flightgear/src/Instrumentation/HUD/HUD_ladder.cxx

// HUD_ladder.cxx -- HUD Ladder Instrument
//
// Written by Michele America, started September 1997.
//
// Copyright (C) 1997  Michele F. America  [micheleamerica#geocities:com]
// Copyright (C) 2006  Melchior FRANZ  [mfranz#aon:at]
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <simgear/math/vector.hxx>
#include <Main/viewer.hxx>
#include "HUD.hxx"


// FIXME
float get__heading() { return fgGetFloat("/orientation/heading-deg") * M_PI / 180.0; }
float get__throttleval() { return fgGetFloat("/controls/engines/engine/throttle"); }
float get__Vx() { return fgGetFloat("/velocities/uBody-fps"); }
float get__Vy() { return fgGetFloat("/velocities/vBody-fps"); }
float get__Vz() { return fgGetFloat("/velocities/wBody-fps"); }
float get__Ax() { return fgGetFloat("/acclerations/pilot/x-accel-fps_sec"); }
float get__Ay() { return fgGetFloat("/acclerations/pilot/y-accel-fps_sec"); }
float get__Az() { return fgGetFloat("/acclerations/pilot/z-accel-fps_sec"); }
float get__alpha() { return fgGetFloat("/orientation/alpha-deg"); }
float get__beta() { return fgGetFloat("/orientation/side-slip-deg"); }
#undef ENABLE_SP_FDM


HUD::Ladder::Ladder(HUD *hud, const SGPropertyNode *n, float x, float y) :
    Item(hud, n, x, y),
    _pitch(n->getNode("pitch-input", false)),
    _roll(n->getNode("roll-input", false)),
    _width_units(int(n->getFloatValue("display-span"))),
    _div_units(int(fabs(n->getFloatValue("divisions")))),
    _scr_hole(n->getIntValue("screen-hole")),
    _compression(n->getFloatValue("compression-factor")),
    _dynamic_origin(n->getBoolValue("enable-dynamic-origin")),
    _clip_plane(n->getBoolValue("enable-clip-plane")),
    _frl(n->getBoolValue("enable-fuselage-ref-line")),
    _target_spot(n->getBoolValue("enable-target-spot")),
    _target_markers(n->getBoolValue("enable-target-markers")),
    _velocity_vector(n->getBoolValue("enable-velocity-vector")),
    _drift_marker(n->getBoolValue("enable-drift-marker")),
    _alpha_bracket(n->getBoolValue("enable-alpha-bracket")),
    _energy_marker(n->getBoolValue("enable-energy-marker")),
    _climb_dive_marker(n->getBoolValue("enable-climb-dive-marker")),
    _glide_slope_marker(n->getBoolValue("enable-glide-slope-marker")),
    _glide_slope(n->getFloatValue("glide-slope", -4.0)),
    _energy_worm(n->getBoolValue("enable-energy-marker")),
    _waypoint_marker(n->getBoolValue("enable-waypoint-marker")),
    _zenith(n->getBoolValue("enable-zenith")),
    _nadir(n->getBoolValue("enable-nadir")),
    _hat(n->getBoolValue("enable-hat"))
{
    const char *t = n->getStringValue("type");
    _type = strcmp(t, "climb-dive") ? PITCH : CLIMB_DIVE;

    if (!_width_units)
        _width_units = 45;

    _vmax = _width_units / 2;
    _vmin = -_vmax;
}


void HUD::Ladder::draw(void)
{
    if (!_pitch.isValid() || !_roll.isValid())
        return;

    float roll_value = _roll.getFloatValue() * SGD_DEGREES_TO_RADIANS;
    float pitch_value = _pitch.getFloatValue();
    float alpha;

    //**************************************************************
    glPushMatrix();
    glTranslatef(_center_x, _center_y, 0);

    // OBJECT STATIC RETICLE
    // TYPE FRL (FUSELAGE REFERENCE LINE)
    // ATTRIB - ALWAYS
    // Draw the FRL spot and line
    if (_frl) {
#define FRL_DIAMOND_SIZE 2.0
        glBegin(GL_LINE_LOOP);
        glVertex2f(-FRL_DIAMOND_SIZE, 0.0);
        glVertex2f(0.0, FRL_DIAMOND_SIZE);
        glVertex2f(FRL_DIAMOND_SIZE, 0.0);
        glVertex2f(0.0, -FRL_DIAMOND_SIZE);
        glEnd();

        glBegin(GL_LINE_STRIP);
        glVertex2f(0, FRL_DIAMOND_SIZE);
        glVertex2f(0, 8.0);
        glEnd();
#undef FRL_DIAMOND_SIZE
    }
    // TYPE WATERLINE_MARK (W shaped _    _ )		// TODO (-> HUD_misc.cxx)
    //                                \/\/

    //****************************************************************
    // TYPE TARGET_SPOT
    // Draw the target spot.
    if (_target_spot) {
#define CENTER_DIAMOND_SIZE 6.0
        glBegin(GL_LINE_LOOP);
        glVertex2f(-CENTER_DIAMOND_SIZE, 0.0);
        glVertex2f(0.0, CENTER_DIAMOND_SIZE);
        glVertex2f(CENTER_DIAMOND_SIZE, 0.0);
        glVertex2f(0.0, -CENTER_DIAMOND_SIZE);
        glEnd();
#undef CENTER_DIAMOND_SIZE
    }

    //****************************************************************
    //velocity vector reticle - computations
    float xvvr, /* yvvr, */ Vxx = 0.0, Vyy = 0.0, Vzz = 0.0;
    float Axx = 0.0, Ayy = 0.0, Azz = 0.0, total_vel = 0.0, pot_slope, t1;
    float up_vel, ground_vel, actslope = 0.0, psi = 0.0;
    float vel_x = 0.0, vel_y = 0.0, drift;

    if (_velocity_vector) {
        drift = get__beta();
        alpha = get__alpha();

        Vxx = get__Vx();
        Vyy = get__Vy();
        Vzz = get__Vz();
        Axx = get__Ax();
        Ayy = get__Ay();
        Azz = get__Az();
        psi = get__heading();

        if (psi > 180.0)
            psi = psi - 360;

        total_vel = sqrt(Vxx * Vxx + Vyy * Vyy + Vzz * Vzz);
        ground_vel = sqrt(Vxx * Vxx + Vyy * Vyy);
        up_vel = Vzz;

        if (ground_vel < 2.0) {
            if (fabs(up_vel) < 2.0)
                actslope = 0.0;
            else
                actslope = (up_vel / fabs(up_vel)) * 90.0;

        } else {
            actslope = atan(up_vel / ground_vel) * SGD_RADIANS_TO_DEGREES;
        }

        xvvr = (-drift * (_compression / globals->get_current_view()->get_aspect_ratio()));
        // drift = ((atan2(Vyy, Vxx) * SGD_RADIANS_TO_DEGREES) - psi);
        // yvvr = (-alpha * _compression);
        // vel_y = (-alpha * cos(roll_value) + drift * sin(roll_value)) * _compression;
        // vel_x = (alpha * sin(roll_value) + drift * cos(roll_value))
        //         * (_compression / globals->get_current_view()->get_aspect_ratio());
        vel_y = -alpha * _compression;
        vel_x = -drift * (_compression / globals->get_current_view()->get_aspect_ratio());
        //  printf("%f %f %f %f\n",vel_x, vel_y, drift, psi);

        //****************************************************************
        // OBJECT MOVING RETICLE
        // TYPE - DRIFT MARKER
        // ATTRIB - ALWAYS
        // drift marker
        if (_drift_marker) {
            glBegin(GL_LINE_STRIP);
            glVertex2f((xvvr * 25 / 120) - 6, -4);
            glVertex2f(xvvr * 25 / 120, 8);
            glVertex2f((xvvr * 25 / 120) + 6, -4);
            glEnd();
        }

        //****************************************************************
        // Clipping coordinates for ladder to be input from xml file
        // Clip hud ladder.  FIXME, these should be configurable, but they
        // have always been hardcoded here.
        if (_clip_plane) {
            GLdouble eqn_top[4] = {0.0, -1.0, 0.0, 0.0};
            GLdouble eqn_left[4] = {-1.0, 0.0, 0.0, 100.0};
            GLdouble eqn_right[4] = {1.0, 0.0, 0.0, 100.0};

            glClipPlane(GL_CLIP_PLANE0, eqn_top);
            glEnable(GL_CLIP_PLANE0);
            glClipPlane(GL_CLIP_PLANE1, eqn_left);
            glEnable(GL_CLIP_PLANE1);
            glClipPlane(GL_CLIP_PLANE2, eqn_right);
            glEnable(GL_CLIP_PLANE2);
        }

        //****************************************************************
        // OBJECT MOVING RETICLE
        // TYPE VELOCITY VECTOR
        // ATTRIB - ALWAYS
        // velocity vector
        draw_circle(vel_x, vel_y, 6);

        //velocity vector reticle orientation lines
        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x - 12, vel_y);
        glVertex2f(vel_x - 6, vel_y);
        glEnd();
        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x + 12, vel_y);
        glVertex2f(vel_x + 6, vel_y);
        glEnd();
        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x, vel_y + 12);
        glVertex2f(vel_x, vel_y + 6);
        glEnd();

#ifdef ENABLE_SP_FDM
        int lgear = get__iaux3();
        int ihook = get__iaux6();

        // OBJECT MOVING RETICLE
        // TYPE LINE
        // ATTRIB - ON CONDITION
        if (lgear == 1) {
            // undercarriage status
            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x + 8, vel_y);
            glVertex2f(vel_x + 8, vel_y - 4);
            glEnd();

            // OBJECT MOVING RETICLE
            // TYPE LINE
            // ATTRIB - ON CONDITION
            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x - 8, vel_y);
            glVertex2f(vel_x - 8, vel_y - 4);
            glEnd();

            // OBJECT MOVING RETICLE
            // TYPE LINE
            // ATTRIB - ON CONDITION
            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x, vel_y - 6);
            glVertex2f(vel_x, vel_y - 10);
            glEnd();
        }

        // OBJECT MOVING RETICLE
        // TYPE V
        // ATTRIB - ON CONDITION
        if (ihook == 1) {
            // arrestor hook status
            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x - 4, vel_y - 8);
            glVertex2f(vel_x, vel_y - 10);
            glVertex2f(vel_x + 4, vel_y - 8);
            glEnd();
        }
#endif
    } // if _velocity_vector

    // draw hud markers on top of each AI/MP target
    if (_target_markers) {
        SGPropertyNode *models = globals->get_props()->getNode("/ai/models", true);
        for (int i = 0; i < models->nChildren(); i++) {
            SGPropertyNode *chld = models->getChild(i);
            string name;
            name = chld->getName();
            if (name == "aircraft" || name == "multiplayer") {
                string callsign = chld->getStringValue("callsign");
                if (callsign != "") {
                    float h_deg = chld->getFloatValue("radar/h-offset");
                    float v_deg = chld->getFloatValue("radar/v-offset");
                    float pos_x = (h_deg * cos(roll_value) -
                                   v_deg * sin(roll_value)) * _compression;
                    float pos_y = (v_deg * cos(roll_value) +
                                   h_deg * sin(roll_value)) * _compression;
                    draw_circle(pos_x, pos_y, 8);
                }
            }
        }
    }

    //***************************************************************
    // OBJECT MOVING RETICLE
    // TYPE - SQUARE_BRACKET
    // ATTRIB - ON CONDITION
    // alpha bracket
#ifdef ENABLE_SP_FDM
    alpha = get__alpha();

    if (_alpha_bracket && ihook == 1) {
        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x - 20, vel_y - (16 - alpha) * _compression);
        glVertex2f(vel_x - 17, vel_y - (16 - alpha) * _compression);
        glVertex2f(vel_x - 17, vel_y - (14 - alpha) * _compression);
        glVertex2f(vel_x - 20, vel_y - (14 - alpha) * _compression);
        glEnd();

        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x + 20, vel_y - (16 - alpha) * _compression);
        glVertex2f(vel_x + 17, vel_y - (16 - alpha) * _compression);
        glVertex2f(vel_x + 17, vel_y - (14 - alpha) * _compression);
        glVertex2f(vel_x + 20, vel_y - (14 - alpha) * _compression);
        glEnd();
    }
#endif
    //printf("xvr=%f, yvr=%f, Vx=%f, Vy=%f, Vz=%f\n",xvvr, yvvr, Vx, Vy, Vz);
    //printf("Ax=%f, Ay=%f, Az=%f\n",Ax, Ay, Az);

    //****************************************************************
    // OBJECT MOVING RETICLE
    // TYPE ENERGY_MARKERS
    // ATTRIB - ALWAYS
    //energy markers - compute potential slope
    float pla = get__throttleval();
    float t2 = 0.0;

    if (_energy_marker) {
        if (total_vel < 5.0) {
            t1 = 0;
            t2 = 0;
        } else {
            t1 = up_vel / total_vel;
            t2 = asin((Vxx * Axx + Vyy * Ayy + Vzz * Azz) / (9.81 * total_vel));
        }
        pot_slope = ((t2 / 3) * SGD_RADIANS_TO_DEGREES) * _compression + vel_y;
        // if (pot_slope < (vel_y - 45)) pot_slope = vel_y - 45;
        // if (pot_slope > (vel_y + 45)) pot_slope = vel_y + 45;

        //energy markers
        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x - 20, pot_slope - 5);
        glVertex2f(vel_x - 15, pot_slope);
        glVertex2f(vel_x - 20, pot_slope + 5);
        glEnd();

        glBegin(GL_LINE_STRIP);
        glVertex2f(vel_x + 20, pot_slope - 5);
        glVertex2f(vel_x + 15, pot_slope);
        glVertex2f(vel_x + 20, pot_slope + 5);
        glEnd();

        if (pla > (105.0 / 131.0)) {
            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x - 24, pot_slope - 5);
            glVertex2f(vel_x - 19, pot_slope);
            glVertex2f(vel_x - 24, pot_slope + 5);
            glEnd();

            glBegin(GL_LINE_STRIP);
            glVertex2f(vel_x + 24, pot_slope - 5);
            glVertex2f(vel_x + 19, pot_slope);
            glVertex2f(vel_x + 24, pot_slope + 5);
            glEnd();
        }
    }

    //**********************************************************
    // ramp reticle
    // OBJECT STATIC RETICLE
    // TYPE LINE
    // ATTRIB - ON CONDITION
#ifdef ENABLE_SP_FDM
    int ilcanclaw = get__iaux2();

    if (_energy_worm && ilcanclaw == 1) {
        glBegin(GL_LINE_STRIP);
        glVertex2f(-15, -134);
        glVertex2f(15, -134);
        glEnd();

        // OBJECT MOVING RETICLE
        // TYPE BOX
        // ATTRIB - ON CONDITION
        glBegin(GL_LINE_STRIP);
        glVertex2f(-6, -134);
        glVertex2f(-6, t2 * SGD_RADIANS_TO_DEGREES * 4.0 - 134);
        glVertex2f(+6, t2 * SGD_RADIANS_TO_DEGREES * 4.0 - 134);
        glVertex2f(6, -134);
        glEnd();

        // OBJECT MOVING RETICLE
        // TYPE DIAMOND
        // ATTRIB - ON CONDITION
        glBegin(GL_LINE_LOOP);
        glVertex2f(-6, actslope * 4.0 - 134);
        glVertex2f(0, actslope * 4.0 -134 + 3);
        glVertex2f(6, actslope * 4.0 - 134);
        glVertex2f(0, actslope * 4.0 -134 -3);
        glEnd();
    }
#endif

    //*************************************************************
    // OBJECT MOVING RETICLE
    // TYPE DIAMOND
    // ATTRIB - ALWAYS
    // Draw the locked velocity vector.
    if (_climb_dive_marker) {
        glBegin(GL_LINE_LOOP);
        glVertex2f(-3.0, 0.0 + vel_y);
        glVertex2f(0.0, 6.0 + vel_y);
        glVertex2f(3.0, 0.0 + vel_y);
        glVertex2f(0.0, -6.0 + vel_y);
        glEnd();
    }

    //****************************************************************

    if (_dynamic_origin) {
        // ladder moves with alpha/beta offset projected onto horizon
        // line (so that the horizon line always aligns with the
        // actual horizon.
        _vmin = pitch_value - _width_units * 0.5f;
        _vmax = pitch_value + _width_units * 0.5f;
        {
            // the hud ladder center point should move relative to alpha/beta
            // however the horizon line should always stay on the horizon.  We
            // project the alpha/beta offset onto the horizon line to get the
            // result we want.
            sgdVec3 p1; // result
            sgdVec3 p; sgdSetVec3(p, vel_x, vel_y, 0.0);
            sgdVec3 p0; sgdSetVec3(p0, 0.0, 0.0, 0.0);
            sgdVec3 d; sgdSetVec3(d, cos(roll_value), sin(roll_value), 0.0);
            sgdClosestPointToLine(p1, p, p0, d);
            glTranslatef(p1[0], p1[1], 0);
        }
    } else {
        // ladder position is fixed relative to the center of the screen.
        _vmin = pitch_value - _width_units * 0.5f;
        _vmax = pitch_value + _width_units * 0.5f;
    }

    glRotatef(roll_value * SGD_RADIANS_TO_DEGREES, 0.0, 0.0, 1.0);
    // FRL marker not rotated - this line shifted below
    float half_span = _w / 2.0;
    float y = 0, y_end = 0;
    float x_ini, x_ini2;
    float x_end, x_end2;

    if (_div_units) {
        const int BUFSIZE = 8;
        char buf[BUFSIZE];
        const float zero_offset = 50.0f; // horizon line is wider by this much

        _locTextList.setFont(_hud->_font_renderer);
        _locTextList.erase();
        _locLineList.erase();
        _locStippleLineList.erase();

        int last = int(_vmax) + 1;
        int i = int(_vmin);

        if (!_scr_hole) {
            x_end = half_span;

            for (; i < last; i++) {
                y = (i - pitch_value) * _compression + .5f;

                if (!(i % _div_units)) {           //  At integral multiple of div
                    snprintf(buf, BUFSIZE, "%d", i);
                    x_ini = -half_span;

                    if (i == 0) {
                        // Make zero point wider on left
                        x_ini -= zero_offset;
                        x_end += zero_offset;

                        draw_line(x_ini, y, x_end, y);

                    } else if (i > 0) {
                        // Zero or above draw solid lines
                        draw_line(x_ini, y, x_end, y);

                        if (i == 90 && _zenith)
                            draw_zenith(0.0, y);
                    } else {
                        // Below zero draw dashed lines.
                        draw_stipple_line(x_ini, y, x_end, y);

                        if (i == -90 && _nadir)
                            draw_nadir(0.0, y);
                    }

                    draw_text(x_ini - 4, y, buf, HUDText::VCENTER|HUDText::LEFT);
                    draw_text(x_end + 4, y, buf, HUDText::VCENTER|HUDText::RIGHT);
                }
            }

        } else { // if (_scr_hole)
            // Draw ladder with space in the middle of the lines
            float hole = _scr_hole / 2.0f;

            x_end = -half_span + hole;
            x_ini2 = half_span - hole;

            for (; i < last; i++) {
                if (_type == PITCH) {
                    y = float(i - pitch_value) * _compression + .5;
                } else { // _type == CLIMB_DIVE
                    y = float(i - actslope) * _compression + .5;
                }

                if (!(i % _div_units)) {  //  At integral multiple of div
                    snprintf(buf, BUFSIZE, "%d", i);

                    // Start by calculating the points and drawing the
                    // left side lines.
                    x_ini = -half_span;
                    x_end2 = half_span;
                    y_end = y;

                    if (i == 0) {
                        // Make zero point wider on left
                        x_ini -= zero_offset;
                        x_end2 += zero_offset;

                        draw_line(x_ini, y, x_end, y);
                        draw_line(x_ini2, y, x_end2, y);

                        draw_text(x_ini - 2.0, y, buf, HUDText::VCENTER|HUDText::RIGHT);
                        draw_text(x_end2 + 2.0, y, buf, HUDText::VCENTER|HUDText::LEFT);

                    } else if (i > 0) {
                        //draw climb bar vertical lines
                        draw_line(x_ini, y - 5.0, x_ini, y);
                        draw_line(x_end2, y - 5.0, x_end2, y);

                        // draw pitch / climb bar
                        draw_line(x_ini, y, x_end, y);
                        draw_line(x_ini2, y, x_end2, y);

                        draw_text(x_ini + 0.5, y - 0.5, buf, HUDText::TOP|HUDText::LEFT);
                        draw_text(x_end2 - 0.5, y - 0.5, buf, HUDText::TOP|HUDText::RIGHT);

                        if (i == 90 && _zenith)
                            draw_zenith(0.0, y);

                    } else { // i < 0
                        float alpha = i * SG_DEGREES_TO_RADIANS / 2.0;
                        y_end = y + (x_end - x_ini) * sin(alpha);

                        float w = (x_end - x_ini) * cos(alpha);
                        x_ini = x_end - w;
                        x_end2 = x_ini2 + w;

                        // draw dive bar vertical lines
                        draw_line(x_end, y + 5.0, x_end, y);
                        draw_line(x_ini2, y + 5.0, x_ini2, y);

                        // draw pitch / dive bars
                        draw_stipple_line(x_ini, y_end, x_end, y);
                        draw_stipple_line(x_ini2, y, x_end2, y_end);

                        float yoffs = 1.0 + (y - y_end) / 4.0;  // too hackish?
                        draw_text(x_ini + 2.0, y_end + yoffs, buf, HUDText::BOTTOM|HUDText::HCENTER);
                        draw_text(x_end2 - 2.0, y_end + yoffs, buf, HUDText::BOTTOM|HUDText::HCENTER);

                        if (i == -90 && _nadir)
                            draw_nadir(0.0, y);
                    }
                }
            }

            // OBJECT LADDER MARK
            // TYPE LINE
            // ATTRIB - ON CONDITION
            // draw appraoch glide slope marker
#ifdef ENABLE_SP_FDM
            if (_glide_slope_marker && ihook) {
                draw_line(-half_span + 15, (_glide_slope - actslope) * _compression,
                        -half_span + hole, (_glide_slope - actslope) * _compression);
                draw_line(half_span - 15, (_glide_slope - actslope) * _compression,
                        half_span - hole, (_glide_slope - actslope) * _compression);
            }
#endif
        }
        _locTextList.draw();

        glLineWidth(0.2);

        _locLineList.draw();

        glEnable(GL_LINE_STIPPLE);
        glLineStipple(1, 0x00FF);
        _locStippleLineList.draw();
        glDisable(GL_LINE_STIPPLE);
    }
    glDisable(GL_CLIP_PLANE0);
    glDisable(GL_CLIP_PLANE1);
    glDisable(GL_CLIP_PLANE2);
    glPopMatrix();
    //*************************************************************

    //*************************************************************
#ifdef ENABLE_SP_FDM
    if (_waypoint_marker) {
        //waypoint marker computation
        float fromwp_lat, towp_lat, fromwp_lon, towp_lon, dist, delx, dely, hyp, theta, brg;

        fromwp_lon = get__longitude() * SGD_DEGREES_TO_RADIANS;
        fromwp_lat = get__latitude() * SGD_DEGREES_TO_RADIANS;
        towp_lon = get__aux2() * SGD_DEGREES_TO_RADIANS;
        towp_lat = get__aux1() * SGD_DEGREES_TO_RADIANS;

        dist = acos(sin(fromwp_lat) * sin(towp_lat) + cos(fromwp_lat)
                * cos(towp_lat) * cos(fabs(fromwp_lon - towp_lon)));
        delx= towp_lat - fromwp_lat;
        dely = towp_lon - fromwp_lon;
        hyp = sqrt(pow(delx, 2) + pow(dely, 2));

        if (hyp != 0)
            theta = asin(dely / hyp);
        else
            theta = 0.0;

        brg = theta * SGD_RADIANS_TO_DEGREES;
        if (brg > 360.0)
            brg = 0.0;
        if (delx < 0)
            brg = 180 - brg;

        // {Brg  = asin(cos(towp_lat)*sin(fabs(fromwp_lon-towp_lon))/ sin(dist));
        // Brg = Brg * SGD_RADIANS_TO_DEGREES; }

        dist *= SGD_RADIANS_TO_DEGREES * 60.0 * 1852.0; //rad->deg->nm->m
        // end waypoint marker computation

        //*********************************************************
        // OBJECT MOVING RETICLE
        // TYPE ARROW
        // waypoint marker
        if (fabs(brg - psi) > 10.0) {
            glPushMatrix();
            glTranslatef(_center_x, _center_y, 0);
            glTranslatef(vel_x, vel_y, 0);
            glRotatef(brg - psi, 0.0, 0.0, -1.0);
            glBegin(GL_LINE_LOOP);
            glVertex2f(-2.5, 20.0);
            glVertex2f(-2.5, 30.0);
            glVertex2f(-5.0, 30.0);
            glVertex2f(0.0, 35.0);
            glVertex2f(5.0, 30.0);
            glVertex2f(2.5, 30.0);
            glVertex2f(2.5, 20.0);
            glEnd();
            glPopMatrix();
        }

        // waypoint marker on heading scale
        if (fabs(brg - psi) < 12.0) {
            if (!_hat) {
                glBegin(GL_LINE_LOOP);
                GLfloat x = (brg - psi) * 60 / 25;
                glVertex2f(x + 320, 240.0);
                glVertex2f(x + 326, 240.0 - 4);
                glVertex2f(x + 323, 240.0 - 4);
                glVertex2f(x + 323, 240.0 - 8);
                glVertex2f(x + 317, 240.0 - 8);
                glVertex2f(x + 317, 240.0 - 4);
                glVertex2f(x + 314, 240.0 - 4);
                glEnd();

            } else { // if (_hat)
                float x = (brg - psi) * 60 / 25 + 320, y = 240.0, r = 5.0;
                float x1, y1;

                glEnable(GL_POINT_SMOOTH);
                glBegin(GL_POINTS);

                for (int count = 0; count <= 200; count++) {
                    float temp = count * SG_PI * 3 / (200.0 * 2.0);
                    float temp1 = temp - (45.0 * SGD_DEGREES_TO_RADIANS);
                    x1 = x + r * cos(temp1);
                    y1 = y + r * sin(temp1);
                    glVertex2f(x1, y1);
                }

                glEnd();
                glDisable(GL_POINT_SMOOTH);
            }

         } //brg<12
     } // if _waypoint_marker
#endif
}//draw


/******************************************************************/
//  draws the zenith symbol (highest possible climb angle i.e. 90 degree climb angle)
//
void HUD::Ladder::draw_zenith(float x, float y)
{
    draw_line(x - 9.0, y, x - 3.0, y + 1.3);
    draw_line(x - 9.0, y, x - 3.0, y - 1.3);

    draw_line(x + 9.0, y, x + 3.0, y + 1.3);
    draw_line(x + 9.0, y, x + 3.0, y - 1.3);

    draw_line(x, y + 9.0, x - 1.3, y + 3.0);
    draw_line(x, y + 9.0, x + 1.3, y + 3.0);

    draw_line(x - 3.9, y + 3.9, x - 3.0, y + 1.3);
    draw_line(x - 3.9, y + 3.9, x - 1.3, y + 3.0);

    draw_line(x + 3.9, y + 3.9, x + 1.3, y + 3.0);
    draw_line(x + 3.9, y + 3.9, x + 3.0, y + 1.3);

    draw_line(x - 3.9, y - 3.9, x - 3.0, y - 1.3);
    draw_line(x - 3.9, y - 3.9, x - 1.3, y - 2.6);

    draw_line(x + 3.9, y - 3.9, x + 3.0, y - 1.3);
    draw_line(x + 3.9, y - 3.9, x + 1.3, y - 2.6);

    draw_line(x - 1.3, y - 2.6, x, y - 27.0);
    draw_line(x + 1.3, y - 2.6, x, y - 27.0);
}


//  draws the nadir symbol (lowest possible dive angle i.e. 90 degree dive angle))
//
void HUD::Ladder::draw_nadir(float x, float y)
{
    const float R = 7.5;

    draw_circle(x, y, R);
    draw_line(x, y + R, x, y + 22.5); // line above the circle
    draw_line(x - R, y, x + R, y);    // line at middle of circle

    float theta = asin(2.5 / R);
    float theta1 = asin(5.0 / R);
    float x1, y1, x2, y2;

    x1 = x + R * cos(theta);
    y1 = y + 2.5;
    x2 = x + R * cos((180.0 * SGD_DEGREES_TO_RADIANS) - theta);
    y2 = y + 2.5;
    draw_line(x1, y1, x2, y2);

    x1 = x + R * cos(theta1);
    y1 = y + 5.0;
    x2 = x + R * cos((180.0 * SGD_DEGREES_TO_RADIANS) - theta1);
    y2 = y + 5.0;
    draw_line(x1, y1, x2, y2);

    x1 = x + R * cos((180.0 * SGD_DEGREES_TO_RADIANS) + theta);
    y1 = y - 2.5;
    x2 = x + R * cos((360.0 * SGD_DEGREES_TO_RADIANS) - theta);
    y2 = y - 2.5;
    draw_line(x1, y1, x2, y2);

    x1 = x + R * cos((180.0 * SGD_DEGREES_TO_RADIANS) + theta1);
    y1 = y - 5.0;
    x2 = x + R * cos((360.0 * SGD_DEGREES_TO_RADIANS) - theta1);
    y2 = y - 5.0;
    draw_line(x1, y1, x2, y2);
}