Re: [pygame] How to draw a simple circle and make it move with keyboard input?

On Nov 30, 2018, at 11:44 AM, Marc-Alexandre Espiaut <marc-alexandre.espiaut@xxxxxxxxx> wrote:
Hello,
Thank you for your answer.

I’m hoping the this was not a homework assignment (I am a teacher).

No, I am a PhD student. It was for my own sake.

But, because you showed your code, I’ll help you out.

Thank you, as I’ve been a student in the past, and might be a teacher also in a near future, I know asking for help always works better when you have something to show.

Most of your code was fine, but some things were in the wrong place.

Thank you for your code. I’m quite surprised many of the thing I’ve done were redundant.
The code works fine, but now I’m wondering how to keep the circle moving while the key is pressed. I’ve tried to change some if into while but that only gets the program stuck.
The idea should be something like while event.type == pygame.KEYDOWN then update the position before drawing the screen. But I don’t see how, yet.
Thank you again, and best regards.
Marc-Alexandre Espiaut
On 11/30/18 5:28 PM, Irv Kalb wrote:
Hi,

I'm hoping the this was not a homework assignment (I am a teacher). But, because you showed your code, I'll help you out.

Most of your code was fine, but some things were in the wrong place.

The basic idea is that there should be a main loop, and in that loop, you check for events (key down, etc.), adjust anything you need to adjust, then draw everything.

Hope this helps:
#!/usr/bin/env python

import pygame

import sys # needed to quit gracefully

#import pygame.draw

N_PIXELS_TO_MOVE = 5 # how many pixels to move on each keypress

FRAMES_PER_SECOND = 30 # How fast to draw - this says draw every 30th of a second

def main():

pygame.init()

clock = pygame.time.Clock() # added to allow things to slow down

screen = pygame.display.set_mode((640, 480))

pygame.display.set_caption('pygame test')

# You don't need this. screen.fill below does this for you.

#s = pygame.Surface(screen.get_size(), pygame.SRCALPHA, 32)

# Pick a starting X, Y location for the circle

circleX = 0

circleY = 0

while True:

# You don't need this

#screen.blit(s, (0, 0))

for event in pygame.event.get():

if event.type == pygame.QUIT:

pygame.quit() # quit pygame

sys.exit() # quit the program

if event.type == pygame.KEYDOWN:

if event.key == pygame.K_ESCAPE or event.unicode == 'q':

pygame.quit()

sys.exit()

# If user presses left, right, up, or down, change the appropriate coordinate

elif event.key == pygame.K_LEFT:

circleX = circleX - N_PIXELS_TO_MOVE

elif event.key == pygame.K_RIGHT:

circleX = circleX + N_PIXELS_TO_MOVE

elif event.key == pygame.K_UP:

circleY = circleY - N_PIXELS_TO_MOVE

elif event.key == pygame.K_DOWN:

circleY = circleY + N_PIXELS_TO_MOVE

# Now do all the drawing, first the background (fill)

screen.fill((0, 0, 0))

# Then draw the circle at the circle's coordinates

pygame.draw.circle(screen, (255, 255, 255, 255), (circleX, circleY), 50)

pygame.display.flip() # or: pygame.display.update()

clock.tick(FRAMES_PER_SECOND) # make PyGame wait the correct amount

if __name__ == '__main__':

main()

Irv
On Nov 30, 2018, at 7:29 AM, Marc-Alexandre Espiaut <marc-alexandre.espiaut@xxxxxxxxx> wrote:
Hello,
I’ve tried to make a simple pygame code.
I would like to draw a circle, and make it move with keyboard input.
I would like to achieve that with the most minimalist code possible, but so far I don’t manage to do such a thing.
Here is my non working code for reference:
#!/usr/bin/env python

import pygame
import pygame.draw

def main():
    pygame.init()

    screen = pygame.display.set_mode((640, 480))
    pygame.display.set_caption('pygame test')
    screen.fill((0, 0, 0))

    s = pygame.Surface(screen.get_size(), pygame.SRCALPHA, 32)

    pygame.draw.circle(s, (255, 255, 255, 255), (0, 0), 50)

    screen.blit(s, (0, 0))
    pygame.display.flip()

    try:
        while True:
            event = pygame.event.wait()
            if event.type == pygame.QUIT:
                break
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_ESCAPE or event.unicode == 'q':
                    break
            pygame.display.flip()
    finally:
        pygame.quit()

if __name__ == '__main__':
    main()
I’ve looked at the pygame examples, but I really struggle to get a clear idea about this. So far aliens.py and chimp.py uses a pygame.Rect in some way… but as I’ve said, the code is not clear. I don’t understand how the binding of the Rect happens with the moving objects, and how updating is handled.
If anybody can enlighten me on that matter, I would be happy to read it.
Best regards,
Marc-Alexandre Espiaut