gitk: Fix transient windows on Win32 and MacOS

Transient windows cause problems on these platforms:

- On Win32 the windows appear in the top left corner
  of the screen. In order to fix it, this patch causes
  them to be explicitly centered on their parents by
  an idle handler.

- On MacOS with Tk 8.4 they appear without a title bar.
  Since it is clearly unacceptable, this patch disables
  transient on that platform.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -1739,6 +1739,24 @@ proc removehead {id name} {
     unset headids($name)
 }
 
+proc make_transient {window origin} {
+    global have_tk85
+
+    # In MacOS Tk 8.4 transient appears to work by setting
+    # overrideredirect, which is utterly useless, since the
+    # windows get no border, and are not even kept above
+    # the parent.
+    if {!$have_tk85 && [tk windowingsystem] eq {aqua}} return
+
+    wm transient $window $origin
+
+    # Windows fails to place transient windows normally, so
+    # schedule a callback to center them on the parent.
+    if {[tk windowingsystem] eq {win32}} {
+	after idle [list tk::PlaceWindow $window widget $origin]
+    }
+}
+
 proc show_error {w top msg} {
     message $w.m -text $msg -justify center -aspect 400
     pack $w.m -side top -fill x -padx 20 -pady 20
@@ -1754,7 +1772,7 @@ proc show_error {w top msg} {
 proc error_popup {msg {owner .}} {
     set w .error
     toplevel $w
-    wm transient $w $owner
+    make_transient $w $owner
     show_error $w $w $msg
 }
 
@@ -1763,7 +1781,7 @@ proc confirm_popup {msg {owner .}} {
     set confirm_ok 0
     set w .confirm
     toplevel $w
-    wm transient $w $owner
+    make_transient $w $owner
     message $w.m -text $msg -justify center -aspect 400
     pack $w.m -side top -fill x -padx 20 -pady 20
     button $w.ok -text [mc OK] -command "set confirm_ok 1; destroy $w"
@@ -2558,7 +2576,7 @@ proc about {} {
     }
     toplevel $w
     wm title $w [mc "About gitk"]
-    wm transient $w .
+    make_transient $w .
     message $w.m -text [mc "
 Gitk - a commit viewer for git
 
@@ -2587,7 +2605,7 @@ proc keys {} {
     }
     toplevel $w
     wm title $w [mc "Gitk key bindings"]
-    wm transient $w .
+    make_transient $w .
     message $w.m -text "
 [mc "Gitk key bindings:"]
 
@@ -3669,7 +3687,7 @@ proc vieweditor {top n title} {
 
     toplevel $top
     wm title $top $title
-    wm transient $top .
+    make_transient $top .
 
     # View name
     frame $top.nfr
@@ -7912,7 +7930,7 @@ proc mkpatch {} {
     set patchtop $top
     catch {destroy $top}
     toplevel $top
-    wm transient $top .
+    make_transient $top .
     label $top.title -text [mc "Generate patch"]
     grid $top.title - -pady 10
     label $top.from -text [mc "From:"]
@@ -7999,7 +8017,7 @@ proc mktag {} {
     set mktagtop $top
     catch {destroy $top}
     toplevel $top
-    wm transient $top .
+    make_transient $top .
     label $top.title -text [mc "Create tag"]
     grid $top.title - -pady 10
     label $top.id -text [mc "ID:"]
@@ -8102,7 +8120,7 @@ proc writecommit {} {
     set wrcomtop $top
     catch {destroy $top}
     toplevel $top
-    wm transient $top .
+    make_transient $top .
     label $top.title -text [mc "Write commit to file"]
     grid $top.title - -pady 10
     label $top.id -text [mc "ID:"]
@@ -8159,7 +8177,7 @@ proc mkbranch {} {
     set top .makebranch
     catch {destroy $top}
     toplevel $top
-    wm transient $top .
+    make_transient $top .
     label $top.title -text [mc "Create new branch"]
     grid $top.title - -pady 10
     label $top.id -text [mc "ID:"]
@@ -8322,7 +8340,7 @@ proc resethead {} {
     set confirm_ok 0
     set w ".confirmreset"
     toplevel $w
-    wm transient $w .
+    make_transient $w .
     wm title $w [mc "Confirm reset"]
     message $w.m -text \
 	[mc "Reset branch %s to %s?" $mainhead [string range $rowmenuid 0 7]] \
@@ -8502,7 +8520,7 @@ proc showrefs {} {
     }
     toplevel $top
     wm title $top [mc "Tags and heads: %s" [file tail [pwd]]]
-    wm transient $top .
+    make_transient $top .
     text $top.list -background $bgcolor -foreground $fgcolor \
 	-selectbackground $selectbgcolor -font mainfont \
 	-xscrollcommand "$top.xsb set" -yscrollcommand "$top.ysb set" \
@@ -9844,7 +9862,7 @@ proc choosefont {font which} {
 	font create sample
 	eval font config sample [font actual $font]
 	toplevel $top
-	wm transient $top $prefstop
+	make_transient $top $prefstop
 	wm title $top [mc "Gitk font chooser"]
 	label $top.l -textvariable fontparam(which)
 	pack $top.l -side top
@@ -9961,7 +9979,7 @@ proc doprefs {} {
     }
     toplevel $top
     wm title $top [mc "Gitk preferences"]
-    wm transient $top .
+    make_transient $top .
     label $top.ldisp -text [mc "Commit list display options"]
     grid $top.ldisp - -sticky w -pady 10
     label $top.spacer -text " "