func (l loopRegion) ContainsCell(c s2.Cell) bool {
// Quick check if the cell is in the bounding box
if !l.RectBound().ContainsCell(c) {
return false
}
// Quick check to see if the first vertex is in the loop.
if !l.ContainsPoint(c.Vertex(0)) {
return false
}
// At this stage one vertex is in the loop, now we check that the edges of the cell do not cross
// the loop.
return !l.edgesCross(c)
}
func (l loopRegion) IntersectsCell(c s2.Cell) bool {
// Quick check if the cell intersects the bounding box
if !l.RectBound().IntersectsCell(c) {
return false
}
// Quick check to see if the first vertex is in the loop.
if l.ContainsPoint(c.Vertex(0)) {
return true
}
// At this stage the one vertex is outside the loop. We check if any of the edges of the cell
// cross the loop.
if l.edgesCross(c) {
return true
}
// At this stage we know that there is one point of the cell outside the loop and the boundaries
// do not interesect. The only way for the cell to intersect with the loop is if it contains the
// the loop. We test this by checking if an arbitrary vertex of the loop is inside the cell.
if c.RectBound().Contains(l.RectBound()) {
return c.ContainsPoint(l.Vertex(0))
}
return false
}
// returns true if the edges of the cell cross the edges of the loop
func (l loopRegion) edgesCross(c s2.Cell) bool {
return l.edgesCrossPoints([]s2.Point{c.Vertex(0), c.Vertex(1), c.Vertex(2), c.Vertex(3)})
}