##
## view.nas
##
##  Nasal code for implementing view-specific functionality.



# Dynamically calculate limits so that it takes STEPS iterations to
# traverse the whole range, the maximum FOV is fixed at 120 degrees,
# and the minimum corresponds to normal maximum human visual acuity
# (~1 arc minute of resolution, although apparently people vary widely
# in this ability).  Quick derivation of the math:
#
#   mul^steps = max/min
#   steps * ln(mul) = ln(max/min)
#   mul = exp(ln(max/min) / steps)
STEPS = 40;
ACUITY = 1/60; # Maximum angle subtended by one pixel (== 1 arc minute)
max = min = mul = 0;
calcMul = func {
    max = 120; # Fixed at 120 degrees
    min = getprop("/sim/startup/xsize") * ACUITY;
    mul = math.exp(math.ln(max/min) / STEPS);
}

##
# Handler.  Increase FOV by one step
#
increase = func {
    calcMul();
    val = fovProp.getValue() * mul;
    if(val == max) { return; }
    if(val > max) { val = max }
    fovProp.setDoubleValue(val);
    gui.popupTip(sprintf("FOV: %.1f", val));
}

##
# Handler.  Decrease FOV by one step
#
decrease = func {
    calcMul();
    val = fovProp.getValue() / mul;
    fovProp.setDoubleValue(val);
    gui.popupTip(sprintf("FOV: %.1f%s", val, val < min ? " (overzoom)" : ""));
}

##
# Handler.  Reset FOV to default.
#
var resetFOV = func {
    setprop("/sim/current-view/field-of-view",
            getprop("/sim/current-view/config/default-field-of-view-deg"));
}

var resetViewPos = func {
    var n = getprop("/sim/current-view/view-number");
    var v = views[n].getNode("config");
    setprop("/sim/current-view/x-offset-m", v.getNode("x-offset-m", 1).getValue() or 0);
    setprop("/sim/current-view/y-offset-m", v.getNode("y-offset-m", 1).getValue() or 0);
    setprop("/sim/current-view/z-offset-m", v.getNode("z-offset-m", 1).getValue() or 0);
}

var resetViewDir = func {
    setprop("/sim/current-view/goal-heading-offset-deg",
            getprop("/sim/current-view/config/heading-offset-deg"));
    setprop("/sim/current-view/goal-pitch-offset-deg",
            getprop("/sim/current-view/config/pitch-offset-deg"));
    setprop("/sim/current-view/goal-roll-offset-deg",
            getprop("/sim/current-view/config/roll-offset-deg"));
}

##
# Handler.  Reset view to default.
#
resetView = func {
    if (getprop("/sim/current-view/view-number") == 6)
        return flyby.setpos(1);

    resetViewDir();
    resetFOV();
}

##
# Handler.  Step to the next view.
#
var stepView = func(n) {
    var i = getprop("/sim/current-view/view-number") + n;
    if (i < 0)
        i = size(views) - 1;
    elsif (i >= size(views))
        i = 0;
    setprop("/sim/current-view/view-number", i);

    # And pop up a nice reminder
    gui.popupTip(views[i].getNode("name").getValue());
}

##
# Standard view "slew" rate, in degrees/sec.
#
VIEW_PAN_RATE = 60;

##
# Pans the view horizontally.  The argument specifies a relative rate
# (or number of "steps" -- same thing) to the standard rate.
#
panViewDir = func(step) {
    if (getprop("/sim/freeze/master"))
        prop = "/sim/current-view/heading-offset-deg";
    else
        prop = "/sim/current-view/goal-heading-offset-deg";

    controls.slewProp(prop, step * VIEW_PAN_RATE);
}

##
# Pans the view vertically.  The argument specifies a relative rate
# (or number of "steps" -- same thing) to the standard rate.
#
panViewPitch = func(step) {
    if (getprop("/sim/freeze/master"))
        prop = "/sim/current-view/pitch-offset-deg";
    else
        prop = "/sim/current-view/goal-pitch-offset-deg";

    controls.slewProp(prop, step * VIEW_PAN_RATE);
}



##
# Singleton class that manages "Fly-By View". It's started with flyby.init()
# and then works autonomously.
#
var flyby = {
    init : func {
        me.latN = props.globals.getNode("/sim/viewer/latitude-deg", 1);
        me.lonN = props.globals.getNode("/sim/viewer/longitude-deg", 1);
        me.altN = props.globals.getNode("/sim/viewer/altitude-ft", 1);
        me.hdgN = props.globals.getNode("/orientation/heading-deg", 1);
        me.loopid = 0;
        me.number = nil;
        me.currview = nil;
        forindex (var i; views)
            if ((var v = views[i].getNode("name")) != nil and v.getValue() == "Fly-By View")
                me.number = i;
        if (me.number == nil)
            die("can't find 'Fly-By View'");

        setlistener("/sim/signals/reinit", func { cmdarg().getValue() or me.reset() });
        setlistener("/sim/crashed", func { cmdarg().getValue() and me.reset() });
        setlistener("/sim/freeze/replay-state", func {
            settimer(func { me.reset() }, 1); # time for replay to catch up
        });
        setlistener("/sim/current-view/view-number", func {
            me.currview = cmdarg().getValue();
            me.reset();
        }, 1);
    },
    reset: func {
        me.loopid += 1;
        me.currview == me.number or return;
        me.chase = -getprop("/sim/chase-distance-m");
        me.course = me.hdgN.getValue();
        me.last = geo.aircraft_position();
        me.setpos(1);
        me.dist = 20;
        me._loop_(me.loopid);
    },
    setpos : func(force = 0) {
        var pos = geo.aircraft_position();

        # check if the aircraft has moved enough
        var dist = me.last.distance_to(pos);
        if (dist < 1.7 * me.chase and !force)
            return 1.13;

        # "predict" and remember next aircraft position
        var course = me.hdgN.getValue();
        var delta_alt = (pos.alt() - me.last.alt()) * 0.5;
        pos.apply_course_distance(course, dist * 0.8);
        pos.set_alt(pos.alt() + delta_alt);
        me.last.set(pos);

        # apply random deviation
        var radius = me.chase * (0.5 * rand() + 0.7);
        var agl = getprop("/position/altitude-agl-ft") * geo.FT2M;
        if (agl > me.chase)
            var angle = rand() * 2 * math.pi;
        else
            var angle = ((2 * rand() - 1) * 0.15 + 0.5) * (rand() < 0.5 ? -math.pi : math.pi);

        var dev_alt = math.cos(angle) * radius;
        var dev_side = math.sin(angle) * radius;
        pos.apply_course_distance(course + 90, dev_side);

        # and make sure it's not under ground
        var lat = pos.lat();
        var lon = pos.lon();
        var alt = pos.alt();
        var elev = geo.elevation(lat, lon);
        if (elev != nil) {
            elev += 2;   # min elevation
            if (alt + dev_alt < elev and dev_alt < 0)
                dev_alt = -dev_alt;
            if (alt + dev_alt < elev)
                alt = elev;
            else
                alt += dev_alt;
        }

        # set new view point
        me.latN.setValue(lat);
        me.lonN.setValue(lon);
        me.altN.setValue(alt * geo.M2FT);
        return 6.3;
    },
    _loop_ : func(id) {
        id == me.loopid or return;
        settimer(func { me._loop_(id) }, me.setpos());
    },
};



#-- view manager --------------------------------------------------------------
#
# Saves/restores/moves the view point (position, orientation, field-of-view).
# Moves are interpolated with sinusoidal characteristic. There's only one
# instance of this class, available as "view.point".
#
# Usage:
#    view.point.save();        ... save current view and return reference to
#                                  saved values in the form of a props.Node
#
#    view.point.restore();     ... restore saved view parameters
#
#    view.point.move(<prop> [, <time>]);
#                              ... set view parameters from a props.Node with
#                                  optional move time in seconds. <prop> may be
#                                  nil, in which case nothing happens.
#
# A parameter set as expected by set() and returned by save() is a props.Node
# object containing any (or none) of these children:
#
#   <heading-offset-deg>
#   <pitch-offset-deg>
#   <roll-offset-deg>
#   <x-offset-m>
#   <y-offset-m>
#   <z-offset-m>
#   <field-of-view>
#   <move-time-sec>
#
# The <move-time> isn't really a property of the view, but is available
# for convenience. The time argument in the move() method overrides it.


##
# Normalize angle to  -180 <= angle < 180
#
var normdeg = func(a) {
    while (a >= 180) {
        a -= 360;
    }
    while (a < -180) {
        a += 360;
    }
    return a;
}


##
# Manages one translation/rotation axis. (For simplicity reasons the
# field-of-view parameter is also managed by this class.)
#
var ViewAxis = {
    new : func(prop) {
        var m = { parents : [ViewAxis] };
        m.prop = props.globals.getNode(prop, 1);
        if (m.prop.getType() == "NONE") {
            m.prop.setDoubleValue(0);
        }
        m.from = m.to = m.prop.getValue();
        return m;
    },
    reset : func {
        me.from = me.to = normdeg(me.prop.getValue());
    },
    target : func(v) {
        me.to = normdeg(v);
    },
    move : func(blend) {
        me.prop.setValue(me.from + blend * (me.to - me.from));
    },
};



##
# view.point: handles smooth view movements
#
var point = {
    init : func {
        me.axes = {
            "heading-offset-deg" : ViewAxis.new("/sim/current-view/goal-heading-offset-deg"),
            "pitch-offset-deg" : ViewAxis.new("/sim/current-view/goal-pitch-offset-deg"),
            "roll-offset-deg" : ViewAxis.new("/sim/current-view/goal-roll-offset-deg"),
            "x-offset-m" : ViewAxis.new("/sim/current-view/x-offset-m"),
            "y-offset-m" : ViewAxis.new("/sim/current-view/y-offset-m"),
            "z-offset-m" : ViewAxis.new("/sim/current-view/z-offset-m"),
            "field-of-view" : ViewAxis.new("/sim/current-view/field-of-view"),
        };
        me.storeN = props.Node.new();
        me.dtN = props.globals.getNode("/sim/time/delta-realtime-sec", 1);
        me.currviewN = props.globals.getNode("/sim/current-view", 1);
        me.blend = 0;
        me.loop_id = 0;
        props.copy(props.globals.getNode("/sim/view/config"), me.storeN);
    },
    save : func {
        me.storeN = props.Node.new();
        props.copy(me.currviewN, me.storeN);
        return me.storeN;
    },
    restore : func {
        me.move(me.storeN);
    },
    move : func(prop, time = nil) {
        prop != nil or return;
        foreach (var a; keys(me.axes)) {
            var n = prop.getNode(a);
            me.axes[a].reset();
            if (n != nil) {
                me.axes[a].target(n.getValue());
            }
        }
        var m = prop.getNode("move-time-sec");
        if (m != nil) {
            time = m.getValue();
        }
        if (time == nil) {
            time = 1;
        }
        me.blend = -1;   # range -1 .. 1
        me._loop_(me.loop_id += 1, time);
    },
    _loop_ : func(id, time) {
        me.loop_id == id or return;
        me.blend += me.dtN.getValue() / time;
        if (me.blend > 1) {
            me.blend = 1;
        }
        var b = (math.sin(me.blend * math.pi / 2) + 1) / 2; # range 0 .. 1
        foreach (var a; keys(me.axes)) {
            me.axes[a].move(b);
        }
        if (me.blend < 1) {
            settimer(func { me._loop_(id, time) }, 0);
        }
    },
};



var views = nil;
var fovProp = nil;


_setlistener("/sim/signals/nasal-dir-initialized", func {
    views = props.globals.getNode("/sim").getChildren("view");
    fovProp = props.globals.getNode("/sim/current-view/field-of-view");
    point.init();
});


_setlistener("/sim/signals/fdm-initialized", func {
    flyby.init();
});