To implement vertex snapping, we're going to add some new methods to MapToolMixin. We'll start with the findFeatureAt() method. This method finds a feature close to the click location. Here is the implementation of this method:
def findFeatureAt(self, pos, excludeFeature=None):
mapPt,layerPt = self.transformCoordinates(pos)
tolerance = self.calcTolerance(pos)
searchRect = QgsRectangle(layerPt.x() - tolerance,
layerPt.y() - tolerance,
layerPt.x() + tolerance,
layerPt.y() + tolerance)
request = QgsFeatureRequest()
request.setFilterRect(searchRect)
request.setFlags(QgsFeatureRequest.ExactIntersect)
for feature in self.layer.getFeatures(request):
if excludeFeature != None:
if feature.id() == excludeFeature.id():
continue
return feature
return None