#
# data structures
#
length = 300;
center = ['x' = 200; 'y' = 250;];
radius = 2 * length / sqrt (12);
fractalangle = 0;
maxlevel = 2;
sizes = [
    'button' = [ 'x' = 100; 'y' = 40;  ];
    'canvas' = [ 'x' = 400; 'y' = 500; ];
    'view'   = [ 'x' = 400; 'y' = 600; ];
];
sq = function (x) {
    return x * x;
};
#
# create view and other widgets
#
init = function () {
    view = createwidget (-1, [
        'type' = 'view'; 'name' = 'fractal'; 'size' = sizes.view;
    ]);

    array1 = createwidget (view, [
        'type' = 'array'; 'borderwidth' = 1; 'mode' = 'vertical';
    ]);
    widgets[array1].resize = resize;

    array2 = createwidget (array1, [
        'type' = 'array'; 'borderwidth' = 1; 'mode' = 'horizontal';
    ]);
    widgets[array2].resize = resize;

    array3 = createwidget (array2, [
        'type' = 'array'; 'borderwidth' = 1; 'mode' = 'vertical';
    ]);
    widgets[array3].resize = resize;

    morebutton = createwidget (array3, [
        'type' = 'button'; 'text' = 'more';
    ]);
    widgets[morebutton].pressed = pressed;
    lessbutton = createwidget (array3, [
        'type' = 'button'; 'text' = 'less';
    ]);
    widgets[lessbutton].pressed = pressed;
    setwidgetattr (morebutton, ['size' = sizes.button;]);
    setwidgetattr (lessbutton, ['size' = sizes.button;]);

    atext = createwidget (array2, [
        'type' = 'text'; 'mode' = 'oneline';
    ]);
    widgets[atext].oneline = oneline;
    setwidgetattr (atext, [
        'size' = ['x' = sizes.button.x; 'y' = sizes.button.y * 2;];
    ]);

    scroll = createwidget (array1, ['type' = 'scroll';]);
    canvas = createwidget (scroll, ['type' = 'canvas';]);
    wrect = [0 = ['x' = 0; 'y' = 0;]; 1 = sizes.canvas;];
    setwidgetattr (canvas, ['window' = wrect; 'viewport' = wrect[1];]);
};
#
# drawing functions
#
# draw a Koch curve (a ``snowflake'' fractal)
#
# start with a triangle and keep replacing edges
# with the construct: _/\_
# until the recursion level reaches 'maxlevel'
#
fractal = function (level, length, angle) {
    local nlength, newpenpos;

    if (level >= maxlevel) {
        newpenpos.x = penpos.x + length * cos (angle);
        newpenpos.y = penpos.y + length * sin (angle);
        line (canvas, null, penpos, newpenpos, ['color' = 1;]);
        penpos = newpenpos;
        return;
    }
    nlength = length / 3;
    fractal (level + 1, nlength, angle);
    fractal (level + 1, nlength, angle + 60);
    fractal (level + 1, nlength, angle - 60);
    fractal (level + 1, nlength, angle);
};
redrawfractal = function () {
    clear (canvas);
    setpick (canvas, center, wrect);
    penpos = [
        'x' = center.x + cos (fractalangle + 210) * radius;
        'y' = center.y + sin (fractalangle + 210) * radius;
    ];
    fractal (0, length, fractalangle +  60);
    fractal (0, length, fractalangle -  60);
    fractal (0, length, fractalangle - 180);
    remove ('penpos');
};
#
# editing functions
#
# transform the fractal.
#
# map point 'prevpoint' to point 'currpoint'
# with respect to the center of the fractal.
#
transformfractal = function (prevpoint, currpoint) {
    local prevtan, currtan, prevradius, currradius;

    prevtan = atan (prevpoint.y - center.y, prevpoint.x - center.x);
    currtan = atan (currpoint.y - center.y, currpoint.x - center.x);
    fractalangle = fractalangle + (currtan - prevtan);
    prevradius = sqrt (
        sq (prevpoint.y - center.y) + sq (prevpoint.x - center.x)
    );
    currradius = sqrt (
        sq (currpoint.y - center.y) + sq (currpoint.x - center.x)
    );
    radius = radius / prevradius * currradius;
    length = radius / 2 * sqrt (12);
};
#
# main actions
#
redraw = function (data) {
    redrawfractal ();
};
changemaxlevel = function (dn) {
    maxlevel = maxlevel + dn;
    if (maxlevel < 0)
        maxlevel = 0;
    redrawfractal ();
};
resize = function (data) {
    local ret;
    if (data.widget == array1) {
        ret = [
            array2 = [
                'x' = data.size.x;
                'y' = sizes.button.y * 2;
            ];
            scroll = [
                'x' = data.size.x;
                'y' = data.size.y - sizes.button.y * 2;
            ];
        ];
    } else if (data.widget == array2) {
        ret = [
            array3 = [
                'x' = sizes.button.x;
                'y' = 2 * sizes.button.y;
            ];
            atext = [
                'x' = data.size.x - sizes.button.x;
                'y' = 2 * sizes.button.y;
            ];
        ];
    } else if (data.widget == array3) {
        ret = [
            morebutton = sizes.button;
            lessbutton = sizes.button;
        ];
    }
    return ret;
};
#
# user interface functions
#
# bind changes to the fractal to user actions
#
leftup = function (data) {
    transformfractal (data.ppos, data.pos);
    redrawfractal ();
};
menu = [
    0 = 'more';
    1 = 'less';
];
domenu = function (i) {
    local s;
    s = menu[i];
    if (s == 'more')
        changemaxlevel (1);
    else if (s == 'less')
        changemaxlevel (-1);
};
rightdown = function (data) {
    domenu (displaymenu (canvas, menu));
};
pressed = function (data) {
    if (data.widget == morebutton)
        changemaxlevel (1);
    else if (data.widget == lessbutton)
        changemaxlevel (-1);
};
oneline = function (data) {
    local dn;
    dn = ston (data.text);
    if (dn > 0 | dn < 0)
        changemaxlevel (dn - maxlevel);
};
#
# postscript generation
#
dops = function () {
    local r;

    r = [0 = ['x' = 0; 'y' = 0;]; 1 = ['x' = 8 * 300; 'y' = 10.5 * 300;];];
    canvas = opencanvas ('pscanvas', '', r);
    setwidgetattr (canvas, ['window' = wrect;]);
    redraw ();
    closecanvas (canvas);
    canvas=defcanvas;
};
init ();
#txtview ('off');