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# raycasting.cpp Example File
demos/embedded/raycasting/raycasting.cpp

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     #include <QtCore>
     #include <QtGui>

     #include <math.h>

     #ifndef M_PI
     #define M_PI 3.14159265358979323846
     #endif

     #define WORLD_SIZE 8
     int world_map[WORLD_SIZE][WORLD_SIZE] = {
         { 1, 1, 1, 1, 6, 1, 1, 1 },
         { 1, 0, 0, 1, 0, 0, 0, 7 },
         { 1, 1, 0, 1, 0, 1, 1, 1 },
         { 6, 0, 0, 0, 0, 0, 0, 3 },
         { 1, 8, 8, 0, 8, 0, 8, 1 },
         { 2, 2, 0, 0, 8, 8, 7, 1 },
         { 3, 0, 0, 0, 0, 0, 0, 5 },
         { 2, 2, 2, 2, 7, 4, 4, 4 },
     };

     #define TEXTURE_SIZE 64
     #define TEXTURE_BLOCK (TEXTURE_SIZE * TEXTURE_SIZE)

     class Raycasting: public QWidget
     {
     public:
         Raycasting(QWidget *parent = 0)
                 : QWidget(parent)
                 , angle(0.5)
                 , playerPos(1.5, 1.5)
                 , angleDelta(0)
                 , moveDelta(0)
                 , touchDevice(false) {

             // http://www.areyep.com/RIPandMCS-TextureLibrary.html
             textureImg.load(":/textures.png");
             textureImg = textureImg.convertToFormat(QImage::Format_ARGB32);
             Q_ASSERT(textureImg.width() == TEXTURE_SIZE * 2);
             Q_ASSERT(textureImg.bytesPerLine() == 4 * TEXTURE_SIZE * 2);
             textureCount = textureImg.height() / TEXTURE_SIZE;

             watch.start();
             ticker.start(25, this);
             setAttribute(Qt::WA_OpaquePaintEvent, true);
             setMouseTracking(false);
         }

         void updatePlayer() {
             int interval = qBound(20, watch.elapsed(), 250);
             watch.start();
             angle += angleDelta * interval / 1000;
             qreal step = moveDelta * interval / 1000;
             qreal dx = cos(angle) * step;
             qreal dy = sin(angle) * step;
             QPointF pos = playerPos + 3 * QPointF(dx, dy);
             int xi = static_cast<int>(pos.x());
             int yi = static_cast<int>(pos.y());
             if (world_map[yi][xi] == 0)
                 playerPos = playerPos + QPointF(dx, dy);
         }

         void showFps() {
             static QTime frameTick;
             static int totalFrame = 0;
             if (!(totalFrame & 31)) {
                 int elapsed = frameTick.elapsed();
                 frameTick.start();
                 int fps = 32 * 1000 / (1 + elapsed);
                 setWindowTitle(QString("Raycasting (%1 FPS)").arg(fps));
             }
             totalFrame++;
         }

         void render() {

             // setup the screen surface
             if (buffer.size() != bufferSize)
                 buffer = QImage(bufferSize, QImage::Format_ARGB32);
             int bufw = buffer.width();
             int bufh = buffer.height();
             if (bufw <= 0 || bufh <= 0)
                 return;

             // we intentionally cheat here, to avoid detach
             const uchar *ptr = buffer.bits();
             QRgb *start = (QRgb*)(ptr);
             QRgb stride = buffer.bytesPerLine() / 4;
             QRgb *finish = start + stride * bufh;

             // prepare the texture pointer
             const uchar *src = textureImg.bits();
             const QRgb *texsrc = reinterpret_cast<const QRgb*>(src);

             // cast all rays here
             qreal sina = sin(angle);
             qreal cosa = cos(angle);
             qreal u = cosa - sina;
             qreal v = sina + cosa;
             qreal du = 2 * sina / bufw;
             qreal dv = -2 * cosa / bufw;

             for (int ray = 0; ray < bufw; ++ray, u += du, v += dv) {
                 // everytime this ray advances 'u' units in x direction,
                 // it also advanced 'v' units in y direction
                 qreal uu = (u < 0) ? -u : u;
                 qreal vv = (v < 0) ? -v : v;
                 qreal duu = 1 / uu;
                 qreal dvv = 1 / vv;
                 int stepx = (u < 0) ? -1 : 1;
                 int stepy = (v < 0) ? -1 : 1;

                 // the cell in the map that we need to check
                 qreal px = playerPos.x();
                 qreal py = playerPos.y();
                 int mapx = static_cast<int>(px);
                 int mapy = static_cast<int>(py);

                 // the position and texture for the hit
                 int texture = 0;
                 qreal hitdist = 0.1;
                 qreal texofs = 0;
                 bool dark = false;

                 // first hit at constant x and constant y lines
                 qreal distx = (u > 0) ? (mapx + 1 - px) * duu : (px - mapx) * duu;
                 qreal disty = (v > 0) ? (mapy + 1 - py) * dvv : (py - mapy) * dvv;

                 // loop until we hit something
                 while (texture <= 0) {
                     if (distx > disty) {
                         // shorter distance to a hit in constant y line
                         hitdist = disty;
                         disty += dvv;
                         mapy += stepy;
                         texture = world_map[mapy][mapx];
                         if (texture > 0) {
                             dark = true;
                             if (stepy > 0) {
                                 qreal ofs = px + u * (mapy - py) / v;
                                 texofs = ofs - floor(ofs);
                             } else {
                                 qreal ofs = px + u * (mapy + 1 - py) / v;
                                 texofs = ofs - floor(ofs);
                             }
                         }
                     } else {
                         // shorter distance to a hit in constant x line
                         hitdist = distx;
                         distx += duu;
                         mapx += stepx;
                         texture = world_map[mapy][mapx];
                         if (texture > 0) {
                             if (stepx > 0) {
                                 qreal ofs = py + v * (mapx - px) / u;
                                 texofs = ofs - floor(ofs);
                             } else {
                                 qreal ofs = py + v * (mapx + 1 - px) / u;
                                 texofs = ceil(ofs) - ofs;
                             }
                         }
                     }
                 }

                 // get the texture, note that the texture image
                 // has two textures horizontally, "normal" vs "dark"
                 int col = static_cast<int>(texofs * TEXTURE_SIZE);
                 col = qBound(0, col, TEXTURE_SIZE - 1);
                 texture = (texture - 1) % textureCount;
                 const QRgb *tex = texsrc + TEXTURE_BLOCK * texture * 2 +
                                   (TEXTURE_SIZE * 2 * col);
                 if (dark)
                     tex += TEXTURE_SIZE;

                 // start from the texture center (horizontally)
                 int h = static_cast<int>(bufw / hitdist / 2);
                 int dy = (TEXTURE_SIZE << 12) / h;
                 int p1 = ((TEXTURE_SIZE / 2) << 12) - dy;
                 int p2 = p1 + dy;

                 // start from the screen center (vertically)
                 // y1 will go up (decrease), y2 will go down (increase)
                 int y1 = bufh / 2;
                 int y2 = y1 + 1;
                 QRgb *pixel1 = start + y1 * stride + ray;
                 QRgb *pixel2 = pixel1 + stride;

                 // map the texture to the sliver
                 while (y1 >= 0 && y2 < bufh && p1 >= 0) {
                     *pixel1 = tex[p1 >> 12];
                     *pixel2 = tex[p2 >> 12];
                     p1 -= dy;
                     p2 += dy;
                     --y1;
                     ++y2;
                     pixel1 -= stride;
                     pixel2 += stride;
                 }

                 // ceiling and floor
                 for (; pixel1 > start; pixel1 -= stride)
                     *pixel1 = qRgb(0, 0, 0);
                 for (; pixel2 < finish; pixel2 += stride)
                     *pixel2 = qRgb(96, 96, 96);
             }

             update(QRect(QPoint(0, 0), bufferSize));
         }

     protected:

         void resizeEvent(QResizeEvent*) {
     #if defined(Q_OS_WINCE_WM)
             touchDevice = true;
     #elif defined(Q_OS_SYMBIAN)
             // FIXME: use HAL
             if (width() > 480 || height() > 480)
                 touchDevice = true;
     #else
             touchDevice = false;
     #endif
             if (touchDevice) {
                 if (width() < height()) {
                     trackPad = QRect(0, height() / 2, width(), height() / 2);
                     centerPad = QPoint(width() / 2, height() * 3 / 4);
                     bufferSize = QSize(width(), height() / 2);
                 } else {
                     trackPad = QRect(width() / 2, 0, width() / 2, height());
                     centerPad = QPoint(width() * 3 / 4, height() / 2);
                     bufferSize = QSize(width() / 2, height());
                 }
             } else {
                 trackPad = QRect();
                 bufferSize = size();
             }
             update();
        }

         void timerEvent(QTimerEvent*) {
             updatePlayer();
             render();
             showFps();
         }

         void paintEvent(QPaintEvent *event) {
             QPainter p(this);
             p.setCompositionMode(QPainter::CompositionMode_Source);

             p.drawImage(event->rect(), buffer, event->rect());

             if (touchDevice && event->rect().intersects(trackPad)) {
                 p.fillRect(trackPad, Qt::white);
                 p.setPen(QPen(QColor(224, 224, 224), 6));
                 int rad = qMin(trackPad.width(), trackPad.height()) * 0.3;
                 p.drawEllipse(centerPad, rad, rad);

                 p.setPen(Qt::NoPen);
                 p.setBrush(Qt::gray);

                 QPolygon poly;
                 poly << QPoint(-30, 0);
                 poly << QPoint(0, -40);
                 poly << QPoint(30, 0);

                 p.translate(centerPad);
                 for (int i = 0; i < 4; ++i) {
                     p.rotate(90);
                     p.translate(0, 20 - rad);
                     p.drawPolygon(poly);
                     p.translate(0, rad - 20);
                 }
             }

             p.end();
         }

         void keyPressEvent(QKeyEvent *event) {
             event->accept();
             if (event->key() == Qt::Key_Left)
                 angleDelta = 1.3 * M_PI;
             if (event->key() == Qt::Key_Right)
                 angleDelta = -1.3 * M_PI;
             if (event->key() == Qt::Key_Up)
                 moveDelta = 2.5;
             if (event->key() == Qt::Key_Down)
                 moveDelta = -2.5;
         }

         void keyReleaseEvent(QKeyEvent *event) {
             event->accept();
             if (event->key() == Qt::Key_Left)
                 angleDelta = (angleDelta > 0) ? 0 : angleDelta;
             if (event->key() == Qt::Key_Right)
                 angleDelta = (angleDelta < 0) ? 0 : angleDelta;
             if (event->key() == Qt::Key_Up)
                 moveDelta = (moveDelta > 0) ? 0 : moveDelta;
             if (event->key() == Qt::Key_Down)
                 moveDelta = (moveDelta < 0) ? 0 : moveDelta;
         }

         void mousePressEvent(QMouseEvent *event) {
             qreal dx = centerPad.x() - event->pos().x();
             qreal dy = centerPad.y() - event->pos().y();
             angleDelta = dx * 2 * M_PI / width();
             moveDelta = dy * 10 / height();
         }

         void mouseMoveEvent(QMouseEvent *event) {
             qreal dx = centerPad.x() - event->pos().x();
             qreal dy = centerPad.y() - event->pos().y();
             angleDelta = dx * 2 * M_PI / width();
             moveDelta = dy * 10 / height();
         }

         void mouseReleaseEvent(QMouseEvent*) {
             angleDelta = 0;
             moveDelta = 0;
         }

     private:
         QTime watch;
         QBasicTimer ticker;
         QImage buffer;
         qreal angle;
         QPointF playerPos;
         qreal angleDelta;
         qreal moveDelta;
         QImage textureImg;
         int textureCount;
         bool touchDevice;
         QRect trackPad;
         QPoint centerPad;
         QSize bufferSize;
     };

     int main(int argc, char **argv)
     {
         QApplication app(argc, argv);

         Raycasting w;
         w.setWindowTitle("Raycasting");
     #if defined(Q_OS_SYMBIAN) || defined(Q_OS_WINCE_WM)
         w.showMaximized();
     #else
         w.resize(640, 480);
         w.show();
     #endif

         return app.exec();
     }