问题
I'm trying to write this tutorial in Pygame(Python) and having problems about holding points between planes.
My code is: fiz2.py
Vector class: vector.py
If you move mouse on the Pygame screen, the planes will rotate. And when the planes are rotating, points are passing through planes and going outside.
I tried to fix points' positions on every iteration but they still passed the planes. I have no idea about where should I fix their positions.
NOTE: I know my code is a little bit messy, this is my first 2d program and I had really hard times getting used to Pygame's coordinate plane and vectors. I will re-write when I solve this.
NOTE2: Yes, I wrote the comment about how to hold points between planes on the tutorial, I understand the way he fixes positions but have no idea about how(and where, in code) to implement it.
Thanks.
回答1:
I can't tell looking at the code. My guess is a variable-timestep, causing instability. But I can't verify if the math is right. Although, I have useful information :
Vectors
You can simplify code, by using vectors as a class vs list/tuple. (velocity, acceleration, location) are treated as one object, verses separate .x and .y values.
# example:
pos[0] += vel[0]
pos[1] += vel[1]
# vs
pos += vel
There is a python-only implementation: euclid.py You can use to compare with your vector.py.
Or use NumPy [ used for 3d graphics, in openGL. ] Is a popular, mature lib.
physics
(It looks like you want to learn by writing your own physics), but check out PyMunk
colors
You can use: pygame.Color
import pygame
from pygame import Color
color = Color('white')
color2 = Color('lightgray')
color3 = Color(0,128,128)
collisions #
Look at pygame.sprite.*collide , and pygame.Rect.*collide
pygame Game loop with numpy vector's
Boilerplate I wrote
""" Pygame boilerplate. <ninmonkey>2011/04
pygame main Game() loop, and numpy for vector math.
note:
this might not be the most effecient way to use numpy as vectors, but it's an intro.
And this does not force fixed-timesteps. If you want a stable simulation, you need to use a fixed timestep.
see: http://gafferongames.com/game-physics/fix-your-timestep/
Keys:
ESC : exit
Space : game_init()
"""
import pygame
from pygame.locals import *
from pygame import Color, Rect
import numpy as np
def get_screen_size():
"""return screen (width, height) tuple"""
screen = pygame.display.get_surface()
return screen.get_size()
class Actor():
"""basic actor, moves randomly.
members:
loc = position vector
velocity = velocity vector
width, height
"""
def __init__(self, loc=None, velocity=None):
"""optional initial loc and velocity vectors"""
self.width = 50
self.height = 50
# if loc or velocity are not set: use random
if loc is None: self.rand_loc()
else: self.loc = loc
if velocity is None: self.rand_velocity()
else: self.velocity = velocity
def update(self):
"""update movement"""
self.loc += self.velocity
def rand_velocity(self):
"""set a random vector , based on random direction. Using unit circle:
x = cos(deg) * speed
"""
rad = np.radians( np.random.randint(0,360) )
speed = np.random.randint(1,15)
x = np.cos(rad)
y = np.sin(rad)
velocity = np.array( [x,y])
velocity *= speed
self.velocity = velocity
def rand_loc(self):
"""random location onscreen"""
width,height = get_screen_size()
x = np.random.randint(0,width)
y = np.random.randint(0,height)
self.loc = np.array([x,y])
def is_onscreen(self):
"""test is screen.colliderect(actor) true?"""
x,y = self.loc
w,h = get_screen_size()
screen = Rect(0, 0, w, h)
actor = Rect(x, y, self.width, self.height)
if screen.colliderect(actor): return True
else: return False
class GameMain():
"""game Main entry point. handles intialization of game and graphics."""
done = False
debug = False
color_gray = Color('lightgray')
def __init__(self, width=800, height=600, color_bg=None):
"""Initialize PyGame"""
pygame.init()
self.width, self.height = width, height
self.screen = pygame.display.set_mode(( self.width, self.height ))
pygame.display.set_caption( "boilerplate : pygame" )
self.clock = pygame.time.Clock()
self.limit_fps = True
self.limit_fps_max = 60
if color_bg is None: color_bg = Color(50,50,50)
self.color_bg = color_bg
self.game_init()
def game_init(self):
"""new game/round"""
self.actors = [Actor() for x in range(10)]
def loop(self):
"""Game() main loop"""
while not self.done:
self.handle_events()
self.update()
self.draw()
if self.limit_fps: self.clock.tick( self.limit_fps_max )
else: self.clock.tick()
def update(self):
"""update actors, handle physics"""
for a in self.actors:
a.update()
if not a.is_onscreen():
a.rand_loc()
def handle_events(self):
"""handle regular events. """
events = pygame.event.get()
# kmods = pygame.key.get_mods() # key modifiers
for event in events:
if event.type == pygame.QUIT: sys.exit()
elif event.type == KEYDOWN:
if (event.key == K_ESCAPE): self.done = True
elif (event.key == K_SPACE): self.game_init()
def draw(self):
"""render screen"""
# clear screen
self.screen.fill( self.color_bg )
# Actor: draw
for a in self.actors:
x,y = a.loc
w,h = a.width, a.height
r = Rect(x, y, w, h)
self.screen.fill(self.color_gray, r)
# will call update on whole screen Or flip buffer.
pygame.display.flip()
if __name__ == '__main__':
g = GameMain()
g.loop()
来源：https://stackoverflow.com/questions/5677890/pygame-simple-physics-engine-how-to-hold-points-between-planes