Eskil

        for {set t 0} {$t < $n2} {incr t} {
            gets $ch2 apa
            append data2 $apa\n
            incr doingLine2
        }
        lappend diff($top,leftMergeData) $data1
        lappend diff($top,rightMergeData) $data2
        set diff($top,mergeSelection,$changeNo) \
                [WhichSide $top $line1 $n1 $line2 $n2]
        incr changeNo
    }
    set data1 {}
    set data2 {}
    while {[gets $ch1 apa] != -1} {
        append data1 $apa\n
        incr doingLine1

    set t 0
    foreach {commLeft diffLeft} $diff($top,leftMergeData) \
            {commRight diffRight} $diff($top,rightMergeData) {
        $w insert end $commRight
        if {![info exists diff($top,mergeSelection,$t)]} continue
        $w mark set merges$t insert
        $w mark gravity merges$t left
        switch $diff($top,mergeSelection,$t) {
            1 { $w insert end $diffLeft merge$t }
            2 { $w insert end $diffRight merge$t }
            12 { $w insert end $diffLeft merge$t 
                $w insert end $diffRight merge$t }
            21 { $w insert end $diffRight merge$t
                $w insert end $diffLeft merge$t  }
        }
        lappend marks mergee$t [$w index insert]

        incr t
    }
    foreach {mark index} $marks {
        $w mark set $mark $index
    }
    # Add fences to simplify some handling later
    $w mark set mergee-2 1.0
    $w mark set mergee-1 1.0
    $w mark set merges$t end
    $w mark set merges[expr {$t + 1}] end

    set diff($top,curMerge) 0
    set diff($top,curMergeSel) $diff($top,mergeSelection,0)
    $w tag configure merge0 -foreground red
    showDiff $top 0
    update
    # If there is any diff, show the first
    if {$t > 0} {
        seeText $w merges0 mergee0
    }

    collectMergeData $top
    fillMergeWindow $top
}

# Compare each file agains an ancestor file for three-way merge
proc collectAncestorInfo {top dFile1 dFile2 opts} {
    array unset ::diff $top,ancestorLeft,*
    array unset ::diff $top,ancestorRight,*
    set differrA1 [catch {DiffUtil::diffFiles {*}$opts \
            $::diff($top,ancestorFile) $dFile1} diffresA1]
    set differrA2 [catch {DiffUtil::diffFiles {*}$opts \
            $::diff($top,ancestorFile) $dFile2} diffresA2]
    if {$differrA1 != 0 || $differrA2 != 0} {
        puts $diffresA1
        puts $diffresA2
        return
    }
    foreach i $diffresA1 {
        lassign $i line1 n1 line2 n2
        if {$n1 == 0} {
            # Added lines
            for {set t $line2} {$t < $line2 + $n2} {incr t} {
                set ::diff($top,ancestorLeft,$t) a
            }
        } elseif {$n2 == 0} {
            # Deleted lines
            # Mark the following line
            set ::diff($top,ancestorLeft,d$line2) d
        } else {
            # Changed lines
            for {set t $line2} {$t < $line2 + $n2} {incr t} {
                set ::diff($top,ancestorLeft,$t) c
            }
        }
    }            
    foreach i $diffresA2 {
        lassign $i line1 n1 line2 n2
        if {$n1 == 0} {
            # Added lines
            for {set t $line2} {$t < $line2 + $n2} {incr t} {
                set ::diff($top,ancestorRight,$t) a
            }
        } elseif {$n2 == 0} {
            # Deleted lines
            # Mark the following line
            set ::diff($top,ancestorRight,d$line2) d
        } else {
            # Changed lines
            for {set t $line2} {$t < $line2 + $n2} {incr t} {
                set ::diff($top,ancestorRight,$t) c
            }
        }
    }
    #parray ::diff $top,ancestor*
}

# Use ancestor info to select which side to use in a merge chunk
proc WhichSide {top line1 n1 line2 n2} {
    if {$n1 == 0} {
        # Only to the right, this can be:
        set delLeft [info exists ::diff($top,ancestorLeft,d$line1)]
        # Inserted to right : Keep right side
        if {!$delLeft} { return 2 }

        for {set t $line2} {$t < $line2 + $n2} {incr t} {
            if {[info exists ::diff($top,ancestorRight,$t)]} {
                set right($::diff($top,ancestorRight,$t)) 1
            }
        }
        # Deleted to left   : Keep left side
        if {[array size right] == 0} { return 1 }
        # Deleted to left and changed to the right : ?? (right for now)
        # FIXA
        return 2
    } elseif {$n2 == 0} {
        # Only to the left, this can be:
        set delRight [info exists ::diff($top,ancestorRight,d$line2)]
        # Inserted to left : Keep left side
        if {!$delRight} { return 1 }

        for {set t $line1} {$t < $line1 + $n1} {incr t} {
            if {[info exists ::diff($top,ancestorLeft,$t)]} {
                set left($::diff($top,ancestorLeft,$t)) 1
            }
        }
        # Deleted to right : Keep right side
        if {[array size left] == 0} { return 2 }
        # Deleted to right and changed to the left : ?? (left for now)
        # FIXA
        return 1
    } else {
        # Changed on both sides, this can be:
        for {set t $line1} {$t < $line1 + $n1} {incr t} {
            if {[info exists ::diff($top,ancestorLeft,$t)]} {
                set left($::diff($top,ancestorLeft,$t)) 1
            }
        }
        # Changed to the right : Keep right
        if {[array size left] == 0} { return 2 }

        for {set t $line2} {$t < $line2 + $n2} {incr t} {
            if {[info exists ::diff($top,ancestorRight,$t)]} {
                set right($::diff($top,ancestorRight,$t)) 1
            }
        }

        # Changed to the left : Keep left
        if {[array size right] == 0} { return 1 }

        # Changed in both, right for now
        # FIXA
        return 2
    }
}