[Qt] Added viewport mode

Qt Quick requires third-party rendering codes to follow its standards
with regards to viewport transform. Qt 5.6 adds a 'mirrorVertically'
property but that only solves the solution for that version of Qt
onwards. Telling Mapbox GL core to flip the Y axis makes QQuickMapboxGL
item available for Qt 5.2 onwards.

Qt 'mirrorVertically' property documentation:
http://doc.qt.io/qt-5/qquickframebufferobject.html#mirrorVertically-prop

Fixes #4866.

1 files changed, 9 insertions, 0 deletions

diff --git a/platform/qt/include/qmapboxgl.hpp b/platform/qt/include/qmapboxgl.hpp
index 4c02c42736..3b10dadc9c 100644
--- a/platform/qt/include/qmapboxgl.hpp
+++ b/platform/qt/include/qmapboxgl.hpp
@@ -36,6 +36,11 @@ public:
         ConstrainWidthAndHeight
     };
 
+    enum ViewportMode {
+        DefaultViewport = 0,
+        FlippedYViewport
+    };
+
     MapMode mapMode() const;
     void setMapMode(MapMode);
 
@@ -45,6 +50,9 @@ public:
     ConstrainMode constrainMode() const;
     void setConstrainMode(ConstrainMode);
 
+    ViewportMode viewportMode() const;
+    void setViewportMode(ViewportMode);
+
     unsigned cacheDatabaseMaximumSize() const;
     void setCacheDatabaseMaximumSize(unsigned);
 
@@ -61,6 +69,7 @@ private:
     MapMode m_mapMode;
     GLContextMode m_contextMode;
     ConstrainMode m_constrainMode;
+    ViewportMode m_viewportMode;
 
     unsigned m_cacheMaximumSize;
     QString m_cacheDatabasePath;