3D图形的深度问题

Question

我最近在YouTube上复制了一段代码，其中涉及不使用OpenGL之类3D模块的Python 3D图形。该视频仅适用于多维数据集，因此我尝试在形状中添加四面体，然后事情突然出现在原本不应该出现的地方。代码如下：

import pygame, sys, math, random

def rotate2d(pos, rad): x,y=pos; s,c = math.sin(rad),math.cos(rad); return x*c-y*s,y*c+x*s

class Cam:
    def __init__(self, pos=(0,0,0),rot=(0,0)):
        self.pos = list(pos)
        self.rot = list(rot)

    def events(self, event):
        if event.type == pygame.MOUSEMOTION:
            x, y = event.rel; x/=200; y/=200
            self.rot[0]+=y; self.rot[1]+=x

    def update(self, dt, key):
        s = dt*10

        if key[pygame.K_q]: self.pos[1]+=s
        if key[pygame.K_e]: self.pos[1]-=s

        x,y = s*math.sin(self.rot[1]),s*math.cos(self.rot[1])
        if key[pygame.K_w]: self.pos[0]+=x; self.pos[2]+=y
        if key[pygame.K_s]: self.pos[0]-=x; self.pos[2]-=y
        if key[pygame.K_a]: self.pos[0]-=y; self.pos[2]+=x
        if key[pygame.K_d]: self.pos[0]+=y; self.pos[2]-=x
        if key[pygame.K_r]: self.pos[0]=0; self.pos[1]=0;\
                                         self.pos[2]=-5; self.rot[0]=0; self.rot[1]=0


class Cube:
    faces = (0,1,2,3),(4,5,6,7),(0,1,5,4),(2,3,7,6),(0,3,7,4),(1,2,6,5)
    colors = (255,0,0),(255,128,0),(255,255,0),(255,255,255),(0,0,255),(0,255,0)
    def __init__(self,pos=(0,0,0),v0=(-1,-1,-1),v1=(1,-1,-1),v2=(1,1,-1),v3=(-1,1,-1),v4=(-1,-1,1),v5=(1,-1,1),v6=(1,1,1),v7=(-1,1,1)):
        self.vertices = (v0,v1,v2,v3,v4,v5,v6,v7)
        x,y,z = pos
        self.verts = [(x+X/2,y+Y/2,z+Z/2) for X,Y,Z in self.vertices]

class Tetrahedron:
    faces = (1,2,3),(0,1,2),(0,1,3),(0,2,3)
    colors = (255,0,0),(255,128,0),(255,255,0),(255,255,255)
    def __init__(self,pos=(0,0,0),v0=(0,0,.866),v1=(-.866,-1,-1),v2=(-.866,1,-1),v3=(.866,0,-1)):
        self.vertices = (v0,v1,v2,v3)
        x,y,z = pos
        self.verts = [(x+X/2,y+Y/2,z+Z/2) for X,Y,Z in self.vertices]

pygame.init()
w,h = 400,400; cx,cy = w//2, h//2
screen = pygame.display.set_mode((w,h))
clock = pygame.time.Clock()
cam = Cam((0,0,-5))
pygame.event.get(); pygame.mouse.get_rel()
pygame.mouse.set_visible(0); pygame.event.set_grab(1)

objects = [Cube((0,0,0)),Cube((0,0,2)),Tetrahedron((0,0,1))]

while True:
    dt = clock.tick()/1000

    for event in pygame.event.get():
        if event.type == pygame.QUIT: pygame.quit(); sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE: pygame.quit(); sys.exit()
        cam.events(event)

    screen.fill((0,0,0))

    face_list = []; face_color = []; depth = []

    for obj in objects:

        vert_list = []; screen_coords = []
        for x,y,z in obj.verts:
            x-=cam.pos[0]; y-=cam.pos[1];z-=cam.pos[2]
            x,z=rotate2d((x,z),cam.rot[1])
            y,z = rotate2d((y,z),cam.rot[0])
            vert_list += [(x,y,z)]

            f = 200/z
            x,y = x*f,y*f
            screen_coords+=[(cx+int(x),cy+int(y))]

        for f in range(len(obj.faces)):
            face = obj.faces[f]

            on_screen = False
            for i in face:
                x,y = screen_coords[i]
                if vert_list[i][2]>0 and x>0 and x<w and y>0 and y<h: on_screen = True; break

            if on_screen:
                coords = [screen_coords[i] for i in face]
                face_list += [coords]
                face_color += [obj.colors[f]]
                depth += [sum(sum(vert_list[j][i] for j in face)**2 for i in range(3))]

    order = sorted(range(len(face_list)),key=lambda i:depth[i],reverse=1)

    for i in order:
        try: pygame.draw.polygon(screen,face_color[i],face_list[i])
        except: pass

    key = pygame.key.get_pressed()
    pygame.display.flip()
    cam.update(dt,key)

[我的问题是，当cam.pos距离对象至少7.5时，四面体部分通过两侧的立方体显示出来：如您所见，四面体本应被埋在立方体下，但仍在增加。有人可以建议对代码进行编辑，以阻止四面体通过任何对象显示吗？

Answer 1

您可以尝试使用面部的平均z值进行深度排序：

example