Python: 2次元図で凸多角形の内部のイベントを得る

この記事の Awkward のバージョンは1.X.Xです

例外処理はちゃんとしてないので注意せよ。

import numpy as np
import awkward as ak
import matplotlib.pyplot as plt

# 配列作成
obj={}
rs = np.random.RandomState(0)
obj["memx"]=rs.rand(1000)
obj["memy"]=rs.rand(1000)
memx = "memx"
memy = "memy"
tree = ak.Array(obj)

# グラフ化
plt.scatter(tree[memx],tree[memy])
plt.plot(pointx,pointy,color="tab:red")
plt.xlim(-0.1,1.1)
plt.ylim(-0.1,1.1)
plt.show()

def get_in_convex_polygon(tree, memx, memy, pointx, pointy):
    assert(len(pointx)==len(pointy))
    assert(pointx[0]==pointx[-1])
    assert(pointy[0]==pointy[-1])
    assert(len(pointx)>=4)
    
    dx = pointx[1]-pointx[0]
    dy = pointy[1]-pointy[0]
    if ((pointx[2]-pointx[0])*dy-(pointy[2]-pointy[0])*dx)>0:
        # 回転方向を合わせる
        pointx.reverse()
        pointy.reverse()
    
    for i in range(len(pointx)-1):
        dx = pointx[i+1]-pointx[i+0]
        dy = pointy[i+1]-pointy[i+0]
        tree = tree[((tree[memx]-pointx[i])*dy-(tree[memy]-pointy[i])*dx)<0]
    return tree

# 三角形の点列 (終点は始点と同じにせよ)
pointx = [0.0,0.6,0.3,0.0]
pointy = [0.0,0.0,0.5,0.0]

tree = get_in_convex_polygon(tree,memx,memy,pointx,pointy)

# グラフ化
plt.scatter(tree[memx],tree[memy])
plt.plot(pointx,pointy,color="tab:red")
plt.xlim(-0.1,1.1)
plt.ylim(-0.1,1.1)
plt.show()

凸多角形って言うけど、凸って字は凸多角形ではないんだよなあ。