How to scale an image by window size?

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I have a square, non-resizable, pygame window and the size of it is calculated by monitor size. I have images that aren't square that I want created scaled by window size. I want it to be scaled by my SCREEN_SIZE variable. Here is my code, it puts an image up in the middle of the screen, but if you change your resolution the image stays the same size:

import pygame

pygame.init()

# Sets screen size by using your monitors resolution
SCREEN_SIZE = pygame.display.Info().current_h/1.65 

screen = pygame.display.set_mode((int(SCREEN_SIZE), int(SCREEN_SIZE)))

gameRunning = True

""" This is the part I need help with. When I run my program the image is the correct 
size, but when I change my resolution the image stays the same size and the window's 
size changes. I need the image to proportionally scale with the window. """
imgSize = 0.2
img = pygame.image.load(r"location of an image on your PC")
img = pygame.transform.smoothscale(img, (int(img.get_width() * imgSize), int(img.get_height() * imgSize))) 

rect = img.get_rect()
rect.center = (screen.get_width()/2, screen.get_height()/2)

while gameRunning == True:
    pygame.display.update()

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            gameRunning = False
            pygame.quit()
            break

    screen.fill((255,255,255))



    screen.blit(img, rect)

For the code to work you will need to sub in an image location for the "img" variable and mess with the imgSize variable.

math pygame graphics python
1 Answers

Compare the ration of the width and the ratio of the height. Scale the image by the minimum ratio. This works even with non-square window resolutions.

ratio_x = screen.get_width() / img.get_width()
ratio_y = screen.get_height() / img.get_height()
scale = min(ratio_x, ratio_y)
img = pygame.transform.smoothscale(img, (int(img.get_width() * scale), int(img.get_height() * scale)))

Minimal example:

import pygame

pygame.init()

screen = pygame.display.set_mode((300, 300))

img = pygame.image.load(r"parrot1.png")
scale = min(screen.get_width() / img.get_width(), screen.get_height() / img.get_height())
img = pygame.transform.smoothscale(img, 
          (round(img.get_width() * scale), round(img.get_height() * scale))) 

rect = img.get_rect(center = screen.get_rect().center)

gameRunning = True
while gameRunning == True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            gameRunning = False

    screen.fill((127,127,127))
    screen.blit(img, rect)
    pygame.display.flip()

pygame.quit()
exit()
user_55777650
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