The code creates 3D coordinates for the cube and then displays them on the 2D screen but you can still see the back faces of the cube. I just want to tell the code not to draw the points that are behind the faces in the 3D coordinates.
points = [(-1,-1,-1),(-1,-1,1),(-1,1,1),(-1,1,-1),
(1,-1,-1),(1,-1,1),(1,1,1),(1,1,-1), ]#coords for points
faces = [(3,0,4,7),(1,5,6,2),(2,1,0,3),(5,4,7,6),(3,2,6,7),(0,1,5,4)]
These are the coordinates of the points and which points should be joined to which
def flattenPoint(point):
(x, y, z) = (point[0], point[1], point[2])
xnew = x#x axis rotation
ynew = y * math.cos(rotatedanglex) - z * math.sin(rotatedanglex)
znew = y * math.sin(rotatedanglex) + z * math.cos(rotatedanglex)
xnew = znew * math.sin(rotatedangley) + xnew * math.cos(rotatedangley)
ynew = ynew #y axis rotation
znew = ynew * math.cos(rotatedangley) - xnew * math.sin(rotatedangley)
projectedY = int(height / 2 + ((ynew * distance) / (znew + distance)) * scale)
projectedX = int(width / 2 + ((xnew * distance) / (znew + distance)) * scale)
return (projectedX, projectedY, znew)
def createOutline(points):
a, b, c, d = points[0], points[1], points[2], points[3]
coords = ((b[0], b[1]), (a[0], a[1]), (d[0], d[1]),(c[0], c[1]))
pygame.draw.polygon(screen, blue, coords, 1)
''' The FlattenPoint function rotates the 3D points and then turns them into 2D coordinates that are displayed. '''
def createFace(points):
a, b, c, d = points[0], points[1], points[2], points[3]
coords = ((b[0], b[1]), (a[0], a[1]), (d[0], d[1]),(c[0], c[1]))
pygame.draw.polygon(screen, green, coords)
createFace joins up the 2D coordinates.
def render(points, faces):
coords = []
for point in points:
coords.append(flattenPoint(point))
screen.fill(screencolour)
for face in faces:
createFace((coords[face[0]], coords[face[1]], coords[face[2]], coords[face[3]]))
for face in faces:#must draw outline after all the faces have been drawn
createOutline((coords[face[0]], coords[face[1]], coords[face[2]],coords[face[3]]))
'''
Compute the normal vector to of a face and cull the faces where the normal vector points away from the view. The normal vector can be computed with the Cross product :
def cross(a, b):
return [a[1]*b[2] - a[2]*b[1], a[2]*b[0] - a[0]*b[2], a[0]*b[1] - a[1]*b[0]]
Use the cross product and cull the faces:
def createFace(points):
a, b, c, d = points[0], points[1], points[2], points[3]
v1 = b[0]-a[0], b[1]-a[1], b[2]-a[2]
v2 = c[0]-a[0], c[1]-a[1], c[2]-a[2]
n = cross(v1, v2)
if n[2] < 0:
return
coords = ((b[0], b[1]), (a[0], a[1]), (d[0], d[1]),(c[0], c[1]))
pygame.draw.polygon(screen, green, coords)
You have to ensure that the winding order of all the faces in counter clockwise. See also Face Culling and Back-face culling
Change the vertices and indices as follows:
points = [(-1,-1,-1),( 1,-1,-1), (1, 1,-1),(-1, 1,-1),
(-1,-1, 1),( 1,-1, 1), (1, 1, 1),(-1, 1, 1)]
faces = [(0,1,2,3),(5,4,7,6),(4,0,3,7),(1,5,6,2),(4,5,1,0),(3,2,6,7)]
However, I recommend to implement a depth test. See Pygame rotating cubes around axis and Does PyGame do 3d? .
Complete example:
import pygame
import math
points = [(-1,-1,-1),( 1,-1,-1), (1, 1,-1),(-1, 1,-1),
(-1,-1, 1),( 1,-1, 1), (1, 1, 1),(-1, 1, 1)]
faces = [(0,1,2,3),(5,4,7,6),(4,0,3,7),(1,5,6,2),(4,5,1,0),(3,2,6,7)]
def flattenPoint(point):
(x, y, z) = (point[0], point[1], point[2])
xnew = x#x axis rotation
ynew = y * math.cos(rotatedanglex) - z * math.sin(rotatedanglex)
znew = y * math.sin(rotatedanglex) + z * math.cos(rotatedanglex)
xnew = znew * math.sin(rotatedangley) + xnew * math.cos(rotatedangley)
ynew = ynew #y axis rotation
znew = ynew * math.cos(rotatedangley) - xnew * math.sin(rotatedangley)
projectedY = int(height / 2 + ((ynew * distance) / (znew + distance)) * scale)
projectedX = int(width / 2 + ((xnew * distance) / (znew + distance)) * scale)
return (projectedX, projectedY, znew)
def cross(a, b):
return [a[1]*b[2] - a[2]*b[1], a[2]*b[0] - a[0]*b[2], a[0]*b[1] - a[1]*b[0]]
def createOutline(points):
a, b, c, d = points[0], points[1], points[2], points[3]
v1 = b[0]-a[0], b[1]-a[1], b[2]-a[2]
v2 = c[0]-a[0], c[1]-a[1], c[2]-a[2]
n = cross(v1, v2)
if n[2] < 0:
return
coords = ((b[0], b[1]), (a[0], a[1]), (d[0], d[1]),(c[0], c[1]))
pygame.draw.polygon(screen, blue, coords, 3)
def createFace(points):
a, b, c, d = points[0], points[1], points[2], points[3]
v1 = b[0]-a[0], b[1]-a[1], b[2]-a[2]
v2 = c[0]-a[0], c[1]-a[1], c[2]-a[2]
n = cross(v1, v2)
if n[2] < 0:
return
coords = ((b[0], b[1]), (a[0], a[1]), (d[0], d[1]),(c[0], c[1]))
pygame.draw.polygon(screen, green, coords)
def render(points, faces):
coords = []
for point in points:
coords.append(flattenPoint(point))
screen.fill(screencolour)
for face in faces:
createFace((coords[face[0]], coords[face[1]], coords[face[2]], coords[face[3]]))
for face in faces:#must draw outline after all the faces have been drawn
createOutline((coords[face[0]], coords[face[1]], coords[face[2]],coords[face[3]]))
pygame.init()
screen = pygame.display.set_mode((500, 500))
clock = pygame.time.Clock()
rotatedanglex = 0.0
rotatedangley = 0.0
width, height = screen.get_size()
distance = 200.0
scale = 75.0
green = (0, 255, 0)
blue = (0, 0, 255)
screencolour = (0, 0, 0)
run = True
while run:
clock.tick(60)
for event in pygame.event.get():
if event.type == pygame.QUIT:
run = False
screen.fill(0)
render(points, faces)
pygame.display.flip()
rotatedanglex += 0.01
rotatedangley += 0.02
pygame.quit()
exit()
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