Pygame cannot make image bigger over time

Question

I am trying to make an image get bigger over time for a cool effect.

I've tried using this:

import pygame
from pygame.locals import *

pygame.init()


class Image(pygame.sprite.Sprite):
    default_imgresizer = pygame.transform.scale

    def __init__(self, win, x, y):
        pygame.sprite.Sprite.__init__(self)

        self.win = win

        self.x = x
        self.y = y

        self.maxsize = [500, 500]  # (not used yet)
        self.size = [0, 0]

        self.image = pygame.image.load("museum_pic.jpg")
        self.image = self.default_imgresizer(self.image, self.size)

        self.rect = self.image.get_rect(center=(self.x, self.y))

    def increase_size(self):
        self.size[0] += 5
        self.size[1] += 5

        self.image = self.default_imgresizer(self.image, self.size)
        self.rect = self.image.get_rect(center=(self.x, self.y))

        self.win.blit(self.image, self.size)

This is the event loop:

screen = pygame.display.set_mode((850, 600))

image = Image(screen, 100, 100)

running = True

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

    image.increase_size()

    pygame.display.update()

But then, nothing showed up on the screen.

How do I make an image get bigger over time?

Answer 1

First the image is scaled down to a size of (0, 0). After that you are upscaling the reduced image. Hence the picture is all black. Even if you reduce the image to a size larger than 0 and then upscale the image, it will result in a large loss of quality.
Do not scale the scaled image, but scale the original image:

self.original_image = pygame.image.load("museum_pic.jpg")

self.image = self.default_imgresizer(self.original_image, self.size)

Keep the aspect ratio of the image when you calculate the scale:

self.size[1] += 5
self.size[0] = self.size[1] * self.original_image.get_width() // self.original_image.get_height()

---

Minimal example:

import pygame
from pygame.locals import *

pygame.init()

class Image(pygame.sprite.Sprite):
    default_imgresizer = pygame.transform.scale

    def __init__(self, win, x, y):
        pygame.sprite.Sprite.__init__(self)
        self.win = win
        self.x = x
        self.y = y
        self.maxsize = [500, 500]  # (not used yet)
        self.size = [0, 0]
        #self.original_image = pygame.image.load("museum_pic.jpg")
        self.original_image = pygame.image.load(r"C:\source\PyGameExamplesAndAnswers\resource\icon\AirPlaneFront1-256.png")
        self.image = self.default_imgresizer(self.original_image, self.size)
        self.rect = self.image.get_rect(center=(self.x, self.y))

    def increase_size(self):
        self.size[1] += 5
        self.size[0] = self.size[1] * self.original_image.get_width() // self.original_image.get_height()
        self.image = self.default_imgresizer(self.original_image, self.size)
        self.rect = self.image.get_rect(center=(self.x, self.y))
        self.win.blit(self.image, self.rect)

screen = pygame.display.set_mode((500, 500))
image = Image(screen, *screen.get_rect().center)
clock = pygame.time.Clock()
running = True
while running:
    clock.tick(100)
    for event in pygame.event.get():
        if event.type == QUIT:
            running = False
        if event.type == pygame.KEYDOWN:
            image.size = [0, 0]

    screen.fill(0)
    image.increase_size()
    pygame.display.update()

pygame.quit()
exit()