My apologies, you're right Charlie, it is possible that SDL_Delay could be implemented in a way that would have an error.
Here's the unix source: http://www.libsdl.org/cgi/viewvc.cgi/branches/SDL-1.2/src/timer/unix/SDL_systimer.c?revision=2608&view=markup It looks like if HAVE_NANOSLEEP is defined, it uses timespec, which holds signed values (long), so the line "elapsed = now - then;" can result in a negative value for elapsed. Combined with the fact that ms (the time to wait) is unsigned, means that this set of code is bad: if ( elapsed >= ms ) { break; } ms -= elapsed; cause that line will make ms become a very high value... compared to when HAVE_NANOSLEEP is not defined, it would use unsigned int for elapsed, in which case the "if (elapsed >= ms)" line should hit and break, and not wait too long. So it looks like maybe the problem is just with HAVE_NANOSLEEP defined on unix/linux when building SDL? so maybe not using HAVE_NANOSLEEP would be a workaround? --- also, looking at pygame code, it seems to use signed vals for all it's calculations, and makes sure not to call SDL_Delay with a value below 0, so it looks to me like the pygame code should be OK. On Fri, Jun 27, 2008 at 1:34 PM, Charlie Nolan <[EMAIL PROTECTED]> wrote: > Actually, *YES*, I checked, it is true that "the relevant source is in > SDL". As I thought, SDL_Delay is not a simple sleep(ms) call, it's > got its own loop, functionally identical to the one I gave, excepting > only that the relevant calls are low-level. Don't believe me? Grab a > copy of the SDL source, go into src/timer/unix/SDL_systimer.c and > scroll down to line 112, which is where the loop starts. > > I will grant, there are plenty of other code paths based on the > intricacies of what's available on your system. I don't have the time > or the patience to go check all of them out, but I'd wager that they > use the same basic structure. > > -FM > > On Fri, Jun 27, 2008 at 3:16 PM, Brian Fisher <[EMAIL PROTECTED]> > wrote: > > It's not true that the relevant source is in SDL - clock.tick does call > > SDL_Delay, but all SDL_Delay takes a number of ticks to sleep, and then > just > > sleeps that long. It's pygame source that is deciding how long to > > sleep/wait. > > > > ... also no need to guess at the source, you can get at it from the web, > > even: > > > http://www.seul.org/viewcvs/viewcvs.cgi/trunk/src/time.c?rev=1240&root=PyGame&view=auto > > > > Basically, I think this could be fixed in pygame source without an SDL > > change, just by putting a max on how long to wait in clock tick - and > that > > delay could be maxed out at the framerate (surely you never would wait > > longer than 100ms to regulate a 10fps timer, right?) > > > > here's the relevant source (accurate_delay is passed in as 0, and the > > framerate arg is what was passed to tick): > > ---------------------------- > > > > // to be called by the other tick functions. > > static PyObject* > > > > clock_tick_base(PyObject* self, PyObject* arg, int use_accurate_delay) > > { > > PyClockObject* _clock = (PyClockObject*) self; > > float framerate = 0.0f; > > int nowtime; > > > > if (!PyArg_ParseTuple (arg, "|f", &framerate)) > > > > return NULL; > > > > if (framerate) > > { > > int delay, endtime = (int) ((1.0f / framerate) * 1000.0f); > > _clock->rawpassed = SDL_GetTicks () - _clock->last_tick; > > delay = endtime - _clock->rawpassed; > > > > > > /*just doublecheck that timer is initialized*/ > > if (!SDL_WasInit (SDL_INIT_TIMER)) > > { > > if (SDL_InitSubSystem (SDL_INIT_TIMER)) > > { > > RAISE (PyExc_SDLError, SDL_GetError ()); > > > > return NULL; > > } > > } > > > > if (use_accurate_delay) > > delay = accurate_delay (delay); > > else > > { > > // this uses sdls delay, which can be inaccurate. > > > > if (delay < 0) > > delay = 0; > > > > Py_BEGIN_ALLOW_THREADS; > > SDL_Delay ((Uint32) delay); > > Py_END_ALLOW_THREADS; > > } > > > > if (delay == -1) > > > > return NULL; > > } > > > > nowtime = SDL_GetTicks (); > > _clock->timepassed = nowtime - _clock->last_tick; > > _clock->fps_count += 1; > > _clock->last_tick = nowtime; > > if (!framerate) > > > > _clock->rawpassed = _clock->timepassed; > > > > if (!_clock->fps_tick) > > { > > _clock->fps_count = 0; > > _clock->fps_tick = nowtime; > > } > > else if (_clock->fps_count >= 10) > > > > { > > _clock->fps = _clock->fps_count / > > ((nowtime - _clock->fps_tick) / 1000.0f); > > _clock->fps_count = 0; > > _clock->fps_tick = nowtime; > > Py_XDECREF (_clock->rendered); > > > > } > > return PyInt_FromLong (_clock->timepassed); > > } > > > > > > >
