citylimits/core/sprite.cpp

/* sprite.cpp
 *
 * Micropolis, Unix Version.  This game was released for the Unix platform
 * in or about 1990 and has been modified for inclusion in the One Laptop
 * Per Child program.  Copyright (C) 1989 - 2007 Electronic Arts Inc.  If
 * you need assistance with this program, you may contact:
 *   http://wiki.laptop.org/go/Micropolis  or email  micropolis@laptop.org.
 *
 * 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 3 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, see <http://www.gnu.org/licenses/>.
 *
 *             ADDITIONAL TERMS per GNU GPL Section 7
 *
 * No trademark or publicity rights are granted.  This license does NOT
 * give you any right, title or interest in the trademark SimCity or any
 * other Electronic Arts trademark.  You may not distribute any
 * modification of this program using the trademark SimCity or claim any
 * affliation or association with Electronic Arts Inc. or its employees.
 *
 * Any propagation or conveyance of this program must include this
 * copyright notice and these terms.
 *
 * If you convey this program (or any modifications of it) and assume
 * contractual liability for the program to recipients of it, you agree
 * to indemnify Electronic Arts for any liability that those contractual
 * assumptions impose on Electronic Arts.
 *
 * You may not misrepresent the origins of this program; modified
 * versions of the program must be marked as such and not identified as
 * the original program.
 *
 * This disclaimer supplements the one included in the General Public
 * License.  TO THE FULLEST EXTENT PERMISSIBLE UNDER APPLICABLE LAW, THIS
 * PROGRAM IS PROVIDED TO YOU "AS IS," WITH ALL FAULTS, WITHOUT WARRANTY
 * OF ANY KIND, AND YOUR USE IS AT YOUR SOLE RISK.  THE ENTIRE RISK OF
 * SATISFACTORY QUALITY AND PERFORMANCE RESIDES WITH YOU.  ELECTRONIC ARTS
 * DISCLAIMS ANY AND ALL EXPRESS, IMPLIED OR STATUTORY WARRANTIES,
 * INCLUDING IMPLIED WARRANTIES OF MERCHANTABILITY, SATISFACTORY QUALITY,
 * FITNESS FOR A PARTICULAR PURPOSE, NONINFRINGEMENT OF THIRD PARTY
 * RIGHTS, AND WARRANTIES (IF ANY) ARISING FROM A COURSE OF DEALING,
 * USAGE, OR TRADE PRACTICE.  ELECTRONIC ARTS DOES NOT WARRANT AGAINST
 * INTERFERENCE WITH YOUR ENJOYMENT OF THE PROGRAM; THAT THE PROGRAM WILL
 * MEET YOUR REQUIREMENTS; THAT OPERATION OF THE PROGRAM WILL BE
 * UNINTERRUPTED OR ERROR-FREE, OR THAT THE PROGRAM WILL BE COMPATIBLE
 * WITH THIRD PARTY SOFTWARE OR THAT ANY ERRORS IN THE PROGRAM WILL BE
 * CORRECTED.  NO ORAL OR WRITTEN ADVICE PROVIDED BY ELECTRONIC ARTS OR
 * ANY AUTHORIZED REPRESENTATIVE SHALL CREATE A WARRANTY.  SOME
 * JURISDICTIONS DO NOT ALLOW THE EXCLUSION OF OR LIMITATIONS ON IMPLIED
 * WARRANTIES OR THE LIMITATIONS ON THE APPLICABLE STATUTORY RIGHTS OF A
 * CONSUMER, SO SOME OR ALL OF THE ABOVE EXCLUSIONS AND LIMITATIONS MAY
 * NOT APPLY TO YOU.
 */

/**
 * @file sprite.cpp
 * @brief Manages sprite objects and their behavior in Micropolis.
 *
 * This file defines functions related to the creation, movement,
 * interaction, and destruction of various sprites such as trains,
 * helicopters, airplanes, ships, monsters, tornadoes, and explosions
 * within the Micropolis game. It handles the logic for sprite
 * behavior, including movement patterns, interactions with other
 * sprites and the game map, and event-triggered actions like
 * explosions and sound effects.
 */


////////////////////////////////////////////////////////////////////////


#include "micropolis.h"
#include "text.h"


////////////////////////////////////////////////////////////////////////


#define TRA_GROOVE_X -39
#define TRA_GROOVE_Y 6
#define BUS_GROOVE_X -39
#define BUS_GROOVE_Y 6


////////////////////////////////////////////////////////////////////////


/**
 * Create and initialize a sprite.
 * @param name Name of the sprite (always \c "").
 * @param type Type pf the sprite. @see SpriteType.
 * @param x X coordinate of the sprite (in pixels).
 * @param y Y coordinate of the sprite (in pixels).
 * @return New sprite object.
 */
SimSprite *Micropolis::newSprite(const std::string &name, int type, int x, int y)
{
    SimSprite *sprite;

    // If a sprite is available at the pool, use one.
    // else, allocate a new one.
    if (freeSprites) {
        sprite = freeSprites;
        freeSprites = sprite->next;
    } else {
        sprite = (SimSprite *)newPtr(sizeof (SimSprite));
    }

    sprite->name = name;
    sprite->type = type;

    initSprite(sprite, x, y);

    sprite->next = spriteList;
    spriteList = sprite;

    return sprite;
}


/** Re-initialize an existing sprite.
 * @param sprite Sprite to re-use.
 * @param x      New x coordinate of the sprite (in pixels?).
 * @param y      New y coordinate of the sprite (in pixels?).
 * @todo Make derived classes for each type.
 * @todo Move code to (derived) #SimSprite methods.
 */
void Micropolis::initSprite(SimSprite *sprite, int x, int y)
{
    sprite->x = x;
    sprite->y = y;
    sprite->frame = 0;
    sprite->origX = 0;
    sprite->origY = 0;
    sprite->destX = 0;
    sprite->destY = 0;
    sprite->count = 0;
    sprite->soundCount = 0;
    sprite->dir = 0;
    sprite->newDir = 0;
    sprite->step = 0;
    sprite->flag = 0;
    sprite->control = -1;
    sprite->turn = 0;
    sprite->accel = 0;
    sprite->speed = 100;

    if (globalSprites[sprite->type] == NULL) {
        globalSprites[sprite->type] = sprite;
    }

    switch (sprite->type) {

        case SPRITE_TRAIN:
            sprite->width = 32;
            sprite->height = 32;
            sprite->xOffset = 32;
            sprite->yOffset = -16;
            sprite->xHot = 40;
            sprite->yHot = -8;
            sprite->frame = 1;
            sprite->dir = 4;
            break;

        case SPRITE_SHIP:
            sprite->width = 48;
            sprite->height = 48;
            sprite->xOffset = 32;
            sprite->yOffset = -16;
            sprite->xHot = 48;
            sprite->yHot = 0;

            if (x < (4 <<4)) {
                sprite->frame = 3;
            } else if (x >= ((WORLD_W - 4) <<4)) {
                sprite->frame = 7;
            } else if (y < (4 <<4)) {
                sprite->frame = 5;
            } else if (y >= ((WORLD_H - 4) <<4)) {
                sprite->frame = 1;
            } else {
                sprite->frame = 3;
            }

            sprite->newDir = sprite->frame;
            sprite->dir = 10;
            sprite->count = 1;
            break;

        case SPRITE_MONSTER:
            sprite->width = 48;
            sprite->height = 48;
            sprite->xOffset = 24;
            sprite->yOffset = 0;
            sprite->xHot = 40;
            sprite->yHot = 16;

            if (x > ((WORLD_W <<4) / 2)) {
                if (y > ((WORLD_H <<4) / 2)) {
                    sprite->frame = 10;
                } else {
                    sprite->frame = 7;
                }
            } else if (y > ((WORLD_H <<4) / 2)) {
                sprite->frame = 1;
            } else {
                sprite->frame = 4;
            }

            sprite->count = 1000;
            sprite->destX = pollutionMaxX <<4;
            sprite->destY = pollutionMaxY <<4;
            sprite->origX = sprite->x;
            sprite->origY = sprite->y;
            break;

        case SPRITE_HELICOPTER:
            sprite->width = 32;
            sprite->height = 32;
            sprite->xOffset = 32;
            sprite->yOffset = -16;
            sprite->xHot = 40;
            sprite->yHot = -8;
            sprite->frame = 5;
            sprite->count = 1500;
            sprite->destX = getRandom((WORLD_W <<4) - 1);
            sprite->destY = getRandom((WORLD_H <<4) - 1);
            sprite->origX = x - 30;
            sprite->origY = y;
            break;

        case SPRITE_AIRPLANE:
            sprite->width = 48;
            sprite->height = 48;
            sprite->xOffset = 24;
            sprite->yOffset = 0;
            sprite->xHot = 48;
            sprite->yHot = 16;
            if (x > ((WORLD_W - 20) <<4)) {
                sprite->x -= 100 + 48;
                sprite->destX = sprite->x - 200;
                sprite->frame = 7;
            } else {
                sprite->destX = sprite->x + 200;
                sprite->frame = 11;
            }
            sprite->destY = sprite->y;
            break;

        case SPRITE_TORNADO:
            sprite->width = 48;
            sprite->height = 48;
            sprite->xOffset = 24;
            sprite->yOffset = 0;
            sprite->xHot = 40;
            sprite->yHot = 36;
            sprite->frame = 1;
            sprite->count = 200;
            break;

        case SPRITE_EXPLOSION:
            sprite->width = 48;
            sprite->height = 48;
            sprite->xOffset = 24;
            sprite->yOffset = 0;
            sprite->xHot = 40;
            sprite->yHot = 16;
            sprite->frame = 1;
            break;

        case SPRITE_BUS:
            sprite->width = 32;
            sprite->height = 32;
            sprite->xOffset = 30;
            sprite->yOffset = -18;
            sprite->xHot = 40;
            sprite->yHot = -8;
            sprite->frame = 1;
            sprite->dir = 1;
            break;

    }
}


/**
 * Destroy all sprites by de-activating them all (setting their
 * SimSprite::frame to 0).
 */
void Micropolis::destroyAllSprites()
{
    SimSprite *sprite;

    for (sprite = spriteList; sprite != NULL; sprite = sprite->next) {
        sprite->frame = 0;
    }
}


/**
 * Destroy the sprite by taking it out of the active list.
 * @param sprite Sprite to destroy.
 * @todo Break the connection between any views that are following this sprite.
 */
void Micropolis::destroySprite(SimSprite *sprite)
{
    SimSprite **sp;

    if (globalSprites[sprite->type] == sprite) {
        globalSprites[sprite->type] = (SimSprite *)NULL;
    }

    for (sp = &spriteList; *sp != NULL; sp = &((*sp)->next)) {
        if (sprite == (*sp)) {
            *sp = sprite->next;
            break;
        }
    }

    sprite->next = freeSprites;
    freeSprites = sprite;
}


/**
 * Return the sprite of the give type, if available.
 * @param type Type of the sprite.
 * @return Pointer to the active sprite if avaiable, else \c NULL.
 */
SimSprite *Micropolis::getSprite(int type)
{
    SimSprite *sprite = globalSprites[type];
    if (sprite == NULL || sprite->frame == 0) {
        return (SimSprite *)NULL;
    } else {
        return sprite;
    }
}


/**
 * Make a sprite either by re-using the old one, or by making a new one.
 * @param type Sprite type of the new sprite.
 * @param x    X coordinate of the new sprite.
 * @param y    Y coordinate of the new sprite.
 */
SimSprite *Micropolis::makeSprite(int type, int x, int y)
{
    SimSprite *sprite;

    sprite = globalSprites[type];
    if (sprite == NULL) {
        sprite = newSprite("", type, x, y);
    } else {
        initSprite(sprite, x, y);
    }
    return sprite;
}


/**
 * Get character from the map.
 * @param x X coordinate in pixels.
 * @param y Y coordinate in pixels.
 * @return Map character if on-map, or \c -1 if off-map.
 */
short Micropolis::getChar(int x, int y)
{
    // Convert sprite coordinates to tile coordinates.
    x >>= 4;
    y >>= 4;

    if (!testBounds(x, y)) {
        return -1;
    } else {
        return map[x][y] & LOMASK;
    }
}


/**
 * Turn.
 * @param p Present direction (1..8).
 * @param d Destination direction (1..8).
 * @return New direction.
 * @todo Remove local magic constants and document the code.
 */
short Micropolis::turnTo(int p, int d)
{
    if (p == d) {
        return p;
    }

    if (p < d) {
        if (d - p < 4) {
            p++;
        } else {
            p--;
        }
    } else {
        if (p - d < 4) {
            p--;
        } else {
            p++;
        }
    }

    if (p > 8) {
        p = 1;
    }

    if (p < 1) {
        p = 8;
    }

    return p;
}

/** ???
 * @todo Figure out what this function is doing.
 * @todo Remove local magic constants and document the code.
 */
bool Micropolis::tryOther(int Tpoo, int Told, int Tnew)
{
    short z;

    z = Told + 4;

    if (z > 8) {
        z -= 8;
    }

    if (Tnew != z) {
        return false;
    }

    if (Tpoo == POWERBASE || Tpoo == POWERBASE + 1
          || Tpoo == RAILBASE || Tpoo == RAILBASE + 1) {
        return true;
    }

    return false;
}


/**
 * Check whether a sprite is still entirely on-map.
 * @param sprite Sprite to check.
 * @return Sprite is at least partly off-map.
 */
bool Micropolis::spriteNotInBounds(SimSprite *sprite)
{
    int x = sprite->x + sprite->xHot;
    int y = sprite->y + sprite->yHot;

    return x < 0 || y < 0 || x >= (WORLD_W <<4) || y >= (WORLD_H <<4);
}

/**
 * Get direction (0..8?) to get from starting point to destination point.
 * @param orgX X coordinate starting point.
 * @param orgY Y coordinate starting point.
 * @param desX X coordinate destination point.
 * @param desY Y coordinate destination point.
 * @return Direction to go in.
 * @todo Remove local magic constants and document the code.
 * @bug Has a condition that never holds.
 */
short Micropolis::getDir(int orgX, int orgY, int desX, int desY)
{
    static const short Gdtab[13] = { 0, 3, 2, 1, 3, 4, 5, 7, 6, 5, 7, 8, 1 };
    int dispX, dispY, z;

    dispX = desX - orgX;
    dispY = desY - orgY;

    if (dispX < 0) {
        if (dispY < 0) {
            z = 11;
        } else {
            z = 8;
        }
    } else {
        if (dispY < 0) {
            z = 2;
        } else {
            z = 5;
        }
    }

    dispX = absoluteValue(dispX);
    dispY = absoluteValue(dispY);
    absDist = dispX + dispY;

    if (dispX * 2 < dispY) {
        z++;
    } else if (dispY * 2 < dispY) {  // XXX This never holds!!
        z--;
    }

    if (z < 0 || z > 12) {
        z = 0;
    }

    return Gdtab[z];
}


/**
 * Compute Manhattan distance between two points.
 * @param x1 X coordinate first point.
 * @param y1 Y coordinate first point.
 * @param x2 X coordinate second point.
 * @param y2 Y coordinate second point.
 * @return Manhattan distance between both points.
 */
int Micropolis::getDistance(int x1, int y1, int x2, int y2)
{
    return absoluteValue(x1 - x2) + absoluteValue(y1 - y2);
}


/**
 * Check whether two sprites collide with each other.
 * @param s1 First sprite.
 * @param s2 Second sprite.
 * @return Sprites are colliding.
 */
bool Micropolis::checkSpriteCollision(SimSprite *s1, SimSprite *s2)
{
    return s1->frame != 0 && s2->frame != 0 &&
           getDistance(s1->x + s1->xHot, s1->y + s1->yHot,
                       s2->x + s2->xHot, s2->y + s2->yHot) < 30;
}


/**
 * Move all sprites.
 *
 * Sprites with SimSprite::frame == 0 are removed.
 * @todo It uses SimSprite::name[0] == '\0' as condition which seems stupid.
 * @todo Micropolis::destroySprite modifies the Micropolis::spriteList
 *       while we loop over it.
 */
void Micropolis::moveObjects()
{
    SimSprite *sprite;

    if (!simSpeed) {
        return;
    }

    spriteCycle++;

    for (sprite = spriteList; sprite != NULL;) {
        if (sprite->frame > 0) {
            switch (sprite->type) {

                case SPRITE_TRAIN:
                    doTrainSprite(sprite);
                    break;

                case SPRITE_HELICOPTER:
                    doCopterSprite(sprite);
                    break;

                case SPRITE_AIRPLANE:
                    doAirplaneSprite(sprite);
                    break;

                case SPRITE_SHIP:
                    doShipSprite(sprite);
                    break;

                case SPRITE_MONSTER:
                    doMonsterSprite(sprite);
                    break;

                case SPRITE_TORNADO:
                    doTornadoSprite(sprite);
                    break;

                case SPRITE_EXPLOSION:
                    doExplosionSprite(sprite);
                    break;

                case SPRITE_BUS:
                    doBusSprite(sprite);
                    break;

            }

            sprite = sprite->next;

        } else {

            if (sprite->name[0] == '\0') {
                SimSprite *s = sprite;
                sprite = sprite->next;
                destroySprite(s);
            } else {
                sprite = sprite->next;
            }

        }
    }
}


/**
 * Move train sprite.
 * @param sprite Train sprite.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doTrainSprite(SimSprite *sprite)
{
    /* Offset in pixels of sprite x and y to map tile */
    static const short Cx[4] = {   0,  16,   0, -16 };
    static const short Cy[4] = { -16,   0,  16,   0 };
    /* X and Y movement of the sprite in pixels */
    static const short Dx[5] = {   0,   4,   0,  -4,   0 };
    static const short Dy[5] = {  -4,   0,   4,   0,   0 };

    static const short TrainPic2[5] = { 1, 2, 1, 2, 5 };
    short z, dir, dir2;
    short c;

    if (sprite->frame == 3 || sprite->frame == 4) {
        sprite->frame = TrainPic2[sprite->dir];
    }

    sprite->x += Dx[sprite->dir];
    sprite->y += Dy[sprite->dir];

    if ((spriteCycle & 3) == 0) {

        dir = getRandom16() & 3;
        for (z = dir; z < dir + 4; z++) {
            dir2 = z & 3;

            if (sprite->dir != 4) {
                if (dir2 == ((sprite->dir + 2) & 3)) {
                    continue;
                }
            }

            c = getChar(sprite->x + Cx[dir2] + 48, sprite->y + Cy[dir2]);

            if ((c >= RAILBASE && c <= LASTRAIL) /* track? */
                      || c == RAILVPOWERH || c == RAILHPOWERV) {

                if (sprite->dir != dir2 && sprite->dir != 4) {

                    if (sprite->dir + dir2 == 3) {
                        sprite->frame = 3;
                    } else {
                        sprite->frame = 4;
                    }

                } else {
                    sprite->frame = TrainPic2[dir2];
                }

                if (c == HRAIL || c == VRAIL) {
                    sprite->frame = 5;
                }

                sprite->dir = dir2;
                return;
            }
        }

        if (sprite->dir == 4) {
            sprite->frame = 0;
            return;
        }

        sprite->dir = 4;
    }
}

/**
 * Move helicopter sprite.
 * @param sprite Helicopter sprite.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doCopterSprite(
  SimSprite *sprite)
{
    static const short CDx[9] = { 0,  0,  3,  5,  3,  0, -3, -5, -3 };
    static const short CDy[9] = { 0, -5, -3,  0,  3,  5,  3,  0, -3 };

    if (sprite->soundCount > 0) {
        sprite->soundCount--;
    }

    if (sprite->control < 0) {

        if (sprite->count > 0) {
            sprite->count--;
        }

        if (sprite->count == 0) {

            /* Attract copter to monster so it blows up more often */
            SimSprite *s = getSprite(SPRITE_MONSTER);

            if (s != NULL) {
                sprite->destX = s->x;
                sprite->destY = s->y;
            } else {

                /* Attract copter to tornado so it blows up more often */
                s = getSprite(SPRITE_TORNADO);

                if (s != NULL) {
                    sprite->destX = s->x;
                    sprite->destY = s->y;
                } else {
                    sprite->destX = sprite->origX;
                    sprite->destY = sprite->origY;
                }

            }
        }

        if (sprite->count == 0) { /* land */
            getDir(sprite->x, sprite->y, sprite->origX, sprite->origY);

            if (absDist < 30) {
                sprite->frame = 0;
                return;
            }

        }

    } else {

        getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);

        if (absDist < 16) {
            sprite->destX = sprite->origX;
            sprite->destY = sprite->origY;
            sprite->control = -1;
        }

    }

    if (sprite->soundCount == 0) { /* send report  */

        // Convert sprite coordinates to world coordinates.
        short x = (sprite->x + 48) / 16;
        short y = sprite->y / 16;

        if (x >= 0 && x < WORLD_W && y >= 0 && y < WORLD_H) {

            /* Don changed from 160 to 170 to shut the #$%#$% thing up! */

            int chopperX = x + 1;
            int chopperY = y + 1;
            if (trafficDensityMap.worldGet(x, y) > 170 && (getRandom16() & 7) == 0) {
                sendMessage(MESSAGE_HEAVY_TRAFFIC, chopperX, chopperY, true);
                makeSound("city", "HeavyTraffic", chopperX, chopperY); /* chopper */
                sprite->soundCount = 200;
            }

        }

    }

    short z = sprite->frame;

    if ((spriteCycle & 3) == 0) {
        short d = getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);
        z = turnTo(z, d);
        sprite->frame = z;
    }

    sprite->x += CDx[z];
    sprite->y += CDy[z];
}


/**
 * Move airplane sprite.
 * @param sprite Airplane sprite.
 * @todo Remove local magic constants and document the code.
 * @todo absDist gets updated by Micropolis::getDir(), which is not always
 *       called before reading it (or worse, we just turned towards the old
 *       destination).
 */
void Micropolis::doAirplaneSprite(
  SimSprite *sprite)
{
    static const short CDx[12] = { 0,  0,  6, 8, 6, 0, -6, -8, -6, 8, 8, 8 };
    static const short CDy[12] = { 0, -8, -6, 0, 6, 8,  6,  0, -6, 0, 0, 0 };

    short z = sprite->frame;

    if ((spriteCycle % 5) == 0) {

        if (z > 8) { /* TakeOff  */
            z--;
            if (z < 9) {
                z = 3;
            }
            sprite->frame = z;
        } else { /* goto destination */
            short d = getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);
            z = turnTo(z, d);
            sprite->frame = z;
        }

    }

    if (absDist < 50) { /* at destination  */
        sprite->destX = getRandom((WORLD_W * 16) + 100) - 50;
        sprite->destY = getRandom((WORLD_H * 16) + 100) - 50;
    }

    /* deh added test for enableDisasters */
    if (enableDisasters) {
        SimSprite *s;
        bool explode = false;

        /* Check whether another sprite is near enough to collide with */
        for (s = spriteList; s != NULL; s = s->next) {
            if (s->frame == 0 || s == sprite) {
                /* Non-active sprite, or self: skip */
                continue;
            }

            if ((s->type == SPRITE_HELICOPTER || s->type == SPRITE_AIRPLANE)
                                          && checkSpriteCollision(sprite, s)) {
                explodeSprite(s);
                explode = true;
            }
        }

        if (explode) {
            explodeSprite(sprite);
        }
    }

    sprite->x += CDx[z];
    sprite->y += CDy[z];

    if (spriteNotInBounds(sprite)) {
        sprite->frame = 0;
    }
}


/**
 * Move ship sprite.
 * @param sprite Ship sprite.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doShipSprite(SimSprite *sprite)
{
    static const short BDx[9] = { 0,  0,  1,  1,  1,  0, -1, -1, -1 };
    static const short BDy[9] = { 0, -1, -1,  0,  1,  1,  1,  0, -1 };
    static const short BPx[9] = { 0,  0,  2,  2,  2,  0, -2, -2, -2 };
    static const short BPy[9] = { 0, -2, -2,  0,  2,  2,  2,  0, -2 };
    static const short BtClrTab[8] = { RIVER, CHANNEL, POWERBASE, POWERBASE + 1,
                                       RAILBASE, RAILBASE + 1, BRWH, BRWV };
    short x, y, z, t = RIVER;
    short tem, pem;

    if (sprite->soundCount > 0) {
        sprite->soundCount--;
    }

    if (!sprite->soundCount) {

        if ((getRandom16() & 3) == 1) {

            // Convert sprite coordinates to tile coordinates.
            int shipX = sprite->x >>4;
            int shipY = sprite->y >>4;

            if (scenario == SC_SAN_FRANCISCO && getRandom(10) < 5) {
                makeSound("city", "FogHornLow", shipX, shipY);
            } else {
                makeSound("city", "HonkHonkLow", shipX, shipY);
            }

        }

        sprite->soundCount = 200;
    }

    if (sprite->count > 0) {
        sprite->count--;
    }

    if (sprite->count == 0) {

        sprite->count = 9;

        if (sprite->frame != sprite->newDir) {
            sprite->frame = turnTo(sprite->frame, sprite->newDir);
            return;
        }

        tem = getRandom16() & 7;

        for (pem = tem; pem < (tem + 8); pem++) {

            z = (pem & 7) + 1;

            if (z == sprite->dir) {
                continue;
            }

            x = ((sprite->x + (48 - 1)) >>4) + BDx[z];
            y = (sprite->y >>4) + BDy[z];

            if (testBounds(x, y)) {

                t = map[x][y] & LOMASK;

                if (t == CHANNEL || t == BRWH || t == BRWV
                                                    || tryOther(t, sprite->dir, z)) {

                    sprite->newDir = z;
                    sprite->frame = turnTo(sprite->frame, sprite->newDir);
                    sprite->dir = z + 4;

                    if (sprite->dir > 8) {
                        sprite->dir -= 8;
                    }

                    break;
                }
            }
        }

        if (pem == (tem + 8)) {
            sprite->dir = 10;
            sprite->newDir = (getRandom16() & 7) + 1;
        }

    } else {

        z = sprite->frame;

        if (z == sprite->newDir)  {
            sprite->x += BPx[z];
            sprite->y += BPy[z];
        }
    }

    if (spriteNotInBounds(sprite)) {
        sprite->frame = 0;
        return;
    }

    for (z = 0; z < 8; z++) {

        if (t == BtClrTab[z]) {
            break;
        }

        if (z == 7) {
            explodeSprite(sprite);
            destroyMapTile(sprite->x + 48, sprite->y);
        }

    }
}


/**
 * Move monster sprite.
 *
 * There are 16 monster sprite frames:
 *
 * Frame 0: NorthEast Left Foot
 * Frame 1: NorthEast Both Feet
 * Frame 2: NorthEast Right Foot
 * Frame 3: SouthEast Right Foot
 * Frame 4: SouthEast Both Feet
 * Frame 5: SouthEast Left Foot
 * Frame 6: SouthWest Right Foot
 * Frame 7: SouthWest Both Feet
 * Frame 8: SouthWest Left Foot
 * Frame 9: NorthWest Left Foot
 * Frame 10: NorthWest Both Feet
 * Frame 11: NorthWest Right Foot
 * Frame 12: North Left Foot
 * Frame 13: East Left Foot
 * Frame 14: South Right Foot
 * Frame 15: West Right Foot
 *
 * @param sprite Monster sprite.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doMonsterSprite(SimSprite *sprite)
{
    static const short Gx[5] = {  2,  2, -2, -2,  0 };
    static const short Gy[5] = { -2,  2,  2, -2,  0 };
    static const short ND1[4] = {  0,  1,  2,  3 };
    static const short ND2[4] = {  1,  2,  3,  0 };
    static const short nn1[4] = {  2,  5,  8, 11 };
    static const short nn2[4] = { 11,  2,  5,  8 };
    short d, z, c;

    if (sprite->soundCount > 0) {
        sprite->soundCount--;
    }

    if (sprite->control < 0) {
        /* business as usual */

        if (sprite->control == -2) {

            d = (sprite->frame - 1) / 3;
            z = (sprite->frame - 1) % 3;

            if (z == 2) {
                sprite->step = 0;
            }

            if (z == 0) {
                sprite->step = 1;
            }

            if (sprite->step) {
                z++;
            } else {
                z--;
            }

            c = getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);

            if (absDist < 18) {

                sprite->control = -1;
                sprite->count = 1000;
                sprite->flag = 1;
                sprite->destX = sprite->origX;
                sprite->destY = sprite->origY;

            } else {

                c = (c - 1) / 2;

                if ((c != d && getRandom(5) == 0) || getRandom(20) == 0) {

                    int diff = (c - d) & 3;

                    if (diff == 1 || diff == 3) {
                        d = c;
                    } else {

                        if (getRandom16() & 1) {
                            d++;
                        } else {
                            d--;
                        }

                        d &= 3;
                    }
                } else {

                    if (getRandom(20) == 0) {

                        if (getRandom16() & 1) {
                            d++;
                        } else {
                            d--;
                        }

                        d &= 3;
                    }
                }
            }
        } else {

            d = (sprite->frame - 1) / 3;

            if (d < 4) { /* turn n s e w */

                z = (sprite->frame - 1) % 3;

                if (z == 2) {
                    sprite->step = 0;
                }

                if (z == 0) {
                    sprite->step = 1;
                }

                if (sprite->step) {
                    z++;
                } else {
                    z--;
                }

                getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);

                if (absDist < 60) {

                    if (sprite->flag == 0) {

                        sprite->flag = 1;
                        sprite->destX = sprite->origX;
                        sprite->destY = sprite->origY;

                    } else {

                        sprite->frame = 0;
                        return;

                    }

                }

                c = getDir(sprite->x, sprite->y, sprite->destX, sprite->destY);
                c = (c - 1) / 2;

                if ((c != d) && (!getRandom(10))) {

                    if (getRandom16() & 1) {
                        z = ND1[d];
                    } else {
                        z = ND2[d];
                    }

                    d = 4;

                    if (!sprite->soundCount) {
                        // Convert sprite coordinates to tile coordinates.
                        int monsterX = sprite->x >>4;
                        int monsterY = sprite->y >>4;
                        makeSound("city", "Monster", monsterX, monsterY); /* monster */
                        sprite->soundCount = 50 + getRandom(100);
                    }

                }

            } else {

                d = 4;
                c = sprite->frame;
                z = (c - 13) & 3;

                if (!(getRandom16() & 3)) {

                    if (getRandom16() & 1) {
                        z = nn1[z];
                    } else {
                        z = nn2[z];
                    }

                    d = (z - 1) / 3;
                    z = (z - 1) % 3;

                }

            }

        }

    } else {

          /* somebody's taken control of the monster */

          d = sprite->control;
          z = (sprite->frame - 1) % 3;

          if (z == 2) {
              sprite->step = 0;
          }

          if (z == 0) {
              sprite->step = 1;
          }

          if (sprite->step) {
              z++;
          } else {
              z--;
          }

    }

    z = d * 3 + z + 1;

    if (z > 16) {
        z = 16;
    }

    sprite->frame = z;

    sprite->x += Gx[d];
    sprite->y += Gy[d];

    if (sprite->count > 0) {
        sprite->count--;
    }

    c = getChar(sprite->x + sprite->xHot, sprite->y + sprite->yHot);

    if (c == -1
          || (c == RIVER && sprite->count != 0 && sprite->control == -1)) {
        sprite->frame = 0; /* kill scary monster */
    }

    {
        SimSprite *s;
        for (s = spriteList; s != NULL; s = s->next) {
            if (s->frame != 0 &&
                (s->type == SPRITE_AIRPLANE || s->type == SPRITE_HELICOPTER
                 || s->type == SPRITE_SHIP || s->type == SPRITE_TRAIN) &&
                checkSpriteCollision(sprite, s)) {
                explodeSprite(s);
            }
        }
    }

    destroyMapTile(sprite->x + 48, sprite->y + 16);
}

/**
 * Move tornado.
 * @param sprite Tornado sprite to move.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doTornadoSprite(SimSprite *sprite)
{
    static const short CDx[9] = {  2,  3,  2,  0, -2, -3 };
    static const short CDy[9] = { -2,  0,  2,  3,  2,  0 };
    short z;

    z = sprite->frame;

    if (z == 2) {

        /* cycle animation... post Rel */

        if (sprite->flag) {
            z = 3;
        } else {
            z = 1;
        }

    } else {

        if (z == 1) {
            sprite->flag = 1;
        } else {
            sprite->flag = 0;
        }

        z = 2;
    }

    if (sprite->count > 0) {
        sprite->count--;
    }

    sprite->frame = z;

    {
        SimSprite *s;
        for (s = spriteList; s != NULL; s = s->next) {
            if (s->frame != 0 &&
                (s->type == SPRITE_AIRPLANE || s->type == SPRITE_HELICOPTER
                 || s->type == SPRITE_SHIP || s->type == SPRITE_TRAIN) &&
                checkSpriteCollision(sprite, s)) {
                explodeSprite(s);
            }
        }
    }

    z = getRandom(5);
    sprite->x += CDx[z];
    sprite->y += CDy[z];

    if (spriteNotInBounds(sprite)) {
        sprite->frame = 0;
    }

    if (sprite->count != 0 && getRandom(500) == 0) {
        sprite->frame = 0;
    }

    destroyMapTile(sprite->x + 48, sprite->y + 40);
}


/**
 * 'Move' fire sprite.
 * @param sprite Fire sprite.
 */
void Micropolis::doExplosionSprite(SimSprite *sprite)
{
    short x, y;

    if ((spriteCycle & 1) == 0) {

        if (sprite->frame == 1) {
            // Convert sprite coordinates to tile coordinates.
            int explosionX = sprite->x >>4;
            int explosionY = sprite->y >>4;
            makeSound("city", "ExplosionHigh", explosionX, explosionY); /* explosion */
            x = (sprite->x >>4) + 3;
            y = (sprite->y >>4);
            sendMessage(MESSAGE_EXPLOSION_REPORTED, x, y);
        }

        sprite->frame++;
    }

    if (sprite->frame > 6) {
        sprite->frame = 0;

        startFire(sprite->x + 48 - 8, sprite->y + 16);
        startFire(sprite->x + 48 - 24, sprite->y);
        startFire(sprite->x + 48 + 8, sprite->y);
        startFire(sprite->x + 48 - 24, sprite->y + 32);
        startFire(sprite->x + 48 + 8, sprite->y + 32);
    }
}


/**
 * Move bus sprite.
 * @param sprite Bus sprite.
 * @todo Remove local magic constants and document the code.
 */
void Micropolis::doBusSprite(SimSprite *sprite)
{
    static const short Dx[5] = {   0,   1,   0,  -1,   0 };
    static const short Dy[5] = {  -1,   0,   1,   0,   0 };
    static const short Dir2Frame[4] = { 1, 2, 1, 2 };
    int dx, dy, tx, ty, otx, oty;
    int turned = 0;
    int speed = 0;
    int z;

#ifdef DEBUGBUS
    printf("Bus dir %d turn %d frame %d\n",
           sprite->dir, sprite->turn, sprite->frame);
#endif

    if (sprite->turn) {

        if (sprite->turn < 0) { /* ccw */

            if (sprite->dir & 1) { /* up or down */
                sprite->frame = 4;
            } else { /* left or right */
                sprite->frame = 3;
            }

            sprite->turn++;
            sprite->dir = (sprite->dir - 1) & 3;

        } else { /* cw */

            if (sprite->dir & 1) { /* up or down */
                sprite->frame = 3;
            } else { /* left or right */
                sprite->frame = 4;
            }

            sprite->turn--;
            sprite->dir = (sprite->dir + 1) & 3;

        }

        turned = 1;

    } else {

        /* finish turn */
        if ((sprite->frame == 3) ||
            (sprite->frame == 4)) {
            turned = 1;
            sprite->frame = Dir2Frame[sprite->dir];
        }
    }

    if (sprite->speed == 0) {

        /* brake */
        dx = 0; dy = 0;

    } else { /* cruise at traffic speed */

        tx = (sprite->x + sprite->xHot) >>5;
        ty = (sprite->y + sprite->yHot) >>5;

        if (tx >= 0 && tx < WORLD_W_2 && ty >= 0 && ty < WORLD_H_2) {

            z = trafficDensityMap.worldGet(tx << 1, ty << 1) >>6;

            if (z > 1) {
                z--;
            }

        } else {

            z = 0;

        }

        switch (z) {

            case 0:
                speed = 8;
                break;

            case 1:
                speed = 4;
                break;

            case 2:
                speed = 1;
                break;

        }

        /* govern speed */
        if (speed > sprite->speed) {
            speed = sprite->speed;
        }

        if (turned) {

#ifdef DEBUGBUS
          printf("turned\n");
#endif

            if (speed > 1) {
                speed = 1;
            }

            dx = Dx[sprite->dir] * speed;
            dy = Dy[sprite->dir] * speed;

        } else {

            dx = Dx[sprite->dir] * speed;
            dy = Dy[sprite->dir] * speed;

            tx = (sprite->x + sprite->xHot) >>4;
            ty = (sprite->y + sprite->yHot) >>4;

            /* drift into the right lane */
            switch (sprite->dir) {

                  case 0: /* up */

                    z = ((tx <<4) + 4) - (sprite->x + sprite->xHot);

                    if (z < 0) {
                        dx = -1;
                    } else if (z > 0) {
                        dx = 1;
                    }

#ifdef DEBUGBUS
                    printf("moving up x %x z %d dx %d\n", sprite->x + sprite->xHot, z, dx);
#endif

                    break;

                case 1: /* right */

                    z = ((ty <<4) + 4) - (sprite->y + sprite->yHot);

                    if (z < 0) {
                        dy = -1;
                    } else if (z > 0) {
                        dy = 1;
                    }

#ifdef DEBUGBUS
                    printf("moving right y %x z %d dy %d\n", sprite->y + sprite->yHot, z, dy);
#endif

                    break;

                case 2: /* down */

                    z = (tx <<4) - (sprite->x + sprite->xHot);

                    if (z < 0) {
                        dx = -1;
                    } else if (z > 0) {
                        dx = 1;
                    }

#ifdef DEBUGBUS
                    printf("moving down x %x z %d dx %d\n", sprite->x + sprite->xHot, z, dx);
#endif

                    break;

                case 3: /* left */

                    z = (ty <<4) - (sprite->y + sprite->yHot);

                    if (z < 0) {
                        dy = -1;
                    } else if (z > 0) {
                        dy = 1;
                    }

#ifdef DEBUGBUS
                    printf("moving left y %x z %d dy %d\n", sprite->y + sprite->yHot, z, dy);
#endif

                    break;
            }
        }
    }

#ifdef DEBUGBUS
    printf("speed dx %d dy %d\n", dx, dy);
#endif

#define AHEAD 8

    otx = (sprite->x + sprite->xHot + (Dx[sprite->dir] * AHEAD)) >>4;
    oty = (sprite->y + sprite->yHot + (Dy[sprite->dir] * AHEAD)) >>4;

    otx = clamp(otx, 0, WORLD_W - 1);
    oty = clamp(oty, 0, WORLD_H - 1);

    tx = (sprite->x + sprite->xHot + dx + (Dx[sprite->dir] * AHEAD)) >>4;
    ty = (sprite->y + sprite->yHot + dy + (Dy[sprite->dir] * AHEAD)) >>4;

    tx = clamp(tx, 0, WORLD_W - 1);
    ty = clamp(ty, 0, WORLD_H - 1);

    if (tx != otx || ty != oty) {

#ifdef DEBUGBUS
        printf("drive from tile %d %d to %d %d\n",
               otx, oty, tx, ty);
#endif

        z = canDriveOn(tx, ty);

        if (z == 0) {

            /* can't drive forward into a new tile */
            if (speed == 8) {
                bulldozerTool(tx, ty);
            } else {
            }

        } else {

            /* drive forward into a new tile */
            if (z > 0) {
                /* smooth */
            } else {
                /* bumpy */
                dx /= 2;
                dy /= 2;
            }

        }
    }

    tx = (sprite->x + sprite->xHot + dx) >>4;
    ty = (sprite->y + sprite->yHot + dy) >>4;

    z = canDriveOn(tx, ty);

    if (z > 0) {
        /* cool, cruise along */
    } else {
        if (z < 0) {
            /* bumpy */
        } else {
            /* something in the way */
        }
    }

    sprite->x += dx;
    sprite->y += dy;

    if (enableDisasters) {
        SimSprite *s;
        int explode = 0;

        for (s = spriteList; s != NULL; s = s->next) {
            if (sprite != s && s->frame != 0
                    && (s->type == SPRITE_BUS
                        || (s->type == SPRITE_TRAIN && s->frame != 5))
                    && checkSpriteCollision(sprite, s)) {
                explodeSprite(s);
                explode = 1;
            }
        }

        if (explode) {
            explodeSprite(sprite);
        }

    }
}


/**
 * Can one drive at the specified tile?
 * @param x X coordinate at map.
 * @param y Y coordinate at map.
 * @return 0 if not, 1 if you can, -1 otherwise
 */
int Micropolis::canDriveOn(int x, int y)
{
    int tile;

    if (!testBounds(x, y)) {
        return 0;
    }

    tile = map[x][y] & LOMASK;

    if ((tile >= ROADBASE && tile <= LASTROAD && tile != BRWH && tile != BRWV)
              || tile == HRAILROAD || tile == VRAILROAD) {
        return 1;
    }

    if (tile == DIRT || tally(tile)) {
        return -1;
    }

    return 0;
}


/**
 * Handle explosion of sprite (mostly due to collision?).
 * @param sprite that should explode.
 * @todo Add a 'bus crashed' message to #MessageNumber.
 */
void Micropolis::explodeSprite(SimSprite *sprite)
{
    int x, y;

    sprite->frame = 0;

    x = sprite->x + sprite->xHot;
    y = sprite->y + sprite->yHot;
    makeExplosionAt(x, y);

    x = (x >>4);
    y = (y >>4);

    switch (sprite->type) {

        case SPRITE_AIRPLANE:
            sendMessage(MESSAGE_PLANE_CRASHED, x, y, true);
            break;

        case SPRITE_SHIP:
            sendMessage(MESSAGE_SHIP_CRASHED, x, y, true);
            break;

        case SPRITE_TRAIN:
            sendMessage(MESSAGE_TRAIN_CRASHED, x, y, true);
            break;

        case SPRITE_HELICOPTER:
            sendMessage(MESSAGE_HELICOPTER_CRASHED, x, y, true);
            break;

        case SPRITE_BUS:
            sendMessage(MESSAGE_TRAIN_CRASHED, x, y, true); /* XXX for now */
            break;

    }

    // Convert sprite coordinates to tile coordinates.
    makeSound("city", "ExplosionHigh", x, y); /* explosion */

    return;
}


bool Micropolis::checkWet(int x)
{
    if (x == HPOWER || x == VPOWER || x == HRAIL || x == VRAIL
              || x == BRWH || x == BRWV) {
        return true;
    } else {
        return false;
    }
}


/**
 * Destroy a map tile.
 * @param ox X coordinate in pixels.
 * @param oy Y coordinate in pixels.
 */
void Micropolis::destroyMapTile(int ox, int oy)
{
    short t, z, x, y;

    x = ox >>4;
    y = oy >>4;

    if (!testBounds(x, y)) {
        return;
    }

    z = map[x][y];
    t = z & LOMASK;

    if (t >= TREEBASE) {
        if (!(z & BURNBIT)) {

          if (t >= ROADBASE && t <= LASTROAD) {
              map[x][y] = RIVER;
          }

          return;
        }

        if (z & ZONEBIT) {

            startFireInZone(x, y, z);

            if (t > RZB) {
                makeExplosionAt(ox, oy);
            }

        }

        if (checkWet(t)) {
            map[x][y] = RIVER;
        } else {
            map[x][y] = (doAnimation ? TINYEXP : (LASTTINYEXP - 3))
                      | BULLBIT | ANIMBIT;
        }
    }
}


/**
 * Start a fire in a zone.
 * @param Xloc X coordinate in map coordinate.
 * @param Yloc Y coordinate in map coordinate.
 * @param ch   Map character at (\a Xloc, \a Yloc).
 */
void Micropolis::startFireInZone(int Xloc, int Yloc, int ch)
{
    short Xtem, Ytem;
    short x, y, XYmax;

    int value = rateOfGrowthMap.worldGet(Xloc, Yloc);
    value = clamp(value - 20, -200, 200);
    rateOfGrowthMap.worldSet(Xloc, Yloc, value);

    ch &= LOMASK;

    if (ch < PORTBASE) {
        XYmax = 2;
    } else {
        if (ch == AIRPORT) {
            XYmax = 5;
        } else {
            XYmax = 4;
        }
    }

    for (x = -1; x < XYmax; x++) {
        for (y = -1; y < XYmax; y++) {

            Xtem = Xloc + x;
            Ytem = Yloc + y;

            if (testBounds(Xtem, Ytem) && (map[Xtem][Ytem] & LOMASK) >= ROADBASE) {
                map[Xtem][Ytem] |= BULLBIT;
            }

        }
    }
}


/**
 * Start a fire at a single tile.
 * @param x X coordinate in map coordinate.
 * @param y Y coordinate in map coordinate.
 */
void Micropolis::startFire(int x, int y)
{
    int t, z;

    x >>= 4;
    y >>= 4;

    if (!testBounds(x, y)) {
        return;
    }

    z = map[x][y];
    t = z & LOMASK;

    if (!(z & BURNBIT) && t != DIRT) {
        return;
    }

    if (z & ZONEBIT) {
        return;
    }

    map[x][y] = randomFire();
}


/**
 * Try to start a new train sprite at the given map tile.
 * @param x X coordinate in map coordinate.
 * @param y Y coordinate in map coordinate.
 */
void Micropolis::generateTrain(int x, int y)
{
    if (totalPop > 20 && getSprite(SPRITE_TRAIN) == NULL && getRandom(25) == 0) {
        makeSprite(SPRITE_TRAIN, (x <<4) + TRA_GROOVE_X, (y <<4) + TRA_GROOVE_Y);
    }
}


/**
 * Try to start a new bus sprite at the given map tile.
 * @param x X coordinate in map coordinate.
 * @param y Y coordinate in map coordinate.
 */
void Micropolis::generateBus(int x, int y)
{
    if (getSprite(SPRITE_BUS) == NULL && getRandom(25) == 0) {
        makeSprite(SPRITE_BUS, (x <<4) + BUS_GROOVE_X, (y <<4) + BUS_GROOVE_Y);
    }
}


/** Try to construct a new ship sprite */
void Micropolis::generateShip()
{
    short x, y;

    if (!(getRandom16() & 3)) {
        for (x = 4; x < WORLD_W - 2; x++) {
            if (map[x][0] == CHANNEL)  {
                makeShipHere(x, 0);
                return;
            }
        }
    }

    if (!(getRandom16() & 3)) {
        for (y = 1; y < WORLD_H - 2; y++) {
            if (map[0][y] == CHANNEL)  {
                makeShipHere(0, y);
                return;
            }
        }
    }

    if (!(getRandom16() & 3)) {
        for (x = 4; x < WORLD_W - 2; x++) {
            if (map[x][WORLD_H - 1] == CHANNEL)  {
                makeShipHere(x, WORLD_H - 1);
                return;
            }
        }
    }

    if (!(getRandom16() & 3)) {
        for (y = 1; y < WORLD_H - 2; y++) {
            if (map[WORLD_W - 1][y] == CHANNEL)  {
                makeShipHere(WORLD_W - 1, y);
                return;
            }
        }
    }
}


/**
 * Start a new ship sprite at the given map tile.
 * @param x X coordinate in map coordinate.
 * @param y Y coordinate in map coordinate.
 */
void Micropolis::makeShipHere(int x, int y)
{
    makeSprite(SPRITE_SHIP, (x <<4) - (48 - 1), (y <<4));
}


/**
 * Start a new monster sprite.
 * @todo Make monster over land, because it disappears if it's made over water.
 *       Better yet make monster not disappear for a while after it's created,
 *       over land or water. Should never disappear prematurely.
 */
void Micropolis::makeMonster()
{
    int x, y, z, done = 0;
    SimSprite *sprite;

    sprite = getSprite(SPRITE_MONSTER);
    if (sprite != NULL) {
        sprite->soundCount = 1;
        sprite->count = 1000;
        sprite->destX = pollutionMaxX <<4;
        sprite->destY = pollutionMaxY <<4;
        return;
    }

    for (z = 0; z < 300; z++)  {

        x = getRandom(WORLD_W - 20) + 10;
        y = getRandom(WORLD_H - 10) + 5;

        if (map[x][y] == RIVER || map[x][y] == RIVER + BULLBIT) {
            makeMonsterAt(x, y);
            done = 1;
            break;
        }

    }

    if (!done) {
        makeMonsterAt(60, 50);
    }

}


/**
 * Start a new monster sprite at the given map tile.
 * @param x X coordinate in map coordinate.
 * @param y Y coordinate in map coordinate.
 */
void Micropolis::makeMonsterAt(int x, int y)
{
    makeSprite(SPRITE_MONSTER, (x << 4) + 48, (y << 4));
    sendMessage(MESSAGE_MONSTER_SIGHTED, x + 5, y, true, true);
}


/**
 * Ensure a helicopter sprite exists.
 *
 * If it does not exist, create one at the given coordinates.
 * @param pos Start position in map coordinates.
 */
void Micropolis::generateCopter(const Position &pos)
{
    if (getSprite(SPRITE_HELICOPTER) != NULL) {
        return;
    }

    makeSprite(SPRITE_HELICOPTER, (pos.posX << 4), (pos.posY << 4) + 30);
}


/**
 * Ensure an airplane sprite exists.
 *
 * If it does not exist, create one at the given coordinates.
 * @param pos Start position in map coordinates.
 */
void Micropolis::generatePlane(const Position &pos)
{
    if (getSprite(SPRITE_AIRPLANE) != NULL) {
        return;
    }

    makeSprite(SPRITE_AIRPLANE, (pos.posX <<4) + 48, (pos.posY <<4) + 12);
}


/** Ensure a tornado sprite exists. */
void Micropolis::makeTornado()
{
    short x, y;
    SimSprite *sprite;

    sprite = getSprite(SPRITE_TORNADO);
    if (sprite != NULL) {
        sprite->count = 200;
        return;
    }

    x = getRandom((WORLD_W <<4) - 800) + 400;
    y = getRandom((WORLD_H <<4) - 200) + 100;

    makeSprite(SPRITE_TORNADO, x, y);
    sendMessage(MESSAGE_TORNADO_SIGHTED, (x >>4) + 3, (y >>4) + 2, true, true);
}


/**
 * Construct an explosion sprite.
 * @param x X coordinate of the explosion (in map coordinates).
 * @param y Y coordinate of the explosion (in map coordinates).
 */
void Micropolis::makeExplosion(int x, int y)
{
    if (testBounds(x, y)) {
        makeExplosionAt((x << 4) + 8, (y << 4) + 8);
    }
}


/**
 * Construct an explosion sprite.
 * @param x X coordinate of the explosion (in pixels).
 * @param y Y coordinate of the explosion (in pixels).
 */
void Micropolis::makeExplosionAt( int x, int y)
{
    newSprite("", SPRITE_EXPLOSION, x - 40, y - 16);
}


////////////////////////////////////////////////////////////////////////