git-gui: Preserve scroll position on reshow_diff.

It is especially useful for Stage/Unstage Line, because
they invoke full state scan and diff reload, which originally
would reset the scroll position to the top of the file.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/lib/diff.tcl b/lib/diff.tcl
index 77990c537c9d068fdcdf62a83b8c132399dff749..52b79e4a1f476c2ee9b65087f66a352a25ed0903 100644 (file)
--- a/lib/diff.tcl
+++ b/lib/diff.tcl
@@ -19,6 +19,7 @@ proc clear_diff {} {
 proc reshow_diff {} {
        global file_states file_lists
        global current_diff_path current_diff_side
+       global ui_diff
 
        set p $current_diff_path
        if {$p eq {}} {
@@ -28,7 +29,8 @@ proc reshow_diff {} {
                || [lsearch -sorted -exact $file_lists($current_diff_side) $p] == -1} {
                clear_diff
        } else {
-               show_diff $p $current_diff_side
+               set save_pos [lindex [$ui_diff yview] 0]
+               show_diff $p $current_diff_side {} $save_pos
        }
 }
 
@@ -52,7 +54,7 @@ A rescan will be automatically started to find other files which may have the sa
        rescan ui_ready 0
 }
 
-proc show_diff {path w {lno {}}} {
+proc show_diff {path w {lno {}} {scroll_pos {}}} {
        global file_states file_lists
        global is_3way_diff diff_active repo_config
        global ui_diff ui_index ui_workdir
@@ -151,6 +153,10 @@ proc show_diff {path w {lno {}}} {
                $ui_diff conf -state disabled
                set diff_active 0
                unlock_index
+               if {$scroll_pos ne {}} {
+                       update
+                       $ui_diff yview moveto $scroll_pos
+               }
                ui_ready
                return
        }
@@ -190,10 +196,10 @@ proc show_diff {path w {lno {}}} {
                -blocking 0 \
                -encoding binary \
                -translation binary
-       fileevent $fd readable [list read_diff $fd]
+       fileevent $fd readable [list read_diff $fd $scroll_pos]
 }
 
-proc read_diff {fd} {
+proc read_diff {fd scroll_pos} {
        global ui_diff diff_active
        global is_3way_diff current_diff_header
 
@@ -282,6 +288,10 @@ proc read_diff {fd} {
                close $fd
                set diff_active 0
                unlock_index
+               if {$scroll_pos ne {}} {
+                       update
+                       $ui_diff yview moveto $scroll_pos
+               }
                ui_ready
 
                if {[$ui_diff index end] eq {2.0}} {