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polygon.go
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/
polygon.go
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package clip
import (
"github.com/tidwall/geojson"
"github.com/tidwall/geojson/geometry"
)
func clipPolygon(
polygon *geojson.Polygon, clipper geojson.Object,
opts *geometry.IndexOptions,
) geojson.Object {
rect := clipper.Rect()
var newPoints [][]geometry.Point
base := polygon.Base()
rings := []geometry.Ring{base.Exterior}
rings = append(rings, base.Holes...)
for _, ring := range rings {
ringPoints := make([]geometry.Point, ring.NumPoints())
for i := 0; i < len(ringPoints); i++ {
ringPoints[i] = ring.PointAt(i)
}
if clippedRing := clipRing(ringPoints, rect); len(clippedRing) > 0 {
newPoints = append(newPoints, clippedRing)
}
}
var exterior []geometry.Point
var holes [][]geometry.Point
if len(newPoints) > 0 {
exterior = newPoints[0]
}
if len(newPoints) > 1 {
holes = newPoints[1:]
}
newPoly := geojson.NewPolygon(
geometry.NewPoly(exterior, holes, opts),
)
if newPoly.Empty() {
return geojson.NewMultiPolygon(nil)
}
return newPoly
}