[core] Added Map::pitchBy()

include/mbgl/map/map.hpp

@@ -90,6 +90,9 @@ public:
     void setLatLngZoom(const LatLng&, double zoom, const EdgeInsets&, const AnimationOptions& = {});
     void resetZoom();
 
+    // Pitch
+    void pitchBy(double pitch, const AnimationOptions& animation = {});
+
     // Bounds
     void setLatLngBounds(optional<LatLngBounds>);
     optional<LatLngBounds> getLatLngBounds() const;

platform/glfw/glfw_view.cpp

@@ -553,7 +553,7 @@ void GLFWView::onMouseMove(GLFWwindow *window, double x, double y) {
     } else if (view->pitching) {
         const double dy = y - view->lastY;
         if (dy) {
-            view->map->setPitch(view->map->getPitch() - dy / 2);
+            view->map->pitchBy(dy / 2);
         }
     }
     view->lastX = x;

platform/qt/app/mapwindow.cpp

@@ -437,7 +437,7 @@ void MapWindow::mouseMoveEvent(QMouseEvent *ev)
 
     if (!delta.isNull()) {
         if (ev->buttons() == Qt::LeftButton && ev->modifiers() & Qt::ShiftModifier) {
-            m_map->setPitch(m_map->pitch() - delta.y());
+            m_map->pitchBy(delta.y());
         } else if (ev->buttons() == Qt::LeftButton) {
             m_map->moveBy(delta);
         } else if (ev->buttons() == Qt::RightButton) {

platform/qt/include/qmapboxgl.hpp

@@ -182,6 +182,7 @@ public:
 
     double pitch() const;
     void setPitch(double pitch);
+    void pitchBy(double pitch);
 
     NorthOrientation northOrientation() const;
     void setNorthOrientation(NorthOrientation);

platform/qt/src/qmapboxgl.cpp

@@ -885,6 +885,11 @@ void QMapboxGL::setPitch(double pitch_)
     d_ptr->mapObj->setPitch(pitch_);
 }
 
+void QMapboxGL::pitchBy(double pitch_)
+{
+    d_ptr->mapObj->pitchBy(pitch_);
+}
+
 /*!
     Returns the north orientation mode.
 */

src/mbgl/map/map.cpp

@@ -317,6 +317,12 @@ void Map::resetZoom() {
     setZoom(0);
 }
 
+#pragma mark - Pitch
+
+void Map::pitchBy(double pitch, const AnimationOptions& animation) {
+    easeTo(CameraOptions().withPitch((impl->transform.getPitch() * util::RAD2DEG) - pitch), animation);
+}
+
 #pragma mark - Bounds
 
 optional<LatLngBounds> Map::getLatLngBounds() const {