double QgsTolerance::computeMapUnitPerPixel( QgsMapLayer* layer, const QgsMapSettings& mapSettings )
{
if ( ! mapSettings.hasCrsTransformEnabled() )
{
// if the on-the-fly projections are not enabled, layer units pre pixel are the same as map units per pixel
return mapSettings.mapUnitsPerPixel();
}
// the layer is projected. Find out how many pixels are in one map unit - either horizontal and vertical direction
// this check might not work correctly in some cases
// (on a large area the pixels projected around "0,0" can have different properties from the actual point)
QgsPoint p1 = toLayerCoordinates( layer, mapSettings, QPoint( 0, 1 ) );
QgsPoint p2 = toLayerCoordinates( layer, mapSettings, QPoint( 0, 2 ) );
QgsPoint p3 = toLayerCoordinates( layer, mapSettings, QPoint( 1, 0 ) );
QgsPoint p4 = toLayerCoordinates( layer, mapSettings, QPoint( 2, 0 ) );
double x = p1.sqrDist( p2 );
double y = p3.sqrDist( p4 );
if ( x > y )
{
return sqrt( x );
}
else
{
return sqrt( y );
}
}
// return ratio [mu/lu] between map units and layer units
// this is of course only an approximation
double _ratioMU2LU( const QgsMapSettings& mapSettings, QgsMapLayer* layer )
{
double distMU = mapSettings.mapUnitsPerPixel();
QgsPoint ptMapCenterMU = mapSettings.visibleExtent().center();
QgsPoint ptMapCenterRightMU( ptMapCenterMU.x() + distMU, ptMapCenterMU.y() );
QgsPoint ptMapCenterLU = mapSettings.mapToLayerCoordinates( layer, ptMapCenterMU );
QgsPoint ptMapCenterRightLU = mapSettings.mapToLayerCoordinates( layer, ptMapCenterRightMU );
double distLU = sqrt( ptMapCenterLU.sqrDist( ptMapCenterRightLU ) );
double ratio = distMU / distLU;
return ratio;
}
double QgsTolerance::toleranceInProjectUnits( double tolerance, QgsMapLayer* layer, const QgsMapSettings& mapSettings, QgsTolerance::UnitType units )
{
// converts to map units
if ( units == ProjectUnits )
return tolerance;
else if ( units == Pixels )
return tolerance * mapSettings.mapUnitsPerPixel();
else // units == LayerUnits
{
// [mu] = [lu] * [mu/lu]
return tolerance * _ratioMU2LU( mapSettings, layer );
}
}
int QgsDecorationGrid::yGridLines( const QgsMapSettings &mapSettings, QList< QPair< qreal, QLineF > > &lines ) const
{
// prepare vertical lines
lines.clear();
if ( mGridIntervalX <= 0.0 )
{
return 1;
}
const QgsMapToPixel &m2p = mapSettings.mapToPixel();
// draw nothing if the distance between grid lines would be less than 1px
// otherwise the grid lines would completely cover the whole map
//if ( mapBoundingRect.height() / mGridIntervalY >= p->device()->height() )
if ( mGridIntervalX / mapSettings.mapUnitsPerPixel() < 1 )
return 1;
const QPolygonF &canvasPoly = canvasPolygon( mapSettings );
const QPolygonF &mapPolygon = canvasExtent( mapSettings );
QLineF lineSouth( mapPolygon[3], mapPolygon[2] );
QLineF lineNorth( mapPolygon[0], mapPolygon[1] );
double len = lineSouth.length();
Q_ASSERT( std::fabs( len - lineNorth.length() ) < 1e-6 ); // no shear
const QRectF &mapBoundingRect = mapPolygon.boundingRect();
double roundCorrection = mapBoundingRect.left() > 0 ? 1.0 : 0.0;
double dist = static_cast< int >( ( mapBoundingRect.left() - mGridOffsetX ) / mGridIntervalX + roundCorrection ) * mGridIntervalX + mGridOffsetX;
dist = dist - mapBoundingRect.left();
while ( dist < len )
{
double t = dist / len;
QPointF p0( lineNorth.pointAt( t ) );
QPointF p1( lineSouth.pointAt( t ) );
QLineF line( p0, p1 );
clipByRect( line, canvasPoly );
line = QLineF( m2p.transform( QgsPointXY( line.pointAt( 0 ) ) ).toQPointF(), m2p.transform( QgsPointXY( line.pointAt( 1 ) ) ).toQPointF() );
lines.push_back( qMakePair( p0.x(), line ) );
dist += mGridIntervalX;
}
return 0;
}
