PyGame没有正确绘制圆圈

Question

def collide(p1, p2):
    dx = p1.x - p2.x
    dy = p1.y - p2.y
    dist = math.hypot(dx, dy)

    if dist < p1.size + p2.size:
        for i in range (0,1):
            neutrList.append(Neutron(xxx,yyy))
        for k,neutroon in enumerate(neutrList):
            neutroon.verletUpdate(dt)
            neutroon.bounce()
            neutroon.display()       

screen = pygame.display.set_mode((width, height))
screen.fill(background_colour)
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    screen.fill(background_colour)

    for k, at in enumerate(partList):
        neutron.verletUpdate(dt)
        neutron.bounce()
        collide(at, neutron)
        if not len(neutrList):
            neutron.display()
        at.display()

    pygame.display.flip()
pygame.quit()

This is a part of my program. I wanted to draw green circle moving away from blue circle.Blue circle is static and is fine. But instead of green circle I get something like this What should I change to make my code working properly?

Neutron class

class Neutron():
    def __init__(self, x, y):
        self.x = x
        self.y = y
        self.vx = 2.5
        self.vy = 0
        self.A = 235
        self.Z = 92
        self.size = 20
        self.colour = (0, 255, 0)
        self.thickness = 0

    def verletUpdate(self,dt):
        self.x = self.x + dt * self.vx
        self.y = self.y + dt * self.vy

    def display(self):
       pygame.draw.circle(screen, self.colour, (int(self.x), int(self.y)), self.size, self.thickness)

    def bounce(self):
        if self.x > width - self.size:
            self.x = 2*(width - self.size) - self.x
            self.vx = -self.vx

        elif self.x < self.size:
            self.x = 2*self.size - self.x
            self.vx = -self.vx

        if self.y > height - self.size:
            self.y = 2*(height - self.size) - self.y
            self.vy= -self.vy

        elif self.y < self.size:
            self.y = 2*self.size - self.y
            self.vy = -self.vy

Answer 1

I think that the reason you are seeing the smear is because you are drawing a whole bunch of neutrons. You are creating a new one when running the collide() function. See this line:

neutrList.append(Neutron(xxx,yyy))

You are appending a new neutron to your list, and when you go to draw them, you are drawing all of them, each with a slightly different position. You should check this by printing len(neutrlist) every frame and see if it is constantly growing.

Also, why is your collide() fuction drawing and creating neutrons? Should it just adjust their position/velocity based on collisions? It is not a good design choice to have a collision check function draw and create the objects that are colliding. Neutron drawing and creating should happen elsewhere in your program.