Panda3D: 使用四个点创建立方体

from panda3d.core import *
from direct.showbase.ShowBase import ShowBase

class MyApp(ShowBase):
    def __init__(self):
        ShowBase.__init__(self)

        # 已知平面的4个点
        point1 = Point3(-1, 0, 0)
        point2 = Point3(0, 0, -1)
        point3 = Point3(1, 0, 0)
        point4 = Point3(0, 0, 1)

        # 计算平面的朝向
        v1 = point2 - point1
        v2 = point3 - point1
        normal = v1.cross(v2)
        normal.normalize()

        # 沿着朝向的方向向前向后各拉伸出一个单位形成一个立方体
        forward = normal
        up = Vec3(0, 1, 0)
        right = forward.cross(up)
        up = right.cross(forward)
        center = (point1 + point2 + point3 + point4) / 4
        size = 1.0
        forward *= size
        up *= size
        right *= size
        back = -forward
        down = -up
        left = -right

        # 计算出这个立方体8个顶点坐标
        corners = [
            center + forward + up + right,
            center + forward + up + left,
            center + forward + down + right,
            center + forward + down + left,
            center + back + up + right,
            center + back + up + left,
            center + back + down + right,
            center + back + down + left,
        ]

        # 根据8个坐标画出立方体
        vertex_data = GeomVertexData('cube', GeomVertexFormat.getV3(), Geom.UHStatic)
        vertex_writer = GeomVertexWriter(vertex_data, 'vertex')
        for corner in corners:
            vertex_writer.add_data3(corner)
        tris = GeomTriangles(Geom.UHStatic)
        tris.add_vertices(0, 2, 1)
        tris.add_vertices(1, 2, 3)
        tris.add_vertices(4, 5, 6)
        tris.add_vertices(5, 7, 6)
        tris.add_vertices(0, 1, 4)
        tris.add_vertices(1, 5, 4)
        tris.add_vertices(2, 6, 3)
        tris.add_vertices(3, 6, 7)
        tris.add_vertices(0, 4, 2)
        tris.add_vertices(2, 4, 6)
        tris.add_vertices(1, 3, 5)
        tris.add_vertices(3, 7, 5)
        geom = Geom(vertex_data)
        geom.add_primitive(tris)
        node = GeomNode('cube')
        node.add_geom(geom)
        cube = NodePath(node)
        cube.reparent_to(self.render)

app = MyApp()
app.run()