Re: [pygame] Another blitting surface to itself crash

["Nicholas Dudfield" <ndudfield@xxxxxxxxx>]

I had a little play with the test_blit_to_self.py: 

SDL VERSION:

1.2.13 prebuilts

PYGAME:

Mingw compiled, svn r 1619

OBSERVATIONS:

Unmodified the test wouldn't run at all as noted earlier.

I don't know if it's any help but I noticed after commenting out the "blitting screen to self" section that I could get the "blitting surface to self" test and "blitting surface to screen" to run the full 100 cycles if I instantiated the Surface `a` with pygame.SRCALPHA flags.

Also, if using BLEND_RGB_ADD flags "blitting screen to self" worked. Also screen.copy() worked as a source... but eh.

CONCLUSIONS:

s.blit(s, (0,0)) works if SRCALPHA bits set for s
screen.blit(screen, step, None, pygame.BLEND_RGB_ADD)

Is that any help for you guys in debugging?? I have no C-fu or I would have a tinker myself.

Cheers.

ps... attached modified version of test with "use alpha blit" changes


pps.

This is in surface.c around line 1996.... ??

    /* see if we should handle alpha ourselves */
    if (dst->format->Amask && (dst->flags & SDL_SRCALPHA) &&
        !(src->format->Amask && !(src->flags & SDL_SRCALPHA)) &&
        /* special case, SDL works */
        (dst->format->BytesPerPixel == 2 || dst->format->BytesPerPixel == 4))
    {
        result = pygame_AlphaBlit (src, srcrect, dst, dstrect, the_args);
    }
    else if (the_args != 0)
    {
        result = pygame_Blit (src, srcrect, dst, dstrect, the_args);
    }
    else
    {
        result = SDL_BlitSurface (src, srcrect, dst, dstrect);
    }

import pygame
import random
import math
import sys

print pygame.get_sdl_version()

# pygame.FULLSCREEN    #create a fullscreen display
# pygame.DOUBLEBUF     #recommended for HWSURFACE or OPENGL
# pygame.HWSURFACE     #hardware accelerated, only in FULLSCREEN
# pygame.OPENGL        #create an opengl renderable display
# pygame.RESIZABLE     #display window should be sizeable
# pygame.NOFRAME       #display window will have no border or controls

screen = pygame.display.set_mode((800, 600))

num_runs = 100
scroll_step = 100
for i in xrange(num_runs):
    print "pass",i
    test_width = random.randint(10,400)
    test_height = random.randint(10,400)
    
    # An optional special flags is for passing in new in 1.8.0: BLEND_ADD,

    # BLEND_SUB, BLEND_MULT, BLEND_MIN, BLEND_MAX new in 1.8.1:
    # BLEND_RGBA_ADD, BLEND_RGBA_SUB, BLEND_RGBA_MULT, BLEND_RGBA_MIN,
    # BLEND_RGBA_MAX BLEND_RGB_ADD, BLEND_RGB_SUB, BLEND_RGB_MULT,
    # BLEND_RGB_MIN, BLEND_RGB_MAX With other special blitting flags
    # perhaps added in the future.

    a = pygame.Surface((test_width, test_height), pygame.SRCALPHA)

    a.fill((random.randint(0,255), random.randint(0,255), random.randint(0,255)))
    try:
        pygame.draw.line(a, (255,255,255), (0,0), (test_width, test_height), 10)
    except:
        pass
    print "blitting surface to self"
    sys.stdout.flush()
    a.blit(a, (random.randint(-test_width, test_width), random.randint(-test_height, test_height)))

    angle = (2.0*math.pi*i)/num_runs
    step = (math.cos(angle)*scroll_step, math.sin(angle)*scroll_step)
    print "blitting screen to self"
    sys.stdout.flush()
    screen.blit(screen, step, None, pygame.BLEND_RGB_ADD)

    print "blitting surface to screen"
    sys.stdout.flush()
    screen.blit(a, (random.randint(-test_width, 800), random.randint(-test_height, 600)))
    pygame.event.get()
    pygame.display.flip()