Fix dragging items out of map bounds

In 5.9.0 map items are clipped against the visible region.
This implies that their geometry is also clipped against
the visible region.
This is problematic in ::geometryChanged, since the old
geometry is always clipped in this way.

This patch clips items against a "projectable" region
instead, that is the part of the map that is in front
of the camera.

Since this can produce very large vertices, mapbox
earcut 3rd party library is pulled in, to replace
qTriangulate that only supports coordinates up to
1<<21.

Task-number: QTBUG-61727
Change-Id: I7449e755a4848a2b2107c5de4e27821e3e887bfb
Reviewed-by: Paolo Angelelli <paolo.angelelli@qt.io>

1 files changed, 52 insertions, 5 deletions

diff --git a/src/location/maps/qgeoprojection.cpp b/src/location/maps/qgeoprojection.cpp
index 07747a31..609fb934 100644
--- a/src/location/maps/qgeoprojection.cpp
+++ b/src/location/maps/qgeoprojection.cpp
@@ -317,6 +317,13 @@ QList<QDoubleVector2D> QGeoProjectionWebMercator::visibleRegion() const
     return m_visibleRegion;
 }
 
+QList<QDoubleVector2D> QGeoProjectionWebMercator::projectableRegion() const
+{
+    if (m_visibleRegionDirty)
+        const_cast<QGeoProjectionWebMercator *>(this)->updateVisibleRegion();
+    return m_projectableRegion;
+}
+
 QDoubleVector2D QGeoProjectionWebMercator::viewportToWrappedMapProjection(const QDoubleVector2D &itemPosition) const
 {
     double s;
@@ -350,6 +357,8 @@ void QGeoProjectionWebMercator::setupCamera()
     int intZoomLevel = static_cast<int>(std::floor(m_cameraData.zoomLevel()));
     m_sideLength = (1 << intZoomLevel) * defaultTileSize;
     m_center = m_centerMercator * m_sideLength;
+    //aperture(90 / 2) = 1
+    m_aperture = tan(QLocationUtils::radians(m_cameraData.fieldOfView()) * 0.5);
 
     double f = m_viewportHeight;
     double z = std::pow(2.0, m_cameraData.zoomLevel() - intZoomLevel) * defaultTileSize;
@@ -358,15 +367,13 @@ void QGeoProjectionWebMercator::setupCamera()
     double z_mercator = std::pow(2.0, m_cameraData.zoomLevel()) * defaultTileSize;
     double altitude_mercator = f / (2.0 * z_mercator);
 
-    //aperture(90 / 2) = 1
-    m_aperture = tan(QLocationUtils::radians(m_cameraData.fieldOfView()) * 0.5);
     // calculate eye
     m_eye = m_center;
     m_eye.setZ(altitude * defaultTileSize / m_aperture);
 
     // And in mercator space
     m_eyeMercator = m_centerMercator;
-    m_eyeMercator.setZ(altitude_mercator);
+    m_eyeMercator.setZ(altitude_mercator  / m_aperture);
 
     m_view = m_eye - m_center;
     QDoubleVector3D side = QDoubleVector3D::normal(m_view, QDoubleVector3D(0.0, 1.0, 0.0));
@@ -402,7 +409,7 @@ void QGeoProjectionWebMercator::setupCamera()
         m_eyeMercator = mTiltMercator * m_viewMercator + m_centerMercator;
     }
 
-    m_view = m_eye - m_center;
+    m_view = m_eye - m_center; // ToDo: this should be inverted (center - eye), and the rest should follow
     m_viewNormalized = m_view.normalized();
     m_up = QDoubleVector3D::normal(m_view, m_side);
 
@@ -455,7 +462,7 @@ void QGeoProjectionWebMercator::setupCamera()
     m_transformation.scale(m_sideLength, m_sideLength, 1.0);
 
     m_centerNearPlane = m_eye + m_viewNormalized;
-    m_centerNearPlaneMercator = m_eyeMercator + m_viewNormalized * m_nearPlaneMercator;
+    m_centerNearPlaneMercator = m_eyeMercator - m_viewNormalized * m_nearPlaneMercator;
 
     // The method does not support tilting angles >= 90.0 or < 0.
 
@@ -505,6 +512,46 @@ void QGeoProjectionWebMercator::updateVisibleRegion()
     m_visibleRegion.clear();
     if (res.size())
         m_visibleRegion = QClipperUtils::pathToQList(res[0]); // Intersection between two convex quadrilaterals should always be a single polygon
+
+    m_projectableRegion.clear();
+    if (m_cameraData.tilt() == 0) {
+        m_projectableRegion = mapRect;
+    } else {
+        QGeoProjectionWebMercator::Plane nearPlane(m_centerNearPlaneMercator, m_viewNormalized);
+        Line2D nearPlaneXYIntersection = nearPlane.planeXYIntersection();
+        double squareHalfSide = qMax(5.0, nearPlaneXYIntersection.m_point.length());
+        QDoubleVector2D viewDirectionProjected = -m_viewNormalized.toVector2D().normalized();
+
+
+        QDoubleVector2D tl = nearPlaneXYIntersection.m_point
+                            - squareHalfSide * nearPlaneXYIntersection.m_direction
+                            + 2 * squareHalfSide * viewDirectionProjected;
+        QDoubleVector2D tr = nearPlaneXYIntersection.m_point
+                            + squareHalfSide * nearPlaneXYIntersection.m_direction
+                            + 2 * squareHalfSide * viewDirectionProjected;
+        QDoubleVector2D bl = nearPlaneXYIntersection.m_point
+                            - squareHalfSide * nearPlaneXYIntersection.m_direction;
+        QDoubleVector2D br = nearPlaneXYIntersection.m_point
+                            + squareHalfSide * nearPlaneXYIntersection.m_direction;
+
+        QList<QDoubleVector2D> projectableRect;
+        projectableRect.push_back(bl);
+        projectableRect.push_back(br);
+        projectableRect.push_back(tr);
+        projectableRect.push_back(tl);
+
+
+        c2t::clip2tri clipperProjectable;
+        clipperProjectable.clearClipper();
+        clipperProjectable.addSubjectPath(QClipperUtils::qListToPath(mapRect), true);
+        clipperProjectable.addClipPolygon(QClipperUtils::qListToPath(projectableRect));
+
+        Paths resProjectable = clipperProjectable.execute(c2t::clip2tri::Intersection);
+        if (resProjectable.size())
+            m_projectableRegion = QClipperUtils::pathToQList(resProjectable[0]); // Intersection between two convex quadrilaterals should always be a single polygon
+        else
+            m_projectableRegion = viewportRect;
+    }
 }
 
 /*