const Tension := 1.3
const Length := 50
const maxspeed := 10
const gravity := 0.7
const loss := 1.1

function Angle (x1, y1, x2, y2 : real) : real
    var theta : real
    if x1 = x2 then
        if y2 > y1 then
            theta := 90
        else
            theta := 270
        end if
    else
        theta := arctand ((y1 - y2) / (x1 - x2))
        if x2 > x1 then
            if y2 > y1 then
            else
                theta := 360 + theta
            end if
        else
            theta := 180 + theta
        end if
    end if
    result theta
end Angle

function Dist (x1, y1, x2, y2 : real) : real
    result sqrt ((x2 - x1) ** 2 + (y2 - y1) ** 2)
end Dist


var mx, my, button : int
var x, y, xs, ys : real := 0
x := 100
y := 100

var keys : array char of boolean

View.Set ('offscreenonly')

loop

    mousewhere (mx, my, button)
    Input.KeyDown (keys)

    x += xs
    y += ys

    if keys ('d') then
        xs += 1
    elsif keys ('a') then
        xs -= 1
    end if

    if keys ('s') then
        ys -= 1
    elsif keys ('w') then
        ys += gravity * 0.9
    end if

    ys -= gravity

    drawline (mx, my, round (x), round (y), black)
    drawfilloval (round (x), round (y), 5, 5, black)

    xs /= loss
    ys /= loss

    if Dist (x, y, mx, my) > Length then
        xs += cosd (Angle (x, y, mx, my)) * Tension * Dist (x, y, mx, my) / Length
        ys += sind (Angle (x, y, mx, my)) * Tension * Dist (x, y, mx, my) / Length
    end if
    View.Update
    Time.DelaySinceLast (30)
    cls
end loop