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I'm trying to make a color picker that changes color over time. I have the logic but the process is really slow, the idea is to have a square that changes color and overlap a PNG grayscale gradient onto it so that the program can be faster. The problem is that I can't seem to download the gradient with the transparency.

import sys, pygame
pygame.init()

#VARIABLES
width = 255
height = 255

background = (255, 0, 0)
foreground = (230, 100, 45)

mySurf = pygame.Surface((255, 255))
mySurf.set_alpha(0)
mySurf.fill((200,0,200))

#SCREEN
screen = pygame.display.set_mode((width, height))
screen.fill((0, 0, 0))

#CODE
for x in range(255):
    s = pygame.Surface((1, 255))
    s.set_alpha(255-x)
    s.fill((255, 255, 255))
    mySurf.blit(s, (x, 0))

for y in range(255):
    s = pygame.Surface((255, 1))
    s.set_alpha(y)
    s.fill((0, 0, 0))
    mySurf.blit(s, (0, y))

pygame.image.save(mySurf, "gradient.png")

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    pygame.display.update()
Rabbid76
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Francesco
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1 Answers1

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You have to create a surface with a format that hast an alpha channel per pixel. Use the SRCALPHA flag:

mysurf = pygame.surface((255, 255))

mySurf = pygame.Surface((255, 255), pygame.SRCALPHA)

Note, with the flag each pixel has its own alpha value (RGBA format), without the flag the surfaces hast just 1 global alpha value and can not store different alpha values for the pixels (RGB format)

Complete example:

import sys, pygame
pygame.init()

#VARIABLES
width = 255
height = 255

background = (255, 0, 0)
foreground = (230, 100, 45)

mySurf = pygame.Surface((255, 255))
mySurf.set_alpha(0)
mySurf.fill((200,0,200))

#SCREEN
screen = pygame.display.set_mode((width, height), pygame.SRCALPHA)

#CODE
s = pygame.Surface((1, 255), pygame.SRCALPHA)
for x in range(255):
    s.fill((255, 255, 255, 255-x))
    mySurf.blit(s, (x, 0))

s = pygame.Surface((255, 1), pygame.SRCALPHA)
for y in range(255):
    s.fill((0, 0, 0, y))
    mySurf.blit(s, (0, y))

pygame.image.save(mySurf, "gradient.png")

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    pygame.display.update()
Rabbid76
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  • i just tried but it still saves the image without the transparency – Francesco Aug 10 '22 at 11:27
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    @Francesco use SRCALPHA for all surfacrs. Do not use set_alpha, but use a color with 4 compnents (RGBA). I can't write a complete answer now, because I' m on a journey an have just my smartphone – Rabbid76 Aug 10 '22 at 11:46
  • THANK YOU, using it on all surfeces worked perfectly, thank you so much, i just wish i knew why but this is perfect thank you – Francesco Aug 10 '22 at 12:11
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    @Francesco With the flag each pixel has its own alpha value (RGBA format), without the flag the surfacrs hast just 1 global alpha value and can not store different alpha values for the pixels (RGB format) – Rabbid76 Aug 10 '22 at 12:21