Why is the circle moving in a straight line instead of at an angle in pygame? - python-3.x

Question

I am learning the basics of pygame in my free time at work. I wanted to move the bottom boundary of my program up, but when I changed the boundary collision condition, the ball moves in a straight line instead of at an angle.
When I delete the 525 part of the condition in the bounceCircle definition, it moves as expected. When I place it back, it moves in a horizontal line.
import pygame
import sys
import random
import math
# Initalize the game engine
pygame.init()
# Define common colors:
WHITE = (255, 255, 255)
BLUE = (0, 0, 255)
# Set window size, title, and background color
(width, height) = (900, 600)
screen = pygame.display.set_mode((width, height))
pygame.display.set_caption("Ball Playground")
screen.fill(WHITE)
# Used to manage how fast the screen updates
clock = pygame.time.Clock()
# Ball class
class Particles():
def __init__(self, position, radius):
self.x = position[0]
self.y = position[1]
self.radius = radius
self.color = (BLUE)
# thickness = 0 means filled
# thickness > 0 thicker border
# thickness < 0 nothing
self.thickness = 1
self.speed = 0
self.angle = 0
# Definition for drawing circle
def drawCircle(self):
pygame.draw.circle(screen, self.color, (int(self.x), int(self.y)), self.radius, self.thickness)
# Definition for moving the circle
def moveCircle(self):
self.x += math.sin(self.angle) * self.speed
self.y -= math.cos(self.angle) * self.speed
# Definition for bouncing off of surfaces
def bounceCircle(self):
if (self.x > width - self.radius) or (self.x < self.radius):
self.angle = - self.angle
elif (self.y > height - self.radius) or (self.y < 525 - self.radius):
self.angle = math.pi - self.angle
ball = Particles((450, 300), 40)
ball.speed = 2
ball.angle = random.uniform(0, math.pi*2)
# --------- Main Program Loop ----------
while True:
# --- Main Event Loop
for event in pygame.event.get():
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
pygame.display.update()
screen.fill(WHITE)
#--- Game Logic
ball.moveCircle()
ball.bounceCircle()
ball.drawCircle()
#--- Drawings
pygame.draw.line(screen, BLACK, [0, 525], [900, 525], 2)
# Prints tiny diaginal lines to mark surface
x1 = 0
x2 = 5
for i in range(0, width):
pygame.draw.line(screen, BLACK, [x1, 530], [x2, 525], 2)
x1 += 5
x2 += 5
pygame.display.flip()
clock.tick(60)

Answer 1

You need to edit the bounceCircle function to:
def bounceCircle(self):
if (self.x + self.radius > width ) or (self.x - self.radius < 0):
self.angle = - self.angle
elif (self.y + self.radius > (525)) or (self.y - self.radius < 0):
self.angle = math.pi - self.angle
Whole Code (fixed a few bugs):
import pygame
import sys
import random
import math
# Initalize the game engine
pygame.init()
# Define common colors:
WHITE = (255, 255, 255)
BLUE = (0, 0, 255)
# Set window size, title, and background color
(width, height) = (900, 600)
screen = pygame.display.set_mode((width, height))
pygame.display.set_caption("Ball Playground")
screen.fill(WHITE)
# Used to manage how fast the screen updates
clock = pygame.time.Clock()
# Ball class
class Particles():
def __init__(self, position, radius):
self.x = position[0]
self.y = position[1]
self.radius = radius
self.color = (BLUE)
# thickness = 0 means filled
# thickness > 0 thicker border
# thickness < 0 nothing
self.thickness = 1
self.speed = 0
self.angle = 0
# Definition for drawing circle
def drawCircle(self):
pygame.draw.circle(screen, self.color, (int(self.x), int(self.y)), self.radius, self.thickness)
# Definition for moving the circle
def moveCircle(self):
self.x += math.sin(self.angle) * self.speed
self.y -= math.cos(self.angle) * self.speed
print(self.angle, self.x, self.y)
# Definition for bouncing off of surfaces
def bounceCircle(self):
if (self.x > width - self.radius) or (self.x < self.radius):
self.angle = - self.angle
elif (self.y + self.radius > (height-100)) or (self.y - self.radius < 0):
self.angle = math.pi - self.angle
ball = Particles((450, 300), 40)
ball.speed = 20
ball.angle = random.uniform(0, math.pi*2)
print(ball.angle)
# --------- Main Program Loop ----------
while True:
# --- Main Event Loop
for event in pygame.event.get():
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
pygame.display.update()
screen.fill(WHITE)
#--- Game Logic
ball.moveCircle()
ball.bounceCircle()
ball.drawCircle()
#--- Drawings
pygame.draw.line(screen, BLUE, [0, 525], [900, 525], 2)
# Prints tiny diaginal lines to mark surface
x1 = 0
x2 = 5
for i in range(0, width):
pygame.draw.line(screen, BLUE, [x1, 530], [x2, 525], 2)
x1 += 5
x2 += 5
pygame.display.flip()
clock.tick(60)