[PATCH] gitk: Handle MouseWheel events on Windows

Windows, unlike X-Windows, sends mousewheel events by default to the
window that has keyboard focus and uses the MouseWheel event to do so.
The window to be scrolled must be able to take focus, but gitk's panels
are disabled so cannot take focus.  For all these reasons, a different
design is needed to use the mousewheel on Windows.  The approach here is
to bind the mousewheel events to the top level window and redirect them
based upon the current mouse position.

Signed-off-by: Mark Levedahl <mdl123@verizon.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -823,8 +823,13 @@ proc makewindow {} {
     pack .ctop -fill both -expand 1
     bindall <1> {selcanvline %W %x %y}
     #bindall <B1-Motion> {selcanvline %W %x %y}
-    bindall <ButtonRelease-4> "allcanvs yview scroll -5 units"
-    bindall <ButtonRelease-5> "allcanvs yview scroll 5 units"
+    if {[tk windowingsystem] == "win32"} {
+	bind . <MouseWheel> { windows_mousewheel_redirector %W %X %Y %D }
+	bind $ctext <MouseWheel> { windows_mousewheel_redirector %W %X %Y %D ; break }
+    } else {
+	bindall <ButtonRelease-4> "allcanvs yview scroll -5 units"
+	bindall <ButtonRelease-5> "allcanvs yview scroll 5 units"
+    }
     bindall <2> "canvscan mark %W %x %y"
     bindall <B2-Motion> "canvscan dragto %W %x %y"
     bindkey <Home> selfirstline
@@ -927,6 +932,24 @@ proc makewindow {} {
 	-command {flist_hl 1}
 }
 
+# Windows sends all mouse wheel events to the current focused window, not
+# the one where the mouse hovers, so bind those events here and redirect
+# to the correct window
+proc windows_mousewheel_redirector {W X Y D} {
+    global canv canv2 canv3
+    set w [winfo containing -displayof $W $X $Y]
+    if {$w ne ""} {
+	set u [expr {$D < 0 ? 5 : -5}]
+	if {$w == $canv || $w == $canv2 || $w == $canv3} {
+	    allcanvs yview scroll $u units
+	} else {
+	    catch {
+		$w yview scroll $u units
+	    }
+	}
+    }
+}
+
 # mouse-2 makes all windows scan vertically, but only the one
 # the cursor is in scans horizontally
 proc canvscan {op w x y} {