[Qt] Add a Qt app example

Should build and run with `make run-qt`

Signed-off-by: Bruno Abinader <bruno@mapbox.com>
Signed-off-by: Thiago Marcos P. Santos <thiago@mapbox.com>

platform/qt/app/main.cpp

@@ -0,0 +1,20 @@
+#include "mapwindow.hpp"
+
+#include <QApplication>
+
+int main(int argc, char **argv)
+{
+    QApplication app(argc, argv);
+
+    QMapboxGLSettings settings;
+    settings.setAccessToken(qgetenv("MAPBOX_ACCESS_TOKEN"));
+    settings.setCacheDatabasePath("/tmp/mbgl-cache.db");
+    settings.setCacheDatabaseMaximumSize(20 * 1024 * 1024);
+
+    MapWindow window(settings);
+
+    window.resize(800, 600);
+    window.show();
+
+    return app.exec();
+}

platform/qt/app/mapwindow.cpp

@@ -0,0 +1,122 @@
+#include "mapwindow.hpp"
+
+#include <mbgl/util/default_styles.hpp>
+
+#include <QKeyEvent>
+#include <QMouseEvent>
+#include <QString>
+
+MapWindow::MapWindow(const QMapboxGLSettings &settings) : m_map(nullptr, settings)
+{
+    connect(&m_map, SIGNAL(needsRendering()), this, SLOT(updateGL()));
+
+    // Set default location to Helsinki.
+    m_map.setCoordinateZoom(QMapboxGL::Coordinate(60.170448, 24.942046), 14);
+
+    changeStyle();
+}
+
+void MapWindow::changeStyle()
+{
+    static uint8_t currentStyleIndex;
+
+    mbgl::util::default_styles::DefaultStyle newStyle =
+        mbgl::util::default_styles::orderedStyles[currentStyleIndex];
+
+    QString url(newStyle.url);
+    m_map.setStyleURL(url);
+
+    QString name(newStyle.name);
+    setWindowTitle(QString("Mapbox GL: ") + name);
+
+    if (++currentStyleIndex == mbgl::util::default_styles::numOrderedStyles) {
+        currentStyleIndex = 0;
+    }
+}
+
+void MapWindow::keyPressEvent(QKeyEvent *ev)
+{
+    if (ev->key() == Qt::Key_S) {
+        changeStyle();
+    }
+
+    ev->accept();
+}
+
+void MapWindow::mousePressEvent(QMouseEvent *ev)
+{
+#if QT_VERSION < 0x050000
+    m_lastPos = ev->posF();
+#else
+    m_lastPos = ev->localPos();
+#endif
+
+    if (ev->type() == QEvent::MouseButtonPress) {
+        if (ev->buttons() == (Qt::LeftButton | Qt::RightButton)) {
+            changeStyle();
+        }
+    }
+
+    if (ev->type() == QEvent::MouseButtonDblClick) {
+        if (ev->buttons() == Qt::LeftButton) {
+            m_map.scaleBy(2.0, m_lastPos, 500);
+        } else if (ev->buttons() == Qt::RightButton) {
+            m_map.scaleBy(0.5, m_lastPos, 500);
+        }
+    }
+
+    ev->accept();
+}
+
+void MapWindow::mouseMoveEvent(QMouseEvent *ev)
+{
+#if QT_VERSION < 0x050000
+    QPointF delta = ev->posF() - m_lastPos;
+#else
+    QPointF delta = ev->localPos() - m_lastPos;
+#endif
+
+    if (!delta.isNull()) {
+        if (ev->buttons() == Qt::LeftButton) {
+            m_map.moveBy(delta);
+        } else if (ev->buttons() == Qt::RightButton) {
+#if QT_VERSION < 0x050000
+            m_map.rotateBy(m_lastPos, ev->posF());
+#else
+            m_map.rotateBy(m_lastPos, ev->localPos());
+#endif
+        }
+    }
+
+#if QT_VERSION < 0x050000
+    m_lastPos = ev->posF();
+#else
+    m_lastPos = ev->localPos();
+#endif
+    ev->accept();
+}
+
+void MapWindow::wheelEvent(QWheelEvent *ev)
+{
+    if (ev->orientation() == Qt::Horizontal) {
+        return;
+    }
+
+    float factor = ev->delta() / 1200.;
+    if (ev->delta() < 0) {
+        factor = factor > -1 ? factor : 1 / factor;
+    }
+
+    m_map.scaleBy(1 + factor, ev->pos(), 50);
+    ev->accept();
+}
+
+void MapWindow::resizeGL(int w, int h)
+{
+    m_map.resize(QSize(w, h));
+}
+
+void MapWindow::paintGL()
+{
+    m_map.render();
+}

platform/qt/app/mapwindow.hpp

@@ -0,0 +1,32 @@
+#ifndef MAPWINDOW_H
+#define MAPWINDOW_H
+
+#include <QGLWidget>
+#include <QMapboxGL>
+
+class QKeyEvent;
+class QMouseEvent;
+class QWheelEvent;
+
+class MapWindow : public QGLWidget
+{
+public:
+    MapWindow(const QMapboxGLSettings &);
+
+private:
+    void changeStyle();
+
+    // QGLWidget implementation.
+    void keyPressEvent(QKeyEvent *ev) final;
+    void mousePressEvent(QMouseEvent *ev) final;
+    void mouseMoveEvent(QMouseEvent *ev) final;
+    void wheelEvent(QWheelEvent *ev) final;
+    void resizeGL(int w, int h) final;
+    void paintGL() final;
+
+    QPointF m_lastPos;
+
+    QMapboxGL m_map;
+};
+
+#endif