How to render transparent text with alpha channel in PyGame?

Question

I am using pygame.font.Font.render() to render some text. I'd like the text to be translucent, ie have an alpha value other than 255, so I tried passing a color argument with an alpha value (eg (255, 0, 0, 150)) as the color argument for pygame.font.Font.render() but it didn't have any effect. I also tried using pygame.Surface.convert_alpha() on the resulting Surface object, but that didn't do anything either. Any ideas?

Answer 1

I'm not sure why, but after some experimentation I have discovered that the surface created with font.render cannot have it's alpha value changed. Just blit that surface to another surface, and change the alpha value of the new surface.

textsurface=font.render('Test', True, (0, 0, 0))
surface=pygame.Surface((100, 30))
surface.fill((255, 255, 255))
surface.blit(textsurface, pygame.Rect(0, 0, 10, 10))
surface.set_alpha(50)
window.blit(surface, pygame.Rect(0, 30, 10, 10))

Answer 2

When using the pygame.font module, the alpha channel of the text color is not taken into account when rendering a text, but see pygame.font.Font.render:

Antialiased images are rendered to 24-bit RGB images. If the background is transparent a pixel alpha will be included.

and pygame.Surface.set_alpha

Changed in pygame 2.0: per-surface alpha can be combined with per-pixel alpha.

Hence it is completely sufficient to set the transparency after rendering the text with set_alpha. This even works for anti-aliased text:

font = pygame.font.SysFont(None, 150)

text_surf = font.render('test text', True, (255, 0, 0))
text_surf.set_alpha(127)

window.blit(text_surf, (x, y))

Minimal example: repl.it/@Rabbid76/PyGame-TransparentText

import pygame

pygame.init()
window = pygame.display.set_mode((500, 300))
clock = pygame.time.Clock()
font = pygame.font.SysFont(None, 150)

text_surf = font.render('test text', True, (255, 0, 0))
text_surf.set_alpha(127)

background = pygame.Surface(window.get_size())
ts, w, h, c1, c2 = 50, *window.get_size(), (128, 128, 128), (64, 64, 64)
tiles = [((x*ts, y*ts, ts, ts), c1 if (x+y) % 2 == 0 else c2) for x in range((w+ts-1)//ts) for y in range((h+ts-1)//ts)]
for rect, color in tiles:
    pygame.draw.rect(background, color, rect)

run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    window.blit(background, (0, 0))
    window.blit(text_surf, text_surf.get_rect(center = window.get_rect().center))
    pygame.display.flip()

pygame.quit()
exit()

---

By using the pygame.freetype module, you can use a transparent color directly when creating a text surface:

ft_font = pygame.freetype.SysFont('Times New Roman', 150)

text_surf2, text_rect2 = ft_font.render('test text', (255, 0, 0, 128))
window.blit(text_surf2, (x, y))

Or if you are rendering the text directly onto a surface:

ft_font = pygame.freetype.SysFont('Times New Roman', 150)

ft_font.render_to(window, (x, y), 'test text', (255, 0, 0, 128))

Minimal example: repl.it/@Rabbid76/PyGame-TransparentFreeTypeText

import pygame
import pygame.freetype

pygame.init()

window = pygame.display.set_mode((500, 300))
clock = pygame.time.Clock()
ft_font = pygame.freetype.SysFont('Times New Roman', 150)

text_surf2, text_rect2 = ft_font.render('test text', (255, 0, 0, 128))

background = pygame.Surface(window.get_size())
ts, w, h, c1, c2 = 50, *window.get_size(), (128, 128, 128), (64, 64, 64)
tiles = [((x*ts, y*ts, ts, ts), c1 if (x+y) % 2 == 0 else c2) for x in range((w+ts-1)//ts) for y in range((h+ts-1)//ts)]
for rect, color in tiles:
    pygame.draw.rect(background, color, rect)

run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    window.blit(background, (0, 0))
    
    text_rect = ft_font.get_rect('test text')
    text_rect.center = (window.get_width() // 2, window.get_height() // 2 - 70)
    ft_font.render_to(window, text_rect.topleft, 'test text', (255, 0, 0, 128))
    
    text_rect2.center = (window.get_width() // 2, window.get_height() // 2 + 70)
    window.blit(text_surf2, text_rect2)
    
    pygame.display.flip()

pygame.quit()
exit()

See also Text and font