Show actually visible canvas area in overview (possibly rotated)

Fix #11862

src/gui/qgsmapoverviewcanvas.cpp

@@ -33,6 +33,8 @@
 //! widget that serves as rectangle showing current extent in overview
 class QgsPanningWidget : public QWidget
 {
+    QPolygon mPoly;
+
   public:
     QgsPanningWidget( QWidget* parent )
         : QWidget( parent )
@@ -42,26 +44,24 @@ class QgsPanningWidget : public QWidget
       setAttribute( Qt::WA_NoSystemBackground );
     }
 
-    void resizeEvent( QResizeEvent* r ) override
+    void setPolygon( const QPolygon& p )
     {
-      QSize s = r->size();
-      QRegion reg( 0, 0, s.width(), s.height() );
-      QRegion reg2( 2, 2, s.width() - 4, s.height() - 4 );
-      QRegion reg3 = reg.subtracted( reg2 );
-      setMask( reg3 );
+      if ( p == mPoly ) return;
+      mPoly = p;
+      setGeometry( p.boundingRect() );
+      repaint();
     }
 
 
     void paintEvent( QPaintEvent* pe ) override
     {
       Q_UNUSED( pe );
 
-      QRect r( QPoint( 0, 0 ), size() );
       QPainter p;
       p.begin( this );
       p.setPen( Qt::red );
-      p.setBrush( Qt::red );
-      p.drawRect( r );
+      QPolygonF t = mPoly.translated( -mPoly.boundingRect().left(), -mPoly.boundingRect().top() );
+      p.drawConvexPolygon( t );
       p.end();
     }
 
@@ -122,70 +122,14 @@ void QgsMapOverviewCanvas::drawExtentRect()
     return;
   }
 
+  const QPolygonF& vPoly = mMapCanvas->mapSettings().visiblePolygon();
   const QgsMapToPixel& cXf = mSettings.mapToPixel();
-  QgsPoint ll( extent.xMinimum(), extent.yMinimum() );
-  QgsPoint ur( extent.xMaximum(), extent.yMaximum() );
-
-  // transform the points before drawing
-  cXf.transform( &ll );
-  cXf.transform( &ur );
-
-#if 0
-  // test whether panning widget should be drawn
-  bool show = false;
-  if ( ur.x() >= 0 && ur.x() < width() )
-    show = true;
-  if ( ll.x() >= 0 && ll.x() < width() )
-    show = true;
-  if ( ur.y() >= 0 && ur.y() < height() )
-    show = true;
-  if ( ll.y() >= 0 && ll.y() < height() )
-    show = true;
-  if ( !show )
-  {
-    QgsDebugMsg( "panning: extent out of overview area" );
-    mPanningWidget->hide();
-    return;
-  }
-#endif
-
-  // round values
-  int x1 = static_cast<int>( ur.x() + 0.5 ), x2 = static_cast<int>( ll.x() + 0.5 );
-  int y1 = static_cast<int>( ur.y() + 0.5 ), y2 = static_cast<int>( ll.y() + 0.5 );
-
-  if ( x1 > x2 )
-    std::swap( x1, x2 );
-  if ( y1 > y2 )
-    std::swap( y1, y2 );
-
-#ifdef Q_OS_MAC
-  // setGeometry (Qt 4.2) is causing Mac window corruption (decorations
-  // are drawn at odd locations) if both coords are at limit. This may
-  // have something to do with Qt calculating dimensions as x2 - x1 + 1.
-  // (INT_MAX - INT_MIN + 1 is UINT_MAX + 1)
-  if ( x1 == INT_MIN && x2 == INT_MAX )
-    x1 += 1;  // x2 -= 1 works too
-  if ( y1 == INT_MIN && y2 == INT_MAX )
-    y1 += 1;
-#endif
-
-  QRect r( x1, y1, x2 - x1 + 1, y2 - y1 + 1 );
-
-  // allow for 5 pixel minimum widget size
-  if ( r.width() < 5 && x1 > INT_MIN + 2 ) // make sure no underflow occurs (2 is largest adjustment)
-  {
-    r.setX( r.x() - (( 5 - r.width() ) / 2 ) );  // adjust x  by 1/2 the difference of calculated and min. width
-    r.setWidth( 5 );
-  }
-  if ( r.height() < 5 && y1 > INT_MIN + 2 )
-  {
-    r.setY( r.y() - (( 5 - r.height() ) / 2 ) );  // adjust y
-    r.setHeight( 5 );
-  }
-
-  QgsDebugMsg( QString( "panning: extent to widget: [%1,%2] [%3x%4]" ).arg( x1 ).arg( y1 ).arg( r.width() ).arg( r.height() ) );
-
-  mPanningWidget->setGeometry( r );
+  QVector< QPoint > pts;
+  pts.push_back( cXf.transform( QgsPoint(vPoly[0]) ).toQPointF().toPoint() );
+  pts.push_back( cXf.transform( QgsPoint(vPoly[1]) ).toQPointF().toPoint() );
+  pts.push_back( cXf.transform( QgsPoint(vPoly[2]) ).toQPointF().toPoint() );
+  pts.push_back( cXf.transform( QgsPoint(vPoly[3]) ).toQPointF().toPoint() );
+  mPanningWidget->setPolygon( QPolygon(pts) );
   mPanningWidget->show(); // show if hidden
 }