How do i stop an image from moving by the edges of the screen in Pygame? - pygame

Question

I just started with pygame and want to make a minigame with a weapon (pixelart). I made it move by arrow keys on the keyboard, but the image moves by the edges, how do I block it from going further than the edges? The dimensions of my "character" is 220x116 pixels
#!/usr/bin/env python
import pygame
from pygame.locals import *
from sys import exit
background_image = 'mario bg.png'
weapon = 'scar.png'
pygame.init()
SCREEN_SIZE = (800, 800)
screen = pygame.display.set_mode(SCREEN_SIZE, 0, 32)
pygame.display.set_caption("SCAR MINIGAME")
background = pygame.image.load(background_image).convert()
player = pygame.image.load(weapon).convert_alpha()
x, y = 150, 353
MOVE_RIGHT = x=+10
MOVE_LEFT = x=-10
MOVE_UP = y=-10
MOVE_DOWN = y=+10
direction = 0
while True:
for event in pygame.event.get():
if event.type == QUIT:
exit()
if event.type == KEYDOWN:
if event.key == K_LEFT:
MOVE_LEFT = False
elif event.key == K_RIGHT:
MOVE_RIGHT = False
elif event.key == K_DOWN:
MOVE_DOWN = False
elif event.key == K_UP:
MOVE_UP = False
elif event.type == KEYUP:
if event.key == K_LEFT:
MOVE_LEFT = True
elif event.key == K_RIGHT:
MOVE_RIGHT = True
elif event.key == K_UP:
MOVE_UP = True
elif event.key == K_DOWN:
MOVE_DOWN = True
if(direction == MOVE_LEFT):
x-=0.4
elif(direction == MOVE_RIGHT):
x+=0.4
elif(direction == MOVE_UP):
y-=0.4
elif(direction == MOVE_DOWN):
y+=0.4
screen.blit(background, (0, 0))
screen.blit(player, (x, y))
pygame.display.update()

Answer 1

You simply need to check the co-ordinates of the player, and restrict them to on-screen, or make them wrap around.
I find it's handy to keep the window dimensions in global variables, and use these in setup functions, and later calculations:
WINDOW_WIDTH=800
WINDOW_HEIGHT=800
screen = pygame.display.set_mode( (WINDOW_WIDTH,WINDOW_HEIGHT) , 0, 32)
So when you update the position of player:
# Check player is on-screen
if (player.x < 0):
player.x = 0
elif (player.x > WINDOW_WIDTH):
player.x = WINDOW_WIDTH
if (player.y < 0):
player.y = 0
elif (player.y > WINDOW_HEIGHT):
player.y = WINDOW_HEIGHT
screen.blit(background, (0, 0))
screen.blit(player, (x, y))
It would be a more complete answer to include the width of the sprite for the > WINDOW_WIDTH-sprite_width check so it still shows on-screen, but that exercise is left for the reader.
So back to the code. The new function keepPointOnScreen() takes a co-ordinate and checks that it's on the screen, modifying it if not. Calling this function each time the player position is updated keeps the sprite on-screen. Since the sprite is painted from the left-side, it's still possible to "hide" the sprite on the right & bottom. To fix this, the keeper function needs to take into account the bitmap width.
#!/usr/bin/env python
import pygame
from pygame.locals import *
from sys import exit
background_image = 'mario bg.png'
weapon = 'scar.png'
# Keep these as variables for checking later on the code
WINDOW_WIDTH=800
WINDOW_HEIGHT=800
# Setup the window
pygame.init()
SCREEN_SIZE = (WINDOW_WIDTH, WINDOW_HEIGHT)
screen = pygame.display.set_mode(SCREEN_SIZE, 0, 32)
pygame.display.set_caption("SCAR MINIGAME")
# load images & set starting positions
background = pygame.image.load(background_image).convert()
player = pygame.image.load(weapon).convert_alpha()
player_width = player.get_width()
player_height = player.get_height()
print("Player image is [%u x %u]" % (player_width, player_height))
x, y = 150, 353
direction = 0
clock = pygame.time.Clock()
###
### Given a co-ordinate, ensure the co-ordinate is inside the screen
### bounds. If it's outside the screen area, reduce it to inside,
### or wrap it to the other side
###
### The code uses the WINDOW_WIDTH and WINDOW_HEIGHT globals,
### Assuming the window is 0 to WIDTH-1 in pixels, and similiarly for height
####
def keepPointOnScreen(x,y, bm_width, bm_height, wrap=False):
global WINDOW_WIDTH, WINDOW_HEIGHT
if ( wrap == False ):
# Block on the edges of the screen (no wrapping)
if ( x < 0 ):
x = 0
elif ( x >= WINDOW_WIDTH-bm_width ):
x = WINDOW_WIDTH-bm_width-1
if ( y < 0 ):
y = 0
elif ( y >= WINDOW_HEIGHT-bm_height ):
y = WINDOW_HEIGHT-bm_height-1
else:
# Wrap-around from side to side and top to bottom
if ( x < 0 ):
x = WINDOW_WIDTH-bm_width-1
elif ( x >= WINDOW_WIDTH-bm_width ):
x = 0
if ( y < 0 ):
y = WINDOW_HEIGHT-bm_height-1
elif ( y >= WINDOW_HEIGHT-bm_width ):
y = 0
return x, y
while True:
for event in pygame.event.get():
if ( event.type == QUIT ):
exit()
# Movement keys
keys = pygame.key.get_pressed()
if ( keys[pygame.K_LEFT] ):
x -= 1
elif ( keys[pygame.K_RIGHT] ):
x += 1
elif ( keys[pygame.K_UP] ):
y -= 1
elif ( keys[pygame.K_DOWN] ):
y += 1
# make sure the point is still on-screen
x,y = keepPointOnScreen( x, y, player_width, player_height )
# re-paint the window
screen.blit(background, (0, 0))
screen.blit(player, (x, y))
pygame.display.update()
clock.tick(60) # no more than 60 FPS