an empty string.
+.TP
+\fIpathName \fBsync -command \fIcommand\fR
+Schedules \fIcommand\fR to be executed (by the event loop) exactly once as soon
+as all line heights are up-to-date. If there are no pending line metrics
+calculations, the scheduling is immediate. The command returns the empty
+string. \fBbgerror\fR is called on \fIcommand\fR failure.
+.RE
+.TP
 \fIpathName \fBtag \fIoption \fR?\fIarg arg ...\fR?
 .
 This command is used to manipulate tags. The exact behavior of the command
diff --git a/generic/tkText.c b/generic/tkText.c
index a713e7e..3079417 100644
--- a/generic/tkText.c
+++ b/generic/tkText.c
@@ -402,6 +402,7 @@ static Tcl_Obj *	TextGetText(const TkText *textPtr,
 			    const TkTextIndex *index2, int visibleOnly);
 static void		GenerateModifiedEvent(TkText *textPtr);
 static void		UpdateDirtyFlag(TkSharedText *sharedPtr);
+static void		RunAfterSyncCmd(ClientData clientData);
 static void		TextPushUndoAction(TkText *textPtr,
 			    Tcl_Obj *undoString, int insert,
 			    const TkTextIndex *index1Ptr,
@@ -702,15 +703,16 @@ TextWidgetObjCmd(
     static const char *const optionStrings[] = {
 	"bbox", "cget", "compare", "configure", "count", "debug", "delete",
 	"dlineinfo", "dump", "edit", "get", "image", "index", "insert",
-	"mark", "peer", "replace", "scan", "search", "see", "tag", "window",
-	"xview", "yview", NULL
+	"mark", "peer", "pendingsync", "replace", "scan", "search",
+	"see", "sync", "tag", "window", "xview", "yview", NULL
     };
     enum options {
 	TEXT_BBOX, TEXT_CGET, TEXT_COMPARE, TEXT_CONFIGURE, TEXT_COUNT,
 	TEXT_DEBUG, TEXT_DELETE, TEXT_DLINEINFO, TEXT_DUMP, TEXT_EDIT,
 	TEXT_GET, TEXT_IMAGE, TEXT_INDEX, TEXT_INSERT, TEXT_MARK,
-	TEXT_PEER, TEXT_REPLACE, TEXT_SCAN, TEXT_SEARCH, TEXT_SEE,
-	TEXT_TAG, TEXT_WINDOW, TEXT_XVIEW, TEXT_YVIEW
+	TEXT_PEER, TEXT_PENDINGSYNC, TEXT_REPLACE, TEXT_SCAN,
+	TEXT_SEARCH, TEXT_SEE, TEXT_SYNC, TEXT_TAG, TEXT_WINDOW,
+	TEXT_XVIEW, TEXT_YVIEW
     };
 
     if (objc < 2) {
@@ -1392,6 +1394,16 @@ TextWidgetObjCmd(
     case TEXT_PEER:
 	result = TextPeerCmd(textPtr, interp, objc, objv);
 	break;
+    case TEXT_PENDINGSYNC: {
+        if (objc != 2) {
+            Tcl_WrongNumArgs(interp, 2, objv, NULL);
+            result = TCL_ERROR;
+            goto done;
+        }
+        Tcl_SetObjResult(interp,
+                Tcl_NewBooleanObj(TkTextPendingsync(textPtr)));
+        break;
+    }
     case TEXT_REPLACE: {
 	const TkTextIndex *indexFromPtr, *indexToPtr;
 
@@ -1506,6 +1518,39 @@ TextWidgetObjCmd(
     case TEXT_SEE:
 	result = TkTextSeeCmd(textPtr, interp, objc, objv);
 	break;
+    case TEXT_SYNC: {
+	if (objc == 4) {
+	    Tcl_Obj *cmd = objv[3];
+	    const char *option = Tcl_GetString(objv[2]);
+	    if (strncmp(option, "-command", objv[2]->length)) {
+		Tcl_AppendResult(interp, "wrong option \"", option, "\": should be \"-command\"", NULL);
+		result = TCL_ERROR;
+		goto done;
+	    }
+	    Tcl_IncrRefCount(cmd);
+	    if (TkTextPendingsync(textPtr)) {
+		if (textPtr->afterSyncCmd) {
+		    Tcl_DecrRefCount(textPtr->afterSyncCmd);
+		}
+		textPtr->afterSyncCmd = cmd;
+	    } else {
+		textPtr->afterSyncCmd = cmd;
+                Tcl_DoWhenIdle(RunAfterSyncCmd, (ClientData) textPtr);
+	    }
+	    break;
+	} else if (objc != 2) {
+	    Tcl_WrongNumArgs(interp, 2, objv, "?-command command?");
+	    result = TCL_ERROR;
+	    goto done;
+	}
+	if (textPtr->afterSyncCmd) {
+	    Tcl_DecrRefCount(textPtr->afterSyncCmd);
+	}
+	textPtr->afterSyncCmd = NULL;
+	TkTextUpdateLineMetrics(textPtr, 1,
+		TkBTreeNumLines(textPtr->sharedTextPtr->tree, textPtr), -1);
+	break;
+    }
     case TEXT_TAG:
 	result = TkTextTagCmd(textPtr, interp, objc, objv);
 	break;
@@ -1995,6 +2040,10 @@ DestroyText(
     textPtr->tkwin = NULL;
     textPtr->refCount--;
     Tcl_DeleteCommandFromToken(textPtr->interp, textPtr->widgetCmd);
+    if (textPtr->afterSyncCmd){
+	Tcl_DecrRefCount(textPtr->afterSyncCmd);
+	textPtr->afterSyncCmd = NULL;
+    }
     if (textPtr->refCount == 0) {
 	ckfree(textPtr);
     }
@@ -5368,6 +5417,52 @@ UpdateDirtyFlag(
 /*
  *----------------------------------------------------------------------
  *
+ * RunAfterSyncCmd --
+ *
+ *	This function is called by the event loop and executes the command
+ *      scheduled by [.text sync -command $cmd].
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Anything may happen, depending on $cmd contents.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+RunAfterSyncCmd(
+    ClientData clientData)		/* Information about text widget. */
+{
+    register TkText *textPtr = (TkText *) clientData;
+    int code;
+
+    if ((textPtr->tkwin == NULL) || (textPtr->flags & DESTROYED)) {
+        /*
+        * The widget has been deleted. Don't do anything.
+        */
+
+        if (--textPtr->refCount == 0) {
+            ckfree((char *) textPtr);
+        }
+        return;
+    }
+
+    Tcl_Preserve((ClientData) textPtr->interp);
+    code = Tcl_EvalObjEx(textPtr->interp, textPtr->afterSyncCmd, TCL_EVAL_GLOBAL);
+    if (code == TCL_ERROR) {
+        Tcl_AddErrorInfo(textPtr->interp, "\n    (text sync)");
+        Tcl_BackgroundError(textPtr->interp);
+    }
+    Tcl_Release((ClientData) textPtr->interp);
+    Tcl_DecrRefCount(textPtr->afterSyncCmd);
+    textPtr->afterSyncCmd = NULL;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
  * SearchPerform --
  *
  *	Overall control of search process. Is given a pattern, a starting
diff --git a/generic/tkText.h b/generic/tkText.h
index 78a99a9..fc92644 100644
--- a/generic/tkText.h
+++ b/generic/tkText.h
@@ -785,6 +785,8 @@ typedef struct TkText {
 				 * statements. */
     int autoSeparators;		/* Non-zero means the separators will be
 				 * inserted automatically. */
+    Tcl_Obj *afterSyncCmd;	/* Command to be executed when lines are up to
+                                 * date */
 } TkText;
 
 /*
@@ -1109,6 +1111,7 @@ MODULE_SCOPE int	TkTextMarkNameToIndex(TkText *textPtr,
 MODULE_SCOPE void	TkTextMarkSegToIndex(TkText *textPtr,
 			    TkTextSegment *markPtr, TkTextIndex *indexPtr);
 MODULE_SCOPE void	TkTextEventuallyRepick(TkText *textPtr);
+MODULE_SCOPE Bool	TkTextPendingsync(TkText *textPtr);
 MODULE_SCOPE void	TkTextPickCurrent(TkText *textPtr, XEvent *eventPtr);
 MODULE_SCOPE void	TkTextPixelIndex(TkText *textPtr, int x, int y,
 			    TkTextIndex *indexPtr, int *nearest);
diff --git a/generic/tkTextDisp.c b/generic/tkTextDisp.c
index a57c24b..18b373f 100644
--- a/generic/tkTextDisp.c
+++ b/generic/tkTextDisp.c
@@ -591,6 +591,7 @@ static int		TextGetScrollInfoObj(Tcl_Interp *interp,
 			    Tcl_Obj *const objv[], double *dblPtr,
 			    int *intPtr);
 static void		AsyncUpdateLineMetrics(ClientData clientData);
+static void		GenerateWidgetViewSyncEvent(TkText *textPtr, Bool InSync);
 static void		AsyncUpdateYScrollbar(ClientData clientData);
 static int              IsStartOfNotMergedLine(TkText *textPtr,
                             CONST TkTextIndex *indexPtr);
@@ -2941,6 +2942,8 @@ AsyncUpdateLineMetrics(
     lineNum = TkTextUpdateLineMetrics(textPtr, lineNum,
 	    dInfoPtr->lastMetricUpdateLine, 256);
 
+    dInfoPtr->currentMetricUpdateLine = lineNum;
+
     if (tkTextDebug) {
 	char buffer[2 * TCL_INTEGER_SPACE + 1];
 
@@ -2958,16 +2961,37 @@ AsyncUpdateLineMetrics(
 	/*
 	 * We have looped over all lines, so we're done. We must release our
 	 * refCount on the widget (the timer token was already set to NULL
-	 * above).
+	 * above). If there is a registered aftersync command, run that first.
 	 */
 
+        if (textPtr->afterSyncCmd) {
+            int code;
+            Tcl_Preserve((ClientData) textPtr->interp);
+            code = Tcl_EvalObjEx(textPtr->interp, textPtr->afterSyncCmd,
+                    TCL_EVAL_GLOBAL);
+	    if (code == TCL_ERROR) {
+                Tcl_AddErrorInfo(textPtr->interp, "\n    (text sync)");
+                Tcl_BackgroundError(textPtr->interp);
+	    }
+            Tcl_Release((ClientData) textPtr->interp);
+            Tcl_DecrRefCount(textPtr->afterSyncCmd);
+            textPtr->afterSyncCmd = NULL;
+	}
+
+        /*
+         * Fire the <<WidgetViewSync>> event since the widget view is in sync
+         * with its internal data (actually it will be after the next trip
+         * through the event loop, because the widget redraws at idle-time).
+         */
+
+        GenerateWidgetViewSyncEvent(textPtr, 1);
+
 	textPtr->refCount--;
 	if (textPtr->refCount == 0) {
 	    ckfree(textPtr);
 	}
 	return;
     }
-    dInfoPtr->currentMetricUpdateLine = lineNum;
 
     /*
      * Re-arm the timer. We already have a refCount on the text widget so no
@@ -2981,6 +3005,45 @@ AsyncUpdateLineMetrics(
 /*
  *----------------------------------------------------------------------
  *
+ * GenerateWidgetViewSyncEvent --
+ *
+ *      Send the <<WidgetViewSync>> event related to the text widget
+ *      line metrics asynchronous update.
+ *      This is equivalent to:
+ *         event generate $textWidget <<WidgetViewSync>> -detail $s
+ *      where $s is the sync status: true (when the widget view is in
+ *      sync with its internal data) or false (when it is not).
+ *
+ * Results:
+ *      None
+ *
+ * Side effects:
+ *      If corresponding bindings are present, they will trigger.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+GenerateWidgetViewSyncEvent(
+    TkText *textPtr,		/* Information about text widget. */
+    Bool InSync)                /* True if in sync, false otherwise */
+{
+    union {XEvent general; XVirtualEvent virtual;} event;
+
+    memset(&event, 0, sizeof(event));
+    event.general.xany.type = VirtualEvent;
+    event.general.xany.serial = NextRequest(Tk_Display(textPtr->tkwin));
+    event.general.xany.send_event = False;
+    event.general.xany.window = Tk_WindowId(textPtr->tkwin);
+    event.general.xany.display = Tk_Display(textPtr->tkwin);
+    event.virtual.name = Tk_GetUid("WidgetViewSync");
+    event.virtual.user_data = Tcl_NewBooleanObj(InSync);
+    Tk_HandleEvent(&event.general);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
  * TkTextUpdateLineMetrics --
  *
  *	This function updates the pixel height calculations of a range of
@@ -3353,6 +3416,7 @@ TextInvalidateLineMetrics(
 	textPtr->refCount++;
 	dInfoPtr->lineUpdateTimer = Tcl_CreateTimerHandler(1,
 		AsyncUpdateLineMetrics, textPtr);
+        GenerateWidgetViewSyncEvent(textPtr, 0);
     }
 }
 
@@ -5064,6 +5128,7 @@ TkTextRelayoutWindow(
 	    textPtr->refCount++;
 	    dInfoPtr->lineUpdateTimer = Tcl_CreateTimerHandler(1,
 		    AsyncUpdateLineMetrics, textPtr);
+            GenerateWidgetViewSyncEvent(textPtr, 0);
 	}
     }
 }
@@ -6066,6 +6131,35 @@ TkTextYviewCmd(
 /*
  *--------------------------------------------------------------
  *
+ * TkTextPendingsync --
+ *
+ *	This function checks if any line heights are not up-to-date.
+ *
+ * Results:
+ *	Returns a boolean true if it is the case, or false if all line
+ *      heights are up-to-date.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+Bool
+TkTextPendingsync(
+    TkText *textPtr)		/* Information about text widget. */
+{
+    TextDInfo *dInfoPtr = textPtr->dInfoPtr;
+
+    return (
+        ((dInfoPtr->metricEpoch == -1) &&
+         (dInfoPtr->lastMetricUpdateLine == dInfoPtr->currentMetricUpdateLine)) ?
+        0 : 1);
+}
+
+/*
+ *--------------------------------------------------------------
+ *
  * TkTextScanCmd --
  *
  *	This function is invoked to process the "scan" option for the widget
diff --git a/tests/text.test b/tests/text.test
index 7ade29a..52a21af 100644
--- a/tests/text.test
+++ b/tests/text.test
@@ -925,7 +925,7 @@ test text-3.2 {TextWidgetCmd procedure} -setup {
     .t gorp 1.0 z 1.2
 } -cleanup {
     destroy .t
-} -returnCodes {error} -result {bad option "gorp": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, replace, scan, search, see, tag, window, xview, or yview}
+} -returnCodes {error} -result {bad option "gorp": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, pendingsync, replace, scan, search, see, sync, tag, window, xview, or yview}
 
 test text-4.1 {TextWidgetCmd procedure, "bbox" option} -setup {
     text .t
@@ -1147,7 +1147,7 @@ Line 7"
     .t co 1.0 z 1.2
 } -cleanup {
     destroy .t
-} -returnCodes {error} -result {ambiguous option "co": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, replace, scan, search, see, tag, window, xview, or yview}
+} -returnCodes {error} -result {ambiguous option "co": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, pendingsync, replace, scan, search, see, sync, tag, window, xview, or yview}
 # "configure" option is already covered above
 
 test text-7.1 {TextWidgetCmd procedure, "debug" option} -setup {
@@ -1163,7 +1163,7 @@ test text-7.2 {TextWidgetCmd procedure, "debug" option} -setup {
     .t de 0 1
 } -cleanup {
     destroy .t
-} -returnCodes {error} -result {ambiguous option "de": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, replace, scan, search, see, tag, window, xview, or yview}
+} -returnCodes {error} -result {ambiguous option "de": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, pendingsync, replace, scan, search, see, sync, tag, window, xview, or yview}
 test text-7.3 {TextWidgetCmd procedure, "debug" option} -setup {
     text .t
 } -body {
@@ -2686,7 +2686,7 @@ test text-9.2.47 {TextWidgetCmd procedure, "count" option} -setup {
     # next line to be fully sure that asynchronous line heights calculation is
     # up-to-date otherwise this test may fail (depending on the computer
     # performance), especially when the . toplevel has small height
-    .t count -update -ypixels 1.0 end
+    .t sync
     set y1 [lindex [.t yview] 1]
     .t count -displaylines 5.0 11.0
     set y2 [lindex [.t yview] 1]
@@ -2882,6 +2882,176 @@ test text-11.9 {counting with tag priority eliding} -setup {
     destroy .t
 } -result {1 0 0 1 0 2.0 4.0 4.0 4.0 3.0 3.0 3.0 2.0 1.0 1.0}
 
+test text-11a.1 {TextWidgetCmd procedure, "pendingsync" option} -setup {
+    destroy .yt
+} -body {
+    text .yt
+    list [catch {.yt pendingsync mytext} msg] $msg
+} -cleanup {
+    destroy .yt
+} -result {1 {wrong # args: should be ".yt pendingsync"}}
+test text-11a.2 {TextWidgetCmd procedure, "pendingsync" option} -setup {
+    destroy .top.yt .top
+} -body {
+    toplevel .top
+    pack [text .top.yt]
+    set content {}
+    for {set i 1} {$i < 300} {incr i} {
+        append content [string repeat "$i " 15] \n
+    }
+    .top.yt insert 1.0 $content
+    # wait for end of line metrics calculation to get correct $fraction1
+    # as a reference
+    while {[.top.yt pendingsync]} {update}
+    .top.yt yview moveto 1
+    set fraction1 [lindex [.top.yt yview] 0]
+    set res [expr {$fraction1 > 0}]
+    .top.yt delete 1.0 end
+    .top.yt insert 1.0 $content
+    # ensure the test is relevant
+    lappend res [.top.yt pendingsync]
+    # asynchronously wait for completion of line metrics calculation
+    while {[.top.yt pendingsync]} {update}
+    .top.yt yview moveto $fraction1
+    set fraction2 [lindex [.top.yt yview] 0]
+    lappend res [expr {$fraction1 == $fraction2}]
+} -cleanup {
+    destroy .top.yt .top
+} -result {1 1 1}
+
+test text-11a.11 {TextWidgetCmd procedure, "sync" option} -setup {
+    destroy .yt
+} -body {
+    text .yt
+    list [catch {.yt sync mytext} msg] $msg
+} -cleanup {
+    destroy .yt
+} -result {1 {wrong # args: should be ".yt sync ?-command command?"}}
+test text-11a.12 {TextWidgetCmd procedure, "sync" option} -setup {
+    destroy .top.yt .top
+} -body {
+    toplevel .top
+    pack [text .top.yt]
+    set content {}
+    for {set i 1} {$i < 30} {incr i} {
+        append content [string repeat "$i " 15] \n
+    }
+    .top.yt insert 1.0 $content
+    # wait for end of line metrics calculation to get correct $fraction1
+    # as a reference
+    .top.yt sync
+    .top.yt yview moveto 1
+    set fraction1 [lindex [.top.yt yview] 0]
+    set res [expr {$fraction1 > 0}]
+    # first case: do not wait for completion of line metrics calculation
+    .top.yt delete 1.0 end
+    .top.yt insert 1.0 $content
+    .top.yt yview moveto $fraction1
+    set fraction2 [lindex [.top.yt yview] 0]
+    lappend res [expr {$fraction1 == $fraction2}]
+    # second case: wait for completion of line metrics calculation
+    .top.yt delete 1.0 end
+    .top.yt insert 1.0 $content
+    .top.yt sync
+    .top.yt yview moveto $fraction1
+    set fraction2 [lindex [.top.yt yview] 0]
+    lappend res [expr {$fraction1 == $fraction2}]
+} -cleanup {
+    destroy .top.yt .top
+} -result {1 0 1}
+
+test text-11a.21 {TextWidgetCmd procedure, "sync" option with -command} -setup {
+    destroy .yt
+} -body {
+    text .yt
+    list [catch {.yt sync -comx foo} msg] $msg
+} -cleanup {
+    destroy .yt
+} -result {1 {wrong option "-comx": should be "-command"}}
+test text-11a.22 {TextWidgetCmd procedure, "sync" option with -command} -setup {
+    destroy .top.yt .top
+} -body {
+    set res {}
+    set ::x 0
+    toplevel .top
+    pack [text .top.yt]
+    set content {}
+    for {set i 1} {$i < 30} {incr i} {
+        append content [string repeat "$i " 15] \n
+    }
+    .top.yt insert 1.0 $content
+    # first case: line metrics calculation still running when launching 'sync -command'
+    lappend res [.top.yt pendingsync]
+    .top.yt sync -command [list set ::x 1]
+    lappend res $::x
+    # now finish line metrics calculations
+    while {[.top.yt pendingsync]} {update}
+    lappend res [.top.yt pendingsync] $::x
+    # second case: line metrics calculation completed when launching 'sync -command'
+    .top.yt sync -command [list set ::x 2]
+    lappend res $::x
+    vwait ::x
+    lappend res $::x
+} -cleanup {
+    destroy .top.yt .top
+} -result {1 0 0 1 1 2}
+
+test text-11a.31 {"<<WidgetViewSync>>" event} -setup {
+    destroy .top.yt .top
+} -body {
+    toplevel .top
+    pack [text .top.yt]
+    set content {}
+    for {set i 1} {$i < 300} {incr i} {
+        append content [string repeat "$i " 15] \n
+    }
+    .top.yt insert 1.0 $content
+    update
+    bind .top.yt <<WidgetViewSync>> { if {%d} {set yud(%W) 1} }
+    # wait for end of line metrics calculation to get correct $fraction1
+    # as a reference
+    if {[.top.yt pendingsync]} {vwait yud(.top.yt)}
+    .top.yt yview moveto 1
+    set fraction1 [lindex [.top.yt yview] 0]
+    set res [expr {$fraction1 > 0}]
+    .top.yt delete 1.0 end
+    .top.yt insert 1.0 $content
+    # synchronously wait for completion of line metrics calculation
+    # and ensure the test is relevant
+    set waited 0
+    if {[.top.yt pendingsync]} {set waited 1 ; vwait yud(.top.yt)}
+    lappend res $waited
+    .top.yt yview moveto $fraction1
+    set fraction2 [lindex [.top.yt yview] 0]
+    lappend res [expr {$fraction1 == $fraction2}]
+} -cleanup {
+    destroy .top.yt .top
+} -result {1 1 1}
+
+test text-11a.41 {"sync" "pendingsync" and <<WidgetViewSync>>} -setup {
+    destroy .top.yt .top
+} -body {
+    set res {}
+    toplevel .top
+    pack [text .top.yt]
+    set content {}
+    for {set i 1} {$i < 300} {incr i} {
+        append content [string repeat "$i " 50] \n
+    }
+    bind .top.yt <<WidgetViewSync>> {lappend res Sync:%d}
+    .top.yt insert 1.0 $content
+    vwait res  ; # event dealt with by the event loop, with %d==0 i.e. we're out of sync
+    # ensure the test is relevant
+    lappend res "Pending:[.top.yt pendingsync]"
+    # - <<WidgetViewSync>> fires when sync returns if there was pending syncs 
+    # - there is no more any pending sync after running 'sync'
+    .top.yt sync
+    vwait res  ; # event dealt with by the event loop, with %d==1 i.e. we're in sync again
+    lappend res "Pending:[.top.yt pendingsync]"
+    set res
+} -cleanup {
+    destroy .top.yt .top
+} -result {Sync:0 Pending:1 Sync:1 Pending:0}
 
 test text-12.1 {TextWidgetCmd procedure, "index" option} -setup {
     text .t
@@ -2903,7 +3073,7 @@ test text-12.3 {TextWidgetCmd procedure, "index" option} -setup {
     .t in a b
 } -cleanup {
     destroy .t
-} -returnCodes {error} -result {ambiguous option "in": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, replace, scan, search, see, tag, window, xview, or yview}
+} -returnCodes {error} -result {ambiguous option "in": must be bbox, cget, compare, configure, count, debug, delete, dlineinfo, dump, edit, get, image, index, insert, mark, peer, pendingsync, replace, scan, search, see, sync, tag, window, xview, or yview}
 test text-12.4 {TextWidgetCmd procedure, "index" option} -setup {
     text .t
 } -body {
@@ -6710,7 +6880,7 @@ test text-33.2 {TextWidgetCmd procedure, "peer" option} -setup {
 test text-33.3 {TextWidgetCmd procedure, "peer" option} -setup {
     text .t
 } -body {
-    .t p names
+    .t pee names
 } -cleanup {
     destroy .t
 } -returnCodes {ok} -result {}
diff --git a/tests/textDisp.test b/tests/textDisp.test
index ac3aee0..caba769 100644
--- a/tests/textDisp.test
+++ b/tests/textDisp.test
@@ -4197,29 +4197,34 @@ test textDisp-33.5 {bold or italic fonts} win {
 } {italic font measurement ok}
 destroy .tt
 
-test textDisp-34.1 {Text widgets multi-scrolling problem: Bug 2677890} -setup {
-    pack [text .t1 -width 10 -yscrollcommand {.sy set}] \
-	[ttk::scrollbar .sy -orient vertical -command {.t1 yview}] \
-	-side left -fill both
-    bindtags .sy {}; # No clicky!
+test textDisp-34.1 {Line heights recalculation problem: bug 2677890} -setup {
+    pack [text .t1] -expand 1 -fill both
     set txt ""
-    for {set i 0} {$i < 99} {incr i} {
-	lappend txt "$i" [list pc $i] "\n" ""
+    for {set i 1} {$i < 100} {incr i} {
+        append txt "Line $i\n"
     }
     set result {}
 } -body {
-    .t1 insert end {*}$txt
-    update
-    lappend result [.sy get]
-    .t1 replace 6.0 6.0+1c "*"
-    lappend result [.sy get]
-    after 0 {lappend result [.sy get]}
-    after 1000 {lappend result [.sy get]}
-    vwait result;vwait result
-    return $result
+    .t1 insert end $txt
+    .t1 debug 1
+    set ge [winfo geometry .]
+    scan $ge "%dx%d+%d+%d" width height left top
+    update
+    .t1 sync
+    set negative 0
+    bind .t1 <<WidgetViewSync>> { if {%d < 0} {set negative 1} }
+    # Without the fix for bug 2677890, changing the width of the toplevel
+    # will launch recomputation of the line heights, but will produce negative
+    # number of still remaining outdated lines, which is obviously wrong.
+    # Thus we use this way to check for regression regarding bug 2677890,
+    # i.e. to check that the fix for this bug really is still in.
+    wm geometry . "[expr {$width * 2}]x$height+$left+$top"
+    update
+    .t1 sync
+    set negative
 } -cleanup {
-    destroy .t1 .sy
-} -result {{0.0 0.24} {0.0 0.24} {0.0 0.24} {0.0 0.24}}
+    destroy .t1
+} -result {0}
 
 test textDisp-35.1 {Init value of charHeight - Dancing scrollbar bug 1499165} -setup {
     pack [text .t1] -fill both -expand y -side left