6 files changed, 54 insertions, 15 deletions
diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index 0747606fc6..a4f9422184 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -34,7 +34,7 @@ enum class RenderState {
 
 class Map::Impl : public Style::Observer {
 public:
-    Impl(View&, FileSource&, MapMode, GLContextMode, ConstrainMode);
+    Impl(View&, FileSource&, MapMode, GLContextMode, ConstrainMode, ViewportMode);
 
     void onResourceLoaded() override;
     void onResourceError(std::exception_ptr) override;
@@ -76,16 +76,16 @@ public:
     bool loading = false;
 };
 
-Map::Map(View& view, FileSource& fileSource, MapMode mapMode, GLContextMode contextMode, ConstrainMode constrainMode)
-    : impl(std::make_unique<Impl>(view, fileSource, mapMode, contextMode, constrainMode)) {
+Map::Map(View& view, FileSource& fileSource, MapMode mapMode, GLContextMode contextMode, ConstrainMode constrainMode, ViewportMode viewportMode)
+    : impl(std::make_unique<Impl>(view, fileSource, mapMode, contextMode, constrainMode, viewportMode)) {
     view.initialize(this);
     update(Update::Dimensions);
 }
 
-Map::Impl::Impl(View& view_, FileSource& fileSource_, MapMode mode_, GLContextMode contextMode_, ConstrainMode constrainMode_)
+Map::Impl::Impl(View& view_, FileSource& fileSource_, MapMode mode_, GLContextMode contextMode_, ConstrainMode constrainMode_, ViewportMode viewportMode_)
     : view(view_),
       fileSource(fileSource_),
-      transform(view, constrainMode_),
+      transform(view, constrainMode_, viewportMode_),
       mode(mode_),
       contextMode(contextMode_),
       pixelRatio(view.getPixelRatio()),
@@ -638,6 +638,17 @@ ConstrainMode Map::getConstrainMode() const {
     return impl->transform.getConstrainMode();
 }
 
+#pragma mark - Viewport mode
+
+void Map::setViewportMode(mbgl::ViewportMode mode) {
+    impl->transform.setViewportMode(mode);
+    update(Update::Repaint);
+}
+
+ViewportMode Map::getViewportMode() const {
+    return impl->transform.getViewportMode();
+}
+
 #pragma mark - Projection
 
 double Map::getMetersPerPixelAtLatitude(double lat, double zoom) const {
diff --git a/src/mbgl/map/transform.cpp b/src/mbgl/map/transform.cpp
index 69a644c7d9..958f9d9b63 100644
--- a/src/mbgl/map/transform.cpp
+++ b/src/mbgl/map/transform.cpp
@@ -36,9 +36,9 @@ static double _normalizeAngle(double angle, double anchorAngle)
     return angle;
 }
 
-Transform::Transform(View &view_, ConstrainMode constrainMode)
+Transform::Transform(View &view_, ConstrainMode constrainMode, ViewportMode viewportMode)
     : view(view_)
-    , state(constrainMode)
+    , state(constrainMode, viewportMode)
 {
 }
 
@@ -555,6 +555,16 @@ ConstrainMode Transform::getConstrainMode() const {
     return state.getConstrainMode();
 }
 
+#pragma mark - Viewport mode
+
+void Transform::setViewportMode(mbgl::ViewportMode mode) {
+    state.viewportMode = mode;
+}
+
+ViewportMode Transform::getViewportMode() const {
+    return state.getViewportMode();
+}
+
 #pragma mark - Transition
 
 void Transform::startTransition(const CameraOptions& camera,
diff --git a/src/mbgl/map/transform.hpp b/src/mbgl/map/transform.hpp
index 7d3bdceb99..cd2d7a33f3 100644
--- a/src/mbgl/map/transform.hpp
+++ b/src/mbgl/map/transform.hpp
@@ -20,7 +20,7 @@ class View;
 
 class Transform : private util::noncopyable {
 public:
-    Transform(View&, ConstrainMode);
+    Transform(View&, ConstrainMode, ViewportMode);
 
     // Map view
     bool resize(std::array<uint16_t, 2> size);
@@ -132,11 +132,15 @@ public:
     // North Orientation
     void setNorthOrientation(NorthOrientation);
     NorthOrientation getNorthOrientation() const;
-    
+
     // Constrain mode
     void setConstrainMode(ConstrainMode);
     ConstrainMode getConstrainMode() const;
 
+    // Viewport mode
+    void setViewportMode(ViewportMode);
+    ViewportMode getViewportMode() const;
+
     // Transitions
     bool inTransition() const;
     Update updateTransitions(const TimePoint& now);
diff --git a/src/mbgl/map/transform_state.cpp b/src/mbgl/map/transform_state.cpp
index 2813d6334e..0b8d831e54 100644
--- a/src/mbgl/map/transform_state.cpp
+++ b/src/mbgl/map/transform_state.cpp
@@ -7,8 +7,9 @@
 
 namespace mbgl {
 
-TransformState::TransformState(ConstrainMode constrainMode_)
+TransformState::TransformState(ConstrainMode constrainMode_, ViewportMode viewportMode_)
     : constrainMode(constrainMode_)
+    , viewportMode(viewportMode_)
 {
 }
 
@@ -39,7 +40,8 @@ void TransformState::getProjMatrix(mat4& projMatrix) const {
 
     // After the rotateX, z values are in pixel units. Convert them to
     // altitude unites. 1 altitude unit = the screen height.
-    matrix::scale(projMatrix, projMatrix, 1, -1, 1.0f / (rotatedNorth() ? getWidth() : getHeight()));
+    const bool flippedY = viewportMode == ViewportMode::FlippedY;
+    matrix::scale(projMatrix, projMatrix, 1, flippedY ? 1 : -1, 1.0f / (rotatedNorth() ? getWidth() : getHeight()));
 
     using NO = NorthOrientation;
     switch (getNorthOrientation()) {
@@ -89,6 +91,12 @@ ConstrainMode TransformState::getConstrainMode() const {
     return constrainMode;
 }
 
+#pragma mark - ViewportMode
+
+ViewportMode TransformState::getViewportMode() const {
+    return viewportMode;
+}
+
 #pragma mark - Position
 
 LatLng TransformState::getLatLng(LatLng::WrapMode wrapMode) const {
diff --git a/src/mbgl/map/transform_state.hpp b/src/mbgl/map/transform_state.hpp
index b9acad66f1..970dda2613 100644
--- a/src/mbgl/map/transform_state.hpp
+++ b/src/mbgl/map/transform_state.hpp
@@ -18,7 +18,7 @@ class TransformState {
     friend class Transform;
 
 public:
-    TransformState(ConstrainMode = ConstrainMode::HeightOnly);
+    TransformState(ConstrainMode = ConstrainMode::HeightOnly, ViewportMode = ViewportMode::Default);
 
     // Matrix
     void matrixFor(mat4&, const UnwrappedTileID&) const;
@@ -31,10 +31,13 @@ public:
     // North Orientation
     NorthOrientation getNorthOrientation() const;
     double getNorthOrientationAngle() const;
-    
+
     // Constrain mode
     ConstrainMode getConstrainMode() const;
 
+    // Viewport mode
+    ViewportMode getViewportMode() const;
+
     // Position
     LatLng getLatLng(LatLng::WrapMode = LatLng::Unwrapped) const;
     double pixel_x() const;
@@ -99,6 +102,7 @@ private:
 
 private:
     ConstrainMode constrainMode;
+    ViewportMode viewportMode;
 
     // animation state
     bool rotating = false;
diff --git a/src/mbgl/renderer/painter_symbol.cpp b/src/mbgl/renderer/painter_symbol.cpp
index a48c70866c..42355493a5 100644
--- a/src/mbgl/renderer/painter_symbol.cpp
+++ b/src/mbgl/renderer/painter_symbol.cpp
@@ -51,7 +51,8 @@ void Painter::renderSDF(SymbolBucket &bucket,
         gammaScale = 1.0f;
         matrix::rotate_z(exMatrix, exMatrix, state.getNorthOrientationAngle());
     }
-    matrix::scale(exMatrix, exMatrix, s, s, 1);
+    const bool flippedY = !skewed && state.getViewportMode() == ViewportMode::FlippedY;
+    matrix::scale(exMatrix, exMatrix, s, flippedY ? -s : s, 1);
 
     // If layerStyle.size > bucket.info.fontSize then labels may collide
     float fontSize = paintSize;
@@ -217,7 +218,8 @@ void Painter::renderSymbol(SymbolBucket& bucket,
                 matrix::rotate_z(exMatrix, exMatrix, state.getNorthOrientationAngle());
                 s = state.getAltitude();
             }
-            matrix::scale(exMatrix, exMatrix, s, s, 1);
+            const bool flippedY = !skewed && state.getViewportMode() == ViewportMode::FlippedY;
+            matrix::scale(exMatrix, exMatrix, s, flippedY ? -s : s, 1);
 
             matrix::scale(exMatrix, exMatrix, fontScale, fontScale, 1.0f);