git-gui: Use three colors for the blame viewer background

To prevent neighboring lines that are different commits from using
the same background color we now use 3 colors and assign them
by selecting the color that is not used before or after the line
in question.  We still color "on the fly" as we receive hunks from
git-blame, but we delay our color decisions until we are getting
the original location data (the slower -M -C -C pass) as that is
usually more fine-grained than the current location data.

Credit goes to Martin Waitz for the tri-coloring concept.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

lib/blame.tcl

@@ -26,8 +26,8 @@ field old_height ; # last known height of $w.file_pane
 
 # Tk UI colors
 #
-field active_color #c0edc5
-field group_colors {
+variable active_color #c0edc5
+variable group_colors {
 	#d6d6d6
 	#e1e1e1
 	#ececec
@@ -42,11 +42,9 @@ field current_fd        {} ; # background process running
 field highlight_line    -1 ; # current line selected
 field highlight_column  {} ; # current commit column selected
 field highlight_commit  {} ; # sha1 of commit selected
-field old_bgcolor       {} ; # background of current selection
 
 field total_lines       0  ; # total length of file
 field blame_lines       0  ; # number of lines computed
-field have_commit          ; # array commit -> 1
 field amov_data            ; # list of {commit origfile origline}
 field asim_data            ; # list of {commit origfile origline}
 
@@ -62,6 +60,8 @@ field tooltip_commit    {} ; # Commit(s) in tooltip
 
 constructor new {i_commit i_path} {
 	global cursor_ptr
+	variable active_color
+	variable group_colors
 
 	set commit $i_commit
 	set path   $i_path
@@ -250,6 +250,10 @@ constructor new {i_commit i_path} {
 		-command [cb _copycommit]
 
 	foreach i $w_columns {
+		for {set g 0} {$g < [llength $group_colors]} {incr g} {
+			$i tag conf color$g -background [lindex $group_colors $g]
+		}
+
 		$i conf -cursor $cursor_ptr
 		$i conf -yscrollcommand [list many2scrollbar \
 			$w_columns yview $w.file_pane.out.sby]
@@ -314,6 +318,8 @@ constructor new {i_commit i_path} {
 }
 
 method _load {jump} {
+	variable group_colors
+
 	_hide_tooltip $this
 
 	if {$total_lines != 0 || $current_fd ne {}} {
@@ -325,8 +331,10 @@ method _load {jump} {
 		foreach i $w_columns {
 			$i conf -state normal
 			$i delete 0.0 end
-			foreach cmit [array names have_commit] {
-				$i tag delete g$cmit
+			foreach g [$i tag names] {
+				if {[regexp {^g[0-9a-f]{40}$} $g]} {
+					$i tag delete $g
+				}
 			}
 			$i conf -state disabled
 		}
@@ -339,7 +347,6 @@ method _load {jump} {
 		set highlight_column {}
 		set highlight_commit {}
 		set total_lines 0
-		array unset have_commit
 	}
 
 	if {[winfo exists $w.status.c]} {
@@ -494,6 +501,7 @@ method _exec_blame {cur_w cur_d options cur_s} {
 
 method _read_blame {fd cur_w cur_d cur_s} {
 	upvar #0 $cur_d line_data
+	variable group_colors
 
 	if {$fd ne $current_fd} {
 		catch {close $fd}
@@ -508,16 +516,6 @@ method _read_blame {fd cur_w cur_d cur_s} {
 			set r_orig_line  $original_line
 			set r_final_line $final_line
 			set r_line_count $line_count
-
-			if {[catch {set g $have_commit($cmit)}]} {
-				set bg [lindex $group_colors 0]
-				set group_colors [lrange $group_colors 1 end]
-				lappend group_colors $bg
-				foreach i $w_columns {
-					$i tag conf g$cmit -background $bg
-				}
-				set have_commit($cmit) 1
-			}
 		} elseif {[string match {filename *} $line]} {
 			set file [string range $line 9 end]
 			set n    $r_line_count
@@ -563,6 +561,30 @@ method _read_blame {fd cur_w cur_d cur_s} {
 				incr first_lno -1
 			}
 
+			set color {}
+			if {$first_lno < $lno} {
+				foreach g [$w_file tag names $first_lno.0] {
+					if {[regexp {^color[0-9]+$} $g]} {
+						set color $g
+						break
+					}
+				}
+			} else {
+				set i [lsort [concat \
+					[$w_file tag names "[expr {$first_lno - 1}].0"] \
+					[$w_file tag names "[expr {$lno + $n}].0"] \
+					]]
+				for {set g 0} {$g < [llength $group_colors]} {incr g} {
+					if {[lsearch -sorted -exact $i color$g] == -1} {
+						set color color$g
+						break
+					}
+				}
+			}
+			if {$color eq {}} {
+				set color color0
+			}
+
 			while {$n > 0} {
 				set lno_e "$lno.0 lineend + 1c"
 				if {[lindex $line_data $lno] ne {}} {
@@ -583,6 +605,14 @@ method _read_blame {fd cur_w cur_d cur_s} {
 				}
 
 				foreach i $w_columns {
+					if {$cur_w eq $w_amov} {
+						for {set g 0} \
+							{$g < [llength $group_colors]} \
+							{incr g} {
+							$i tag remove color$g $lno.0 $lno_e
+						}
+						$i tag add $color $lno.0 $lno_e
+					}
 					$i tag add g$cmit $lno.0 $lno_e
 				}
 
@@ -616,6 +646,18 @@ method _read_blame {fd cur_w cur_d cur_s} {
 				} else {
 					$cur_w insert $lno.0 { |}
 				}
+
+				if {$cur_w eq $w_amov} {
+					foreach i $w_columns {
+						for {set g 0} \
+							{$g < [llength $group_colors]} \
+							{incr g} {
+							$i tag remove color$g $lno.0 $lno_e
+						}
+						$i tag add $color $lno.0 $lno_e
+					}
+				}
+
 				incr lno
 			}
 
@@ -678,10 +720,11 @@ method _load_commit {cur_w cur_d pos} {
 
 method _showcommit {cur_w lno} {
 	global repo_config
+	variable active_color
 
 	if {$highlight_commit ne {}} {
 		foreach i $w_columns {
-			$i tag conf g$highlight_commit -background $old_bgcolor
+			$i tag conf g$highlight_commit -background {}
 			$i tag lower g$highlight_commit
 		}
 	}
@@ -704,7 +747,6 @@ method _showcommit {cur_w lno} {
 		set cmit [lindex $dat 0]
 		set file [lindex $dat 1]
 
-		set old_bgcolor [$w_file tag cget g$cmit -background]
 		foreach i $w_columns {
 			$i tag conf g$cmit -background $active_color
 			$i tag raise g$cmit