python-如何使球在pygame中从三角形弹回？

triangle = [(250,220),(400,300),(100,300)]

三角形可以由pygame.draw.polygon()绘制

pygame.draw.polygon(WINDOW,RED,triangle,0)

使用pygame.math.Vector2定义球的位置和运动矢量：

ballvec = pygame.math.Vector2(1,1)
ballpos = pygame.math.Vector2(150,250)
balldiameter = 64

创建一个函数,执行碰撞检测.该功能必须检测球是否命中线.如果击中线,则球的运动矢量将反映在线上.
该线由2个点(lp0,lp1)表示,它们是pygame.math.Vector2对象.
球的位置(pt)和运动矢量(dir)也是pygame.math.Vector2个对象：

def isect(lp0,lp1,pt,dir,radius):
    # direction vector of the line
    l_dir = (lp1 - lp0).normalize()
    # normal vector to the line
    nv = pygame.math.Vector2(-l_dir[1],l_dir[0])
    # distance to line
    d = (lp0-pt).dot(nv)
    # intersection point on endless line
    ptX = pt + nv * d
    # test if the ball hits the line
    if abs(d) > radius or dir.dot(ptX-pt) <= 0:
        return dir
    if (ptX-lp0).dot(l_dir) < 0 or (ptX-lp1).dot(l_dir) > 0:
        return dir 
    # reflect the direction vector on the line (like a billiard ball)
    r_dir = dir.reflect(nv)
    return r_dir

将窗口矩形和三角形追加到线列表中.蚀刻线由2 pygame.math.Vector2个对象的元组表示：

# add screen rect
screen_rect = [(0,0),(0,(500,0)]
for i in range(len(screen_rect)):
    p0,p1 = screen_rect[i],screen_rect[(i+1) % len(screen_rect)]
    line_list.append((pygame.math.Vector2(p0[0],p0[1]),pygame.math.Vector2(p1[0],p1[1])))

# add red trianlge
triangle = [(250,300)]
for i in range(len(triangle)):
    p0,p1 = triangle[i],triangle[(i+1) % len(triangle)]
    line_list.append((pygame.math.Vector2(p0[0],p1[1])))

遍历直线的循环中进行碰撞检测.如果球撞到线,则运动矢量将替换为反射的运动矢量：

for line in line_list:
    ballvec = isect(*line,ballpos,ballvec,balldiameter/2)

最后更新球的位置和球矩形：

ballpos = ballpos + ballvec
ballRect.x,ballRect.y = ballpos[0]-ballRect.width/2,ballpos[1]-ballRect.height/2

请参阅示例代码,在该示例中,我将建议的更改应用于原始代码.我的球图像的尺寸为64×64.球直径必须设置为此尺寸(球直径= 64)：

import pygame # importing the pygame
import sys # importing the system libraries
import time # importing timer
import random
from pygame.locals import * # importing the locals functions from the pygame library set
pygame.init() # the function from pygame that initializes all relevant variable

# setting length and width
width = 500
length = 300

# colour variables
WHITE = (255,255)
RED = (255,0)
GRAY = (128,128,128)

# importing ball image
ball = pygame.image.load("ball.png")
ballRect = ball.get_rect()

# setting ball data
ballvec = pygame.math.Vector2(1.5,1.5)
ballpos = pygame.math.Vector2(150,250)
balldiameter = 64

# setting window size
WINDOW = pygame.display.set_mode((width,length))# setting the size of the window

def isect(lp0,l_dir[0])
    # distance to line
    d = (lp0-pt).dot(nv)
    # intersection point on endless line
    ptX = pt + nv * d
    # test if the ball hits the line
    if abs(d) > radius or dir.dot(ptX-pt) <= 0:
        return dir
    if (ptX-lp0).dot(l_dir) < 0 or (ptX-lp1).dot(l_dir) > 0:
        return dir 
    # reflect the direction vector on the line (like a billiard ball)
    r_dir = dir.reflect(nv)
    return r_dir

line_list = []

# add screen rect
screen_rect = [(0,p1[1])))

# add blue triangle
triangle2 = [(250,80),0)]
for i in range(len(triangle2)):
    p0,p1 = triangle2[i],triangle2[(i+1) % len(triangle2)]
    line_list.append((pygame.math.Vector2(p0[0],p1[1])))

# loop
while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()

    WINDOW.fill(GRAY)
    pygame.draw.polygon(WINDOW,0)
    pygame.draw.polygon(WINDOW,BLUE,triangle2,0)
    WINDOW.blit(ball,ballRect)

    pygame.display.update()
    pygame.display.flip()
    time.sleep(0.002) # to slow down the speed of bouncing
    pygame.display.update()

    for line in line_list:
        ballvec = isect(*line,balldiameter/2)

    ballpos = ballpos + ballvec
    ballRect.x,ballpos[1]-ballRect.height/2

    pygame.display.update()