64 lines
2.1 KiB
Go
64 lines
2.1 KiB
Go
// Copyright 2017 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package s2
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// ContainsVertexQuery is used to track the edges entering and leaving the
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// given vertex of a Polygon in order to be able to determine if the point is
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// contained by the Polygon.
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//
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// Point containment is defined according to the semi-open boundary model
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// which means that if several polygons tile the region around a vertex,
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// then exactly one of those polygons contains that vertex.
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type ContainsVertexQuery struct {
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target Point
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edgeMap map[Point]int
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}
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// NewContainsVertexQuery returns a new query for the given vertex whose
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// containment will be determined.
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func NewContainsVertexQuery(target Point) *ContainsVertexQuery {
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return &ContainsVertexQuery{
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target: target,
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edgeMap: make(map[Point]int),
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}
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}
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// AddEdge adds the edge between target and v with the given direction.
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// (+1 = outgoing, -1 = incoming, 0 = degenerate).
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func (q *ContainsVertexQuery) AddEdge(v Point, direction int) {
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q.edgeMap[v] += direction
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}
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// ContainsVertex reports a +1 if the target vertex is contained, -1 if it is
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// not contained, and 0 if the incident edges consisted of matched sibling pairs.
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func (q *ContainsVertexQuery) ContainsVertex() int {
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// Find the unmatched edge that is immediately clockwise from Ortho(P).
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referenceDir := Point{q.target.Ortho()}
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bestPoint := referenceDir
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bestDir := 0
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for k, v := range q.edgeMap {
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if v == 0 {
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continue // This is a "matched" edge.
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}
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if OrderedCCW(referenceDir, bestPoint, k, q.target) {
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bestPoint = k
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bestDir = v
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}
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}
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return bestDir
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}
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