How to make a circular object jump using pygame?

Question

I have just started using pygame, and I'm stuck.

I'm not getting any syntax errors, but I'm sure there is some problem with the below code.

import pygame
import sys

pygame.init()
pygame.display.set_caption('Jumper Game')

display_width = 500
display_height = 500
the_game_is_on = True

ball_pos_x = 200
ball_pos_y = 500
ball_radius = 20
ball_color = [0,0,255]
speed = 1

is_jump = False
m = 1
v = 5

dis = pygame.display.set_mode((display_width,display_height)) #screen

while the_game_is_on:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT] and ball_pos_x > 20:
        ball_pos_x-= speed
    if keys[pygame.K_RIGHT] and ball_pos_x < (display_width - (ball_radius)):
        ball_pos_x+= speed
    if not (is_jump):
        if keys[pygame.K_UP] and ball_pos_y > 20:
            ball_pos_y-= speed
        if keys[pygame.K_DOWN] and ball_pos_y < (display_height - (ball_radius)):
            ball_pos_y+= speed
        if keys[pygame.K_SPACE]:
            is_jump = True
    else:
        f = (1/2)*m*(v**2)
        ball_pos_y-=f
        v-=1
        if v < 0:
            m = -1
        if v >= ((v+1)*-1): #to check the initial position
            is_jump = False
    pygame.time.delay(10)
    dis.fill((0,0,0))
    pygame.draw.circle(dis,ball_color,(ball_pos_x,int(ball_pos_y)),ball_radius)
    pygame.display.update()
pygame.display.quit()

For writing the code for jump, I referred to this website, the source code in this website works perfectly.

"some problem" means nothing particular really and I would not expect too many users here interested in analyzing your code just to figure out what you wanted to ask about. — Marcin Orlowski, Jul 09 '20 at 19:34
Ya, so the blue ball works perfectly when going sideways, up and down. But it suddenly disappears when I press the space bar. @JoranBeasley — Adarsh Raj, Jul 09 '20 at 19:35
Try printing out the y position for the ball after you hit space. I suspect the ball is launching into crazy high or low positions not viewable in the camera very quickly. — code11, Jul 09 '20 at 19:40

score 2 · Accepted Answer · answered Jul 09 '20 at 19:48

You have to compute m dependnet on v < 0:

m = -1 if v < 0 else 1

The jump has to end if v < -5 and when the jump ends, then v has to be reset (v = 5):

jump_h = 5 # try 10 for higher jumps
v = jump_h

while the_game_is_on:
    # [...]

    if not is_jump:
        # [...]

    else:
        if v >= -jump_h:
            m = -1 if v < 0 else 1
            f = (1/2)*m*(v**2)
            v -=1
            ball_pos_y -= f
        else:
            is_jump = False
            v = jump_h

score 0 · Answer 2 · answered Jul 09 '20 at 20:09

I think you are hitting Python2 vs. Python3 difference:

$ python3
Python 3.7.7 (default, Mar 13 2020, 21:39:43) 
[GCC 9.2.1 20190827 (Red Hat 9.2.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> m = 1
>>> v = 5
>>> (1/2)*m*(v**2)
12.5

In Python2, 1 / 2 equals 0, but when you use float: 1.0 / 2 is 0.5:

$ python2
Python 2.7.18 (default, Apr 21 2020, 18:49:31) 
[GCC 9.3.1 20200408 (Red Hat 9.3.1-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> m = 1
>>> v = 5
>>> (1/2)*m*(v**2)
0
>>> (float(1)/2)*m*(v**2)
12.5

How to make a circular object jump using pygame?

2 Answers2

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