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>

2 files changed, 38 insertions, 17 deletions

diff --git a/src/location/declarativemaps/qdeclarativepolygonmapitem.cpp b/src/location/declarativemaps/qdeclarativepolygonmapitem.cpp
index daa1a9fc..3218f9f1 100644
--- a/src/location/declarativemaps/qdeclarativepolygonmapitem.cpp
+++ b/src/location/declarativemaps/qdeclarativepolygonmapitem.cpp
@@ -53,6 +53,8 @@
 
 /* poly2tri triangulator includes */
 #include <clip2tri.h>
+#include <earcut.hpp>
+#include <array>
 
 QT_BEGIN_NAMESPACE
 
@@ -185,7 +187,7 @@ void QGeoMapPolygonGeometry::updateSourcePoints(const QGeoMap &map,
 
     // 2)
     QList<QList<QDoubleVector2D> > clippedPaths;
-    const QList<QDoubleVector2D> &visibleRegion = map.geoProjection().visibleRegion();
+    const QList<QDoubleVector2D> &visibleRegion = map.geoProjection().projectableRegion();
     if (visibleRegion.size()) {
         c2t::clip2tri clipper;
         clipper.addSubjectPath(QClipperUtils::qListToPath(wrappedPath), true);
@@ -306,23 +308,42 @@ void QGeoMapPolygonGeometry::updateScreenPoints(const QGeoMap &map)
 
     screenOutline_ = ppi;
 
-    QTriangleSet ts = qTriangulate(ppi);
-    qreal *vx = ts.vertices.data();
-
-    screenIndices_.reserve(ts.indices.size());
-    screenVertices_.reserve(ts.vertices.size());
+    using Coord = double;
+    using N = uint32_t;
+    using Point = std::array<Coord, 2>;
+
+    std::vector<std::vector<Point>> polygon;
+    polygon.push_back(std::vector<Point>());
+    std::vector<Point> &poly = polygon.front();
+    // ... fill polygon structure with actual data
+
+    for (int i = 0; i < ppi.elementCount(); ++i) {
+        const QPainterPath::Element e = ppi.elementAt(i);
+        if (e.isMoveTo() || i == ppi.elementCount() - 1
+                || (qAbs(e.x - poly.front()[0]) < 0.1
+                    && qAbs(e.y - poly.front()[1]) < 0.1)) {
+            Point p = { e.x, e.y };
+            poly.push_back( p );
+        } else if (e.isLineTo()) {
+            Point p = { e.x, e.y };
+            poly.push_back( p );
+        } else {
+            qWarning("Unhandled element type in polygon painterpath");
+        }
+    }
 
-    if (ts.indices.type() == QVertexIndexVector::UnsignedInt) {
-        const quint32 *ix = reinterpret_cast<const quint32 *>(ts.indices.data());
-        for (int i = 0; i < (ts.indices.size()/3*3); ++i)
-            screenIndices_ << ix[i];
-    } else {
-        const quint16 *ix = reinterpret_cast<const quint16 *>(ts.indices.data());
-        for (int i = 0; i < (ts.indices.size()/3*3); ++i)
-            screenIndices_ << ix[i];
+    if (poly.size() > 2) {
+        // Run tessellation
+        // Returns array of indices that refer to the vertices of the input polygon.
+        // Three subsequent indices form a triangle.
+        screenVertices_.clear();
+        screenIndices_.clear();
+        for (const auto &p : poly)
+            screenVertices_ << QPointF(p[0], p[1]);
+        std::vector<N> indices = mapbox::earcut<N>(polygon);
+        for (const auto &i: indices)
+            screenIndices_ << quint32(i);
     }
-    for (int i = 0; i < (ts.vertices.size()/2*2); i += 2)
-        screenVertices_ << QPointF(vx[i], vx[i + 1]);
 
     screenBounds_ = ppi.boundingRect();
 }
diff --git a/src/location/declarativemaps/qdeclarativepolylinemapitem.cpp b/src/location/declarativemaps/qdeclarativepolylinemapitem.cpp
index aedb9811..26f030b0 100644
--- a/src/location/declarativemaps/qdeclarativepolylinemapitem.cpp
+++ b/src/location/declarativemaps/qdeclarativepolylinemapitem.cpp
@@ -226,7 +226,7 @@ QList<QList<QDoubleVector2D> > QGeoMapPolylineGeometry::clipPath(const QGeoMap &
 
     // 2)
     QList<QList<QDoubleVector2D> > clippedPaths;
-    const QList<QDoubleVector2D> &visibleRegion = map.geoProjection().visibleRegion();
+    const QList<QDoubleVector2D> &visibleRegion = map.geoProjection().projectableRegion();
     if (visibleRegion.size()) {
         c2t::clip2tri clipper;
         clipper.addSubjectPath(QClipperUtils::qListToPath(wrappedPath), false);