Compute the distance between two marks

Question

I came across a question, while writing some vimscript. I wanted to know the "distance in motion" between two marks in the buffer.

The interesting point of this can be to know how many time I have to exectue a vim motion to go from one mark to the other in order to calculate the number of moves between the two marks.

How would you proceed?

Answer 1

You could use this function to do what you want:

It takes 3 arguments:

• A normal mode command (which should move the cursor)
• The mark where to beginning the motions
• The destination mark

It will return the minimal number of motions required to reach or overstep the destination mark

It test several cases and stop the function if

• The direction of the motion (forward or backward) doesn't allow to reach the destionation mark
• The command given as first parameter doesn't move the cursor
• One of the mark is undefined
• The mark are in the same position (0 is returned)

Examples of calls would be:

:call CountMotions("fa", "a", "b")
:call CountMotions("w", "c", "b")
:call CountMotions("h", "c", "e")

Beware if the first parameter is a destructive command (dd for example) it will be executed at least once.

Here is the function:

fun! CountMotions(motion, mark1, mark2)
    " Save the cursor position
    let savedPosition = getpos('.')

    " Get position of the marks
    execute "let m1Position = getpos(\"'" . a:mark1 . "\")"
    execute "let m2Position = getpos(\"'" . a:mark2 . "\")"

    " If a mark is undefined stop the function
    if (m1Position[1] == 0 && m1Position[2] == 0)
        echo "'" . a:mark1 . " is not defined"
        return -1
    endif
    if (m2Position[1] == 0 && m2Position[2] == 0)
        echo "'" . a:mark2 . " is not defined"
        return -1
    endif

    " If the marks are not on the same buffer stop the function
    if m1Position[0] != m2Position[0]
        echo "The marks are not on the same buffer"
        return -1
    endif

    " Position the cursor on the first mark
    call setpos('.', m1Position)

    " Get the distance between the two marks
    let distance = sqrt( pow((m2Position[1]-m1Position[1]),2) + pow(( m2Position[2]-m1Position[2] ),2) )
    let previousDistance = distance + 1

    " If the marks are on the same chatacter stop the function
    if ( distance == 0 )
        echo "the marks are on the same character"
        return 0
    endif

    " Check which mark is the first one in the buffer
    let firstMark = a:mark1
    if (m1Position[1] > m2Position[1])
        let firstMark = a:mark2
    elseif (m1Position[1] == m2Position[1])
        if (m1Position[2] > m2Position[2])
            let firstMark = a:mark2
        endif
    endif

    " Check in which direction the motion goes
        let direction = "forward"
        " Execute one motion and increment the count
        execute "normal " . a:motion
        " Get the position after the motion
        let newPosition = getpos('.')
        " Reposition the cursor on the first mark
        call setpos('.', m1Position)
        if (m1Position == newPosition)
            echo "The motion doesn't move the cursor"
            return -1
        endif
        if (m1Position[1] > newPosition[1])
            let direction = "backward"
        elseif (m1Position[1] == newPosition[1])
            if (m1Position[2] > newPosition[2])
                let direction = "backward"
            endif
        endif

    " If the direction doesn't allows to reach the second mark stop the function
    if ( (firstMark == a:mark1 && direction == "backward") || (firstMark == a:mark2 && direction == "forward") )
        echo "wrong way, mark unreachable"
        return -1
    endif

    let countMotion = 0
    let previousPosition = []
    let continue = 1

    " Count the number of motions
    while continue == 1
        " Execute one motion and increment the count
        execute "normal " . a:motion
        let countMotion = countMotion + 1

        " Update position
        let m1Position = getpos('.')

        " Calculate the changes in the distance
        let previousDistance = distance
        let distance = sqrt( pow((m2Position[1] - m1Position[1]), 2) + pow((m2Position[2] - m1Position[2]), 2))

        "echo "[" . m1Position[1] . " " . m1Position[2] . "]" . "[" . m2Position[1] . " " . m2Position[2] . "]" . "distances " . string( distance ) . "  " . string( previousDistance )

        " Check if the loop should continue
        if (distance >= previousDistance)
            let continue = 0
        endif
    endwhile

    " restore cursor position
    call setpos('.', savedPosition)

    echo a:motion . " needed: " . countMotion
    return countMotion
endfunction