gitk: Fix problems with target row stuff

Occasionally the target row stuff would scroll the display to some
uninteresting commit while reading.  There were two problems: one
was that drawvisible would set targetrow even if there was no target
previously and no row selected, and the other was that it was possible
for the target row to get pushed down past numcommits, if drawvisible
was called after rows were added but before layoutmore got run.

The first problem is fixed by just not setting targetrow/id unless
there is a selected row or they were set previously.

The second problem is fixed by updating numcommits immediately new
rows are added.  This leads to a simplification of layoutmore and
chewcommits but also means that some of the things that were done in
layoutmore now need to be done elsewhere, since layoutmore can no
longer use numcommits to know how much it has seen previously.
Hence the changes to getcommits, initlayout and setcanvscroll.

Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -161,11 +161,12 @@ proc stop_rev_list {view} {
 }
 
 proc getcommits {} {
-    global canv curview
+    global canv curview need_redisplay
 
     initlayout
     start_rev_list $curview
     show_status [mc "Reading commits..."]
+    set need_redisplay 1
 }
 
 proc updatecommits {} {
@@ -1048,7 +1049,7 @@ proc getcommitlines {fd inst view updating}  {
 	    adjustprogress
 	}
 	if {$view == $curview} {
-	    run chewcommits $view
+	    run chewcommits
 	}
 	return 0
     }
@@ -1183,7 +1184,16 @@ proc getcommitlines {fd inst view updating}  {
 	set gotsome 1
     }
     if {$gotsome} {
-	run chewcommits $view
+	global numcommits hlview
+
+	if {$view == $curview} {
+	    set numcommits $commitidx($view)
+	    run chewcommits
+	}
+	if {[info exists hlview] && $view == $hlview} {
+	    # we never actually get here...
+	    run vhighlightmore
+	}
 	foreach s $scripts {
 	    eval $s
 	}
@@ -1218,13 +1228,12 @@ proc getcommitlines {fd inst view updating}  {
     return 2
 }
 
-proc chewcommits {view} {
+proc chewcommits {} {
     global curview hlview viewcomplete
     global pending_select
 
-    if {$view == $curview} {
     layoutmore
-	if {$viewcomplete($view)} {
+    if {$viewcomplete($curview)} {
 	global commitidx varctok
 	global numcommits startmsecs
 	global mainheadid commitinfo nullid
@@ -1242,10 +1251,6 @@ proc chewcommits {view} {
 	}
 	notbusy layout
     }
-    }
-    if {[info exists hlview] && $view == $hlview} {
-	vhighlightmore
-    }
     return 0
 }
 
@@ -3064,6 +3069,7 @@ proc vhighlightmore {} {
 	}
     }
     set vhl_done $max
+    return 0
 }
 
 proc askvhighlight {row id} {
@@ -3562,15 +3568,19 @@ proc initlayout {} {
     set canvxmax [$canv cget -width]
     catch {unset colormap}
     catch {unset rowtextx}
+    setcanvscroll
 }
 
 proc setcanvscroll {} {
     global canv canv2 canv3 numcommits linespc canvxmax canvy0
+    global lastscrollset lastscrollrows
 
     set ymax [expr {$canvy0 + ($numcommits - 0.5) * $linespc + 2}]
     $canv conf -scrollregion [list 0 0 $canvxmax $ymax]
     $canv2 conf -scrollregion [list 0 0 0 $ymax]
     $canv3 conf -scrollregion [list 0 0 0 $ymax]
+    set lastscrollset [clock clicks -milliseconds]
+    set lastscrollrows $numcommits
 }
 
 proc visiblerows {} {
@@ -3595,33 +3605,17 @@ proc visiblerows {} {
 proc layoutmore {} {
     global commitidx viewcomplete curview
     global numcommits pending_select selectedline curview
-    global lastscrollset commitinterest
+    global lastscrollset lastscrollrows commitinterest
 
-    set canshow $commitidx($curview)
+    if {$lastscrollrows < 100 || $viewcomplete($curview) ||
-    if {$canshow <= $numcommits && !$viewcomplete($curview)} return
+	[clock clicks -milliseconds] - $lastscrollset > 500} {
-    if {$numcommits == 0} {
-	allcanvs delete all
-    }
-    set r0 $numcommits
-    set prev $numcommits
-    set numcommits $canshow
-    set t [clock clicks -milliseconds]
-    if {$prev < 100 || $viewcomplete($curview) || $t - $lastscrollset > 500} {
-	set lastscrollset $t
 	setcanvscroll
     }
-    set rows [visiblerows]
-    set r1 [lindex $rows 1]
-    if {$r1 >= $canshow} {
-	set r1 [expr {$canshow - 1}]
-    }
-    if {$r0 <= $r1} {
-	drawcommits $r0 $r1
-    }
     if {[info exists pending_select] &&
 	[commitinview $pending_select $curview]} {
 	selectline [rowofcommit $pending_select] 1
     }
+    drawvisible
 }
 
 proc doshowlocalchanges {} {
@@ -4714,13 +4708,15 @@ proc drawvisible {} {
     if {[info exists selectedline] &&
 	$row <= $selectedline && $selectedline <= $endrow} {
 	set targetrow $selectedline
-    } else {
+    } elseif {[info exists targetid]} {
 	set targetrow [expr {int(($row + $endrow) / 2)}]
     }
+    if {[info exists targetrow]} {
 	if {$targetrow >= $numcommits} {
 	    set targetrow [expr {$numcommits - 1}]
 	}
 	set targetid [commitonrow $targetrow]
+    }
     drawcommits $row $endrow
 }
 
@@ -5459,6 +5455,10 @@ proc selectline {l isnew} {
     unsel_reflist
     stopfinding
     if {$l < 0 || $l >= $numcommits} return
+    set id [commitonrow $l]
+    set targetid $id
+    set targetrow $l
+
     set y [expr {$canvy0 + $l * $linespc}]
     set ymax [lindex [$canv cget -scrollregion] 3]
     set ytop [expr {$y - $linespc - 1}]
@@ -5497,15 +5497,12 @@ proc selectline {l isnew} {
 
     make_secsel $l
 
-    set id [commitonrow $l]
     if {$isnew} {
 	addtohistory [list selbyid $id]
     }
 
     set selectedline $l
     set currentid $id
-    set targetid $id
-    set targetrow $l
     $sha1entry delete 0 end
     $sha1entry insert 0 $id
     $sha1entry selection from 0