GmxPlugin: Support horizontal and vertical flipping

Flipping is now supported for tiles and tile objects (whether exported as
instances or as tiles).

Diagonal flipping remains unsupported for now. It could be supported for
tile objects exported as instances, by using the rotation.

src/plugins/gmx/gmxplugin.cpp

@@ -132,15 +132,26 @@ bool GmxPlugin::write(const Map *map, const QString &fileName)
                 // Tile objects have bottom-left origin in Tiled, so the
                 // position needs to be translated for top-left origin in
                 // GameMaker, taking into account the rotation.
-                QPointF origin(0, -object->height());
-                origin = QTransform().rotate(object->rotation()).map(origin);
-                pos += origin;
+                QTransform transform;
+                transform.rotate(object->rotation());
 
-                // For tile objects we can support scaling
+                pos += transform.map(QPointF(0, -object->height()));
+
+                // For tile objects we can support scaling and flipping, though
+                // flipping in combination with rotation doesn't work in GameMaker.
                 if (auto tile = object->cell().tile) {
                     const QSize tileSize = tile->size();
                     scaleX = object->width() / tileSize.width();
                     scaleY = object->height() / tileSize.height();
+
+                    if (object->cell().flippedHorizontally) {
+                        scaleX *= -1;
+                        pos += transform.map(QPointF(object->width(), 0));
+                    }
+                    if (object->cell().flippedVertically) {
+                        scaleY *= -1;
+                        pos += transform.map(QPointF(0, object->height()));
+                    }
                 }
             }
 
@@ -190,9 +201,23 @@ bool GmxPlugin::write(const Map *map, const QString &fileName)
 
                         stream.writeStartElement("tile");
 
+                        int pixelX = x * map->tileWidth();
+                        int pixelY = y * map->tileHeight();
+                        qreal scaleX = 1;
+                        qreal scaleY = 1;
+
+                        if (cell.flippedHorizontally) {
+                            scaleX = -1;
+                            pixelX += tile->width();
+                        }
+                        if (cell.flippedVertically) {
+                            scaleY = -1;
+                            pixelY += tile->height();
+                        }
+
                         stream.writeAttribute("bgName", tileset->name());
-                        stream.writeAttribute("x", QString::number(x * map->tileWidth()));
-                        stream.writeAttribute("y", QString::number(y * map->tileHeight()));
+                        stream.writeAttribute("x", QString::number(pixelX));
+                        stream.writeAttribute("y", QString::number(pixelY));
                         stream.writeAttribute("w", QString::number(tile->width()));
                         stream.writeAttribute("h", QString::number(tile->height()));
 
@@ -204,6 +229,9 @@ bool GmxPlugin::write(const Map *map, const QString &fileName)
                         stream.writeAttribute("id", QString::number(++tileId));
                         stream.writeAttribute("depth", depth);
 
+                        stream.writeAttribute("scaleX", QString::number(scaleX));
+                        stream.writeAttribute("scaleY", QString::number(scaleY));
+
                         stream.writeEndElement();
                     }
                 }
@@ -232,14 +260,25 @@ bool GmxPlugin::write(const Map *map, const QString &fileName)
                     const Tileset *tileset = tile->tileset();
 
                     const QSize tileSize = tile->size();
-                    const qreal scaleX = object->width() / tileSize.width();
-                    const qreal scaleY = object->height() / tileSize.height();
+                    qreal scaleX = object->width() / tileSize.width();
+                    qreal scaleY = object->height() / tileSize.height();
+                    qreal x = object->x();
+                    qreal y = object->y() - object->height();
+
+                    if (object->cell().flippedHorizontally) {
+                        scaleX *= -1;
+                        x += object->width();
+                    }
+                    if (object->cell().flippedVertically) {
+                        scaleY *= -1;
+                        y += object->height();
+                    }
 
                     stream.writeStartElement("tile");
 
                     stream.writeAttribute("bgName", tileset->name());
-                    stream.writeAttribute("x", QString::number(qRound(object->x())));
-                    stream.writeAttribute("y", QString::number(qRound(object->y() - object->height())));
+                    stream.writeAttribute("x", QString::number(qRound(x)));
+                    stream.writeAttribute("y", QString::number(qRound(y)));
                     stream.writeAttribute("w", QString::number(tile->width()));
                     stream.writeAttribute("h", QString::number(tile->height()));