git-gui: Assign background colors to each blame hunk.

To help the user visually see which lines are associated with each other
in the file we attempt to sign a unique background color to each commit
and then render all text associated with that commit using that color.

This works out OK for a file which has very few commits in it; but
most files don't have that property.

What we really need to do is look at what colors are used by our
neighboring commits (if known yet) and pick a color which does not
conflict with our neighbor.  If we have run out of colors then we
should force our neighbor to recolor too.  Yes, its the graph coloring
problem.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -3309,6 +3309,8 @@ proc show_blame {commit path} {
 		"
 	}
 
+	set blame_data($w,colors) {}
+
 	bind $w <Visibility> "focus $w"
 	bind $w <Destroy> "
 		array unset blame_status $w
@@ -3366,6 +3368,15 @@ proc read_blame_incremental {fd w
 		return
 	}
 
+	set all [list \
+		$w_commit \
+		$w_author \
+		$w_date \
+		$w_filename \
+		$w_olno \
+		$w_lno \
+		$w_file]
+
 	$w_commit conf -state normal
 	$w_author conf -state normal
 	$w_date conf -state normal
@@ -3374,36 +3385,65 @@ proc read_blame_incremental {fd w
 
 	while {[gets $fd line] >= 0} {
 		if {[regexp {^([a-z0-9]{40}) (\d+) (\d+) (\d+)$} $line line \
-			commit original_line final_line line_count]} {
-			set blame_data($w,commit) $commit
+			cmit original_line final_line line_count]} {
+			set blame_data($w,commit) $cmit
 			set blame_data($w,original_line) $original_line
 			set blame_data($w,final_line) $final_line
 			set blame_data($w,line_count) $line_count
+
+			if {[catch {set g $blame_data($w,$cmit,seen)}]} {
+				if {$blame_data($w,colors) eq {}} {
+					set blame_data($w,colors) {
+						yellow
+						red
+						pink
+						orange
+						green
+						grey
+					}
+				}
+				set c [lindex $blame_data($w,colors) 0]
+				set blame_data($w,colors) \
+					[lrange $blame_data($w,colors) 1 end]
+				foreach t $all {
+					$t tag conf g$cmit -background $c
+				}
+			} else {
+				set blame_data($w,$cmit,seen) 1
+			}
 		} elseif {[string match {filename *} $line]} {
 			set n $blame_data($w,line_count)
 			set lno $blame_data($w,final_line)
 			set ol $blame_data($w,original_line)
 			set file [string range $line 9 end]
-			set commit $blame_data($w,commit)
-			set abbrev [string range $commit 0 8]
+			set cmit $blame_data($w,commit)
+			set abbrev [string range $cmit 0 8]
 
-			if {[catch {set author $blame_data($w,$commit,author)} err]} {
-			puts $err
+			if {[catch {set author $blame_data($w,$cmit,author)} err]} {
 				set author {}
 			}
 
-			if {[catch {set atime $blame_data($w,$commit,author-time)}]} {
+			if {[catch {set atime $blame_data($w,$cmit,author-time)}]} {
 				set atime {}
 			} else {
 				set atime [clock format $atime -format {%Y-%m-%d %T}]
 			}
 
 			while {$n > 0} {
-				$w_commit delete $lno.0 "$lno.0 lineend"
-				$w_author delete $lno.0 "$lno.0 lineend"
-				$w_date delete $lno.0 "$lno.0 lineend"
-				$w_filename delete $lno.0 "$lno.0 lineend"
-				$w_olno delete $lno.0 "$lno.0 lineend"
+				if {![catch {set g g$blame_data($w,line$lno,commit)}]} {
+					foreach t $all {
+						$t tag remove $g $lno.0 "$lno.0 lineend + 1c"
+					}
+				}
+
+				foreach t [list \
+					$w_commit \
+					$w_author \
+					$w_date \
+					$w_filename \
+					$w_olno] {
+					$t delete $lno.0 "$lno.0 lineend"
+				}
 
 				$w_commit insert $lno.0 $abbrev
 				$w_author insert $lno.0 $author
@@ -3411,7 +3451,12 @@ proc read_blame_incremental {fd w
 				$w_filename insert $lno.0 $file
 				$w_olno insert $lno.0 $ol linenumber
 
-				set blame_data($w,line$lno,commit) $commit
+				set g g$cmit
+				foreach t $all {
+					$t tag add $g $lno.0 "$lno.0 lineend + 1c"
+				}
+
+				set blame_data($w,line$lno,commit) $cmit
 
 				incr n -1
 				incr lno