gitk: Improve the drawing of links to parent lines

The way gitk used to draw the lines joining a commit to the lines
representing its parents was sometimes visually ambiguous, especially
when the line to the parent had a corner that coincided with a corner
on another line.

This improves things by using a smaller slanting section on the line
joining a commit to a parent line if the parent line is vertical where
it joins on.  It also optimizes the drawing a little in the case where
the parent line slants towards this commit already.

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

diff --git a/gitk b/gitk
index 40e5d31749c17a865780ec554a3cab3e0952b72b..bc3022e69fe107c4dfa3a736b0360293722a55a7 100755 (executable)
--- a/gitk
+++ b/gitk
@@ -3363,7 +3363,7 @@ proc drawlineseg {id row endrow arrowlow} {
 
 proc drawparentlinks {id row} {
     global rowidlist canv colormap curview parentlist
-    global idpos
+    global idpos linespc
 
     set rowids [lindex $rowidlist $row]
     set col [lsearch -exact $rowids $id]
@@ -3373,6 +3373,8 @@ proc drawparentlinks {id row} {
     set x [xc $row $col]
     set y [yc $row]
     set y2 [yc $row2]
+    set d [expr {int(0.4 * $linespc)}]
+    set ymid [expr {$y + $d}]
     set ids [lindex $rowidlist $row2]
     # rmx = right-most X coord used
     set rmx 0
@@ -3386,19 +3388,37 @@ proc drawparentlinks {id row} {
        if {$x2 > $rmx} {
            set rmx $x2
        }
-       if {[lsearch -exact $rowids $p] < 0} {
+       set j [lsearch -exact $rowids $p]
+       if {$j < 0} {
            # drawlineseg will do this one for us
            continue
        }
        assigncolor $p
        # should handle duplicated parents here...
        set coords [list $x $y]
-       if {$i < $col - 1} {
-           lappend coords [xc $row [expr {$i + 1}]] $y
-       } elseif {$i > $col + 1} {
-           lappend coords [xc $row [expr {$i - 1}]] $y
+       if {$i != $col} {
+           # if attaching to a vertical segment, draw a smaller
+           # slant for visual distinctness
+           if {$i == $j} {
+               if {$i < $col} {
+                   lappend coords [expr {$x2 + $d}] $y $x2 $ymid
+               } else {
+                   lappend coords [expr {$x2 - $d}] $y $x2 $ymid
+               }
+           } elseif {$i < $col && $i < $j} {
+               # segment slants towards us already
+               lappend coords [xc $row $j] $y
+           } else {
+               if {$i < $col - 1} {
+                   lappend coords [expr {$x2 + $linespc}] $y
+               } elseif {$i > $col + 1} {
+                   lappend coords [expr {$x2 - $linespc}] $y
+               }
+               lappend coords $x2 $y2
+           }
+       } else {
+           lappend coords $x2 $y2
        }
-       lappend coords $x2 $y2
        set t [$canv create line $coords -width [linewidth $p] \
                   -fill $colormap($p) -tags lines.$p]
        $canv lower $t