Re: [pygame] BUG: segfault when blitting surface to itself
On 11 Apr 2008 at 21:33, Marcus von Appen wrote: Is there some case where blitting a surface on itself might be desired or necessary? If not, I'll add a simple check that tests the passed surface on equality and let blit() throw an exception, if both are the same. Its also used by effects, as you can see at: http://www.pygame.org/pcr/meltdown/index.php And older games in pygame ( linki commes to mind, first release of magicor also, I fixed the last for that problem) also used them. claxo
Re: [pygame] BUG: segfault when blitting surface to itself
On Fri, Apr 11, 2008 at 12:33 PM, Marcus von Appen <[EMAIL PROTECTED]> wrote: > Is there some case where blitting a surface on itself might be desired > or necessary? If not, I'll add a simple check that tests the passed > surface on equality and let blit() throw an exception, if both are the > same. > That sounds great. This has come up multiple times on the list over the years, and it would be good if it didn't. As a cross-platform library, pygame should really be stopping users from doing things on one platform that can't work on other platforms, to encourage writing portable code.
Re: [pygame] BUG: segfault when blitting surface to itself
Marcus von Appen wrote: Is there some case where blitting a surface on itself might be desired or necessary? Scrolling? -- Greg
Re: [pygame] BUG: segfault when blitting surface to itself
On Apr 11, 2008, at 3:46 PM, David Muffley wrote: Is there some case where blitting a surface on itself might be desired or necessary? If not, I'll add a simple check that tests the passed surface on equality and let blit() throw an exception, if both are the same. Regards Marcus For scrolling (topdown RPG, in my case), I use a surface just larger than the screen to hold all my unmoving objects, tiles, trees, chests, etc, and keep a Rect for where to put that surface onto the screen. Whenever I move a tiles worth in any direction (lets say i move 32 pixels to the right), I need to blit the rect <32, 0, width, height> to <0, 0, width, height> and add the rightmost-visible tiles to it. My first idea was to blit the surface onto itself, but of course that blew up on me. My fix was to use two surfaces and just blit from one onto the other, switching between the two every time I need to add another row/column onto the screen. It's not really memory inefficient (I only keep one extra 672x512 surface and a pointer in memory), but it definitely wasn't straightforward, and took me a while longer than I expected to implement it. Blitting a surface onto itself would have been much simpler. Yeah, certainly "scrolling" is a general use-case for blitting a surface onto itself. I could also imagine some forms of composing with alpha channels. Both of these can certainly be done with two surfaces instead, but a self-blit would be more efficient. -Casey
Re: [pygame] BUG: segfault when blitting surface to itself
> > Is there some case where blitting a surface on itself might be desired > or necessary? If not, I'll add a simple check that tests the passed > surface on equality and let blit() throw an exception, if both are the > same. > > Regards > Marcus For scrolling (topdown RPG, in my case), I use a surface just larger than the screen to hold all my unmoving objects, tiles, trees, chests, etc, and keep a Rect for where to put that surface onto the screen. Whenever I move a tiles worth in any direction (lets say i move 32 pixels to the right), I need to blit the rect <32, 0, width, height> to <0, 0, width, height> and add the rightmost-visible tiles to it. My first idea was to blit the surface onto itself, but of course that blew up on me. My fix was to use two surfaces and just blit from one onto the other, switching between the two every time I need to add another row/column onto the screen. It's not really memory inefficient (I only keep one extra 672x512 surface and a pointer in memory), but it definitely wasn't straightforward, and took me a while longer than I expected to implement it. Blitting a surface onto itself would have been much simpler.
Re: [pygame] BUG: segfault when blitting surface to itself
On Fri, Apr 11, 2008 at 8:33 PM, Marcus von Appen <[EMAIL PROTECTED]> wrote: > On, Fri Apr 11, 2008, Hugo Arts wrote: > > > python version: 2.5.1 > > pygame version: 1.8 > > OS: Windows XP > > > > If you attempt to blit a surface to itself, python segfaults. Seems to > occur > > only on windows (tested on XP and Ubuntu). > > I understand there is no reason to do this, but it would seem more > > appropriate to throw an exception or something like that. > > > > script to reproduce: > > import pygame > > pygame.init() > > > > a = pygame.Surface((10, 10)) > > a.blit(a, (0, 0)) > > Is there some case where blitting a surface on itself might be desired > or necessary? If not, I'll add a simple check that tests the passed > surface on equality and let blit() throw an exception, if both are the > same. > > Regards > Marcus > I can't think of a reason to blit a sprite onto itself. And if you really want to, you could create a copy of the surface, and blit with that (though it would be less memory efficient). Hugo
Re: [pygame] BUG: segfault when blitting surface to itself
On, Fri Apr 11, 2008, Hugo Arts wrote: > python version: 2.5.1 > pygame version: 1.8 > OS: Windows XP > > If you attempt to blit a surface to itself, python segfaults. Seems to occur > only on windows (tested on XP and Ubuntu). > I understand there is no reason to do this, but it would seem more > appropriate to throw an exception or something like that. > > script to reproduce: > import pygame > pygame.init() > > a = pygame.Surface((10, 10)) > a.blit(a, (0, 0)) Is there some case where blitting a surface on itself might be desired or necessary? If not, I'll add a simple check that tests the passed surface on equality and let blit() throw an exception, if both are the same. Regards Marcus pgpispUNtqcQj.pgp Description: PGP signature
[pygame] BUG: segfault when blitting surface to itself
python version: 2.5.1 pygame version: 1.8 OS: Windows XP If you attempt to blit a surface to itself, python segfaults. Seems to occur only on windows (tested on XP and Ubuntu). I understand there is no reason to do this, but it would seem more appropriate to throw an exception or something like that. script to reproduce: import pygame pygame.init() a = pygame.Surface((10, 10)) a.blit(a, (0, 0)) Output: Fatal Python error: (pygame parachute) Segmentation Fault This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information.
