Simple alpha blending as a special flag for `Surface.fill`

[Matiiss]

So basically add a flag that lets you do simple alpha blending using Surface.fill. It would be the equivalent of creating a surface with a certain alpha value and blitting that on the target surface, essentially this:

image = pygame.image.load(...).convert_alpha()

tint = pygame.Surface(image.get_size(), flags=pygame.SRCALPHA)
tint.fill((255, 0, 0, 100))  # red tint
image.blit(tint, (0, 0))

could turn into this:

image = pygame.image.load(...).convert_alpha()
image.fill((255, 0, 0, 100), special_flags=pygame.BLEND_RGBA)  # naming can be discussed obvs

[dr0id]

this can already be done?
img.fill((255, 255, 255, alpha), None, pygame.BLEND_RGBA_MULT)

[Matiiss]

this can already be done? img.fill((255, 255, 255, alpha), None, pygame.BLEND_RGBA_MULT)

That looks like the equivalent of set_alpha (I tested, it looks really similar anyway), also how does it handle the RGB part being something else? For example, (255, 0, 0, 100) which should give the image a red tint.

[dr0id]

yes, this is to set alpha and I must have missed this change (according to docs of set_alpha):
Changed in pygame 2.0: per-surface alpha can be combined with per-pixel alpha.

This was not possible and the fill method was a workaround for that.

Well you may be right:

# -*- coding: utf-8 -*-

from __future__ import print_function, division

import sys
import pygame


SCREENSIZE = 800, 600


def main():

    pygame.init()
    # screen = pygame.display.set_mode(SCREENSIZE, pygame.RESIZABLE | pygame.SRCALPHA, 32)
    screen = pygame.display.set_mode(SCREENSIZE)

    image = pygame.Surface((50, 50), pygame.SRCALPHA)
    pygame.draw.circle(image, (128, 128, 128), (25, 25), 25)
    pygame.draw.rect(image, (220, 220, 220), (5, 0, 10, 50))
    pygame.draw.rect(image, (80, 80, 80), (35, 0, 10, 50))

    flags = (
        (pygame.BLEND_RGBA_ADD,"BLEND_RGBA_ADD"),
        (pygame.BLEND_RGBA_MAX,"BLEND_RGBA_MAX"),
        (pygame.BLEND_RGBA_MIN,"BLEND_RGBA_MIN"),
        (pygame.BLEND_RGBA_MULT,"BLEND_RGBA_MULT"),
        (pygame.BLEND_RGBA_SUB,"BLEND_RGBA_SUB"),
        (pygame.BLENDMODE_ADD,"BLENDMODE_ADD"),
        (pygame.BLENDMODE_BLEND,"BLENDMODE_BLEND"),
        (pygame.BLENDMODE_MOD,"BLENDMODE_MOD"),
        (pygame.BLENDMODE_NONE,"BLENDMODE_NONE"),
    )

    image2 = image.copy()
    tint = pygame.Surface(image.get_size(), flags=pygame.SRCALPHA)
    tint.fill((255, 0, 0, 100))  # red tint
    image2.blit(tint, (0, 0))

    image3 = image.copy()
    tint = pygame.Surface(image.get_size(), flags=pygame.SRCALPHA)
    tint.fill((255, 0, 0, 100))  # red tint
    image3.blit(tint, (0, 0), None, pygame.BLEND_RGBA_MULT)

    font = pygame.font.Font(None, 18)

    running = True
    while running:
        # events
        for event in pygame.event.get():

            if event.type == pygame.QUIT:
                running = False
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_ESCAPE:
                    running = False

        # draw

        pygame.display.flip()
        screen.fill((0, 0, 0))
        screen.blit(image, (0, 0))
        screen.blit(image2, (1*50, 0))
        label = font.render(f"blit: {image2.get_at((25, 25))}", True, "white", "black")
        screen.blit(label, (100, 00))
        label = font.render(f"original (left): {image.get_at((25, 25))}", True, "white", "black")
        screen.blit(label, (100, 25))

        screen.blit(image2, (0, 50))
        screen.blit(image3, (1*50, 50))
        label = font.render(f"blit + flag RGBA_MUL: {image3.get_at((25, 25))}", True, "white", "black")
        screen.blit(label, (100, 50))

        y_offset = 100
        for i, ff in enumerate(flags):
            flag, name = ff
            tinted = image.copy()
            color = (255, 0, 0, 100)
            tinted.fill(color, None, flag)
            screen.blit(tinted, (50, i * 50 + y_offset))
            screen.blit(image2, (0, i*50+y_offset)) # original to compare to
            label = font.render(f"fill using flag {name}: {tinted.get_at((25, 25))}", True, "white", "black")
            screen.blit(label, (100, i*50+y_offset))

    pygame.quit()


if __name__ == '__main__':
    main()