The SDL forums have moved to discourse.libsdl.org.
This is just a read-only archive of the previous forums, to keep old links working.

Hi Guys,             I have some issues with opengl and sdl, the first issue is switching from windowed to full screen and vice versa , get some all black textures, and the second more pressing issue, is i am getting tearing on my large sprite movements , i did have the move stuff in a timer and the draw stuff in the main loop, even if i tell it all to move after my flip it does not make much odds.


at the moment I'm doing this at the end of my main loop 


               DrawEverything();
       this_tick = SDL_GetTicks();
if ( this_tick < next_tick ) 
{
  SDL_Delay(next_tick-this_tick);
}
next_tick = this_tick + (1000/FRAMES_PER_SEC);
SDL_GL_SwapBuffers();
MoveEverything(0, NULL);


is this correct as i have ported my old 2D SDL code?, i draw everything to gScreen which is the output from SDL_SetVideoMode(... but i am obviously not getting double buffering even on SDL_FULLSCREEN with 


SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );


so how could i make my own double buffering ie Draw to one screen, copy it to the other and flip or swap and flip... any help much appreciated


Trish

1) Last time I checked, on most platforms the GL context is completely
lost when switching between windowed and full screen. To be sure you
won't lose everything you have to recreate everything after switching
(textures, etc.).

2) To reduce tearing you have to enable vertical blank syncing. Double
buffering is good towards reducing tearing, but not enough by itself
because the actual "physical" redraws can still happen while a frame
is in the middle of being thrown to the screen, which is what causes
tearing. The attribute you need is SDL_GL_SWAP_CONTROL. Keep in mind
your platform may not support it, though. Most video drivers (AMD and
nVidia, on Windows or Linux) also allow you to force vsync on all
OpenGL viewports, so you can try that too.
--
- SR

On Mon, Sep 14, 2009 at 16:01, Patricia Curtis
wrote:
_______________________________________________
SDL mailing list

http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

Thats one alternative!
In my code I put a rest(1) (on windows I need to use timeBeginPeriod to set the timer precision to 1 ms ) after the SDL_GL_SwapBuffers, so if there is no vsync support it wont take all CPU, it will consume more CPU than a PC that supports vsync (but not all CPU), but the game I am working on is full screen only, so it doesnt matter
Then I show a warning message saying that vsync could not be enabled.
So the game will run on different speeds from pc to pc? No! I dont use the fps to update my logic, I just use it to calc the time it takes every frame and make the lpf calculation (logics per frame), than the logic loop of the game will run 'lpf' times!

Something like this:

Game loop begin
- Start counting time / reset counting time
- Draw things
- SDL_GL_SwapBuffers and SDL_Delay(1)
- Get counted time and make calculation of lpf
- Update the logic 'lpf' times
Game loop end

The calculation would be something like this:

double lpfAux = 0; // Out of the Game loop scope
...

int elapsed = timer.elapsedTime(); // Do something to get the elapsed time up ther
lpfAux = (elapsed/LPS_WAIT); // LPS_WAIT = 1000/Logic per Second, its a double!!!
lpf = (int)lpfAux; // Convert it to int and put on lpf
lpfAux -= lpf; // Lets subtract from lpfAux, its to accurate the lpf calculation, elapsed/LPS_WAIT wont give us a integer number
...

for (int x = 0;x < lpf;x++)
// Logic loop
...

You can choice the best alternative that fits in your game! You only need to update the logic of your game uniformly not depending on a fix FPS value! Of course only if you intend to use vsync which I think its a great advantage. (it can have some small errors, like on one second it update 1002 times, so on the other second it will update 998 times, there are other techniques, like delta time)

Bruno

Você sabia que pode utilizar o Messenger de qualquer tipo de celular? Saiba mais.

Well you should never rely on vsync for managing game logic time anyway.
A properly written game logic loop will work fine regardless of the
presence of vsync or not. At worst vsync will create some minor
overhead due to the extraneous sleeps.
--
- SR

On Tue, Sep 15, 2009 at 15:35, Bruno Adami wrote:
_______________________________________________
SDL mailing list

http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

Hello,

When an SDL window is resized or switched between fullscreen/windowed modes
it will destroy and recreate the OpenGL context. You will need to reload
your textures into video memory which is why you are seeing a black screen.

Not sure about the tearing problem. Maybe something to do with vsync being
enabled/disabled? Just a guess though.

Good luck,
Kiaran



Patricia Curtis-2 wrote:

--
View this message in context: http://www.nabble.com/SDL-and-OpenGL-Issues-tp25442541p25445086.html
Sent from the SDL mailing list archive at Nabble.com.

_______________________________________________
SDL mailing list

http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

Thanks for your help guys, its all sorted now, the black textures were
an issue with my texture creator, and i have adopted a combination of
your responses for the vblank issue

SDL_GL_SwapBuffers();
StartTicks = EndTicks;
EndTicks = SDL_GetTicks();
DeltaTick = ((EndTicks - StartTicks) / 15.0);
RunTransition(); // this code use the DeltaTick as an multiplier for
the movements of the front end eg
// ScrollPos++; is now
ScrollPos+=(1*DeltaTick);

// now because there were too many changes needed in the animation
code (game 90% complete)
// i go through my animation loop a number of times depending how
slow the last frame was

while(AnimationTimes>1)
{
AnimationLoop(0, NULL);
AnimationTimes--;
}
AnimationTimes+=DeltaTick;

obviously i set the tick counts up before my main loop

StartTicks = SDL_GetTicks();
EndTicks = SDL_GetTicks();
DeltaTick = (double)((EndTicks - StartTicks) / 15.0);

also if i do a load of an image during my main loop i reset the
counters after the load so there are no large jumps in the frame rate

StartTicks = SDL_GetTicks();

Thanks a million
_______________________________________________
SDL mailing list

http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org