Extending turtle graphics ( vector files)

Purpose

Turtle graphics are a perhaps neglected use of JB/LB. They chime with students from a very early age, since they can relate to 'going forward' and 'turning'. They love patterns like 'squirals' of near-90 degree turns and changing length...

What I did was design a format for a descriptor-string which specifies shapes as a series of 'forwards' and 'turns'. To draw a square you go forward four equal distances, turning 90 degrees after each move. This I save as '4, 1, 90, 1, 90, 1, 90, 1, 90'. The initial 4 means there are four nodes defined by distance to reach them and angle to then turn..

This works nicely- a very simple LB program can read such a string and parse out the moves and turns. By writting it into a little rooutine you can call it with the shape$ specified, to start at a desired screen position, and initial orientation, width of line and colour, and draw the shape, to scale. Then I realised that for more interesting shapes it woukld be stupid to draw a shape on paper and measure the distances/angles by hand. So instead I mouse-click the shape as a sries of positions on a window and derive the values from the mouse x/y coordinates. It's all a work-in-progress. There are various bits yet to implement or a bit ugly at present. I may add a marker for 'pen up' and 'pen down' to allow discontinuous shapes. Or many other ideas. And I'll be tidying up a lot before completing this webpage with a link to source LB code. But it already allows me to save any interesting shapes in a shape-library. And you can contribute your own!

Some simple shapes

Pentangle

10,  
1,    144,     1,    144,     1,     144,    1,   144,    1,  144,   1,   144

Dancer

70,          
0.10,  49.09,  0.26, -40.17,  0.14,  47.40,  0.20, -76.53,  0.32, -25.40,  0.18,  48.90,  0.04,  
72.69,  0.13, 101.83,  0.24, -50.45,  0.10, -63.91,  0.13, -54.34,  0.15,  18.32,  0.12,  67.36,  0.11,  
51.55,  0.08,  83.88,  0.09,  20.37,  0.07, -31.27,  0.06, -74.28,  0.09, -32.63,  0.19, -44.18,  0.32,  
41.09,  0.03, 122.05,  0.23,-310.27,  0.22, 332.11,  0.18, -39.49,  0.17, -70.22,  0.27,  
42.99,  0.09, -33.02,  0.14,-214.99,  0.25,  64.99,  0.06, -64.82,  0.15, 308.19,  0.21, -56.02,  
0.17,  41.34,  0.03,-232.13

Simple LB code calling a defined shape twice.

'   NB turtle commands work in  DEGREES....

    nomainwin
    WindowWidth  =830:     WindowHeight =650
    graphicbox #w.gb, 10, 10, 800, 600

    open "Display" for window as #w

    #w "trapclose [quit]"

    shape$ ="10,  1,    144,     1,    144,     1,     144,    1,   144,    1,  144,   1,   144"    '   pentangle

    #w.gb "home ; down ; fill 60 60 60"

    radius =240: side =20

    call display shape$, 100, " 50 255 120", 500, 300,  0 '   here, a single call. Easily repeatedly called by program.
    call display shape$,  60, "255  50 120", 500, 400, 20

    wait

  [quit]
    close #w
    end

    sub display shape$, scale, col$, x, y, angle
        noOfTerms =val( word$( shape$, 1, ","))
        #w.gb "color "; col$
        #w.gb "up ; goto "; x; " "; y; " ; down ; size 1"
        #w.gb "north ; turn "; angle
        for i =1 to noOfTerms step 2
            vStep  =val( word$( shape$, i +1,    ","))
            vAngle =val( word$( shape$, i +2, ","))
            #w.gb "go ";    vStep *scale
            #w.gb "turn ";  vAngle
            print "go "; vStep *100; " ; turn "; vAngle
        next i
    end sub

To be continued...