// Remove elements >= rightIter that make the curve concave after
// adding thisElem.
func (f *frontier) maybeRemoveRightElements(
thisElem frontierItem, rightIter rbtree.Iterator) {
if rightIter.Limit() {
return
}
ti := rightIter.Next()
for !ti.Limit() && !isConcave(thisElem, getItem(rightIter), getItem(ti)) {
tmp := rightIter
rightIter = ti
ti = ti.Next()
f.tree.DeleteWithIterator(tmp)
}
}
// Remove elements <= leftIter that make the curve concave after
// adding thisElem.
func (f *frontier) maybeRemoveLeftElements(
thisElem frontierItem, leftIter rbtree.Iterator) {
if leftIter.NegativeLimit() {
return
}
if getItem(leftIter).y >= thisElem.y {
tmp := leftIter
leftIter = leftIter.Prev()
f.tree.DeleteWithIterator(tmp)
}
if leftIter.NegativeLimit() {
return
}
ti := leftIter.Prev()
for !ti.NegativeLimit() && !isConcave(getItem(ti), getItem(leftIter), thisElem) {
tmp := leftIter
leftIter = ti
ti = ti.Prev()
f.tree.DeleteWithIterator(tmp)
}
}
func getItem(iter rbtree.Iterator) frontierItem {
return iter.Item().(frontierItem)
}