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Updating and Drawing Problem in C++ And SDL


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#1 DarkHorseKnight   Members   -  Reputation: 143

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Posted 03 February 2012 - 01:09 PM

Hello I'm trying to get my game to update the screen and draw graphics on its own I kind of made it happen but it still flickers which you can see in this video I made just too showcase this problem

http://www.youtube.com/watch?v=9j_ZDHr1x_8

Now I really don't know what is causing this its really strange if you look at the code you will know what I mean

http://pastebin.com/kvtaUqiM


and above is the code of which the problem lies



any suggestions,tips,ideas,reasons would be great! Posted Image

Sponsor:

#2 Zael   Members   -  Reputation: 154

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Posted 03 February 2012 - 03:53 PM

I don't see you call SDL_SetVideoMode anywhere to get the screen surface, but I would make sure you are using double buffering.

The problem is actually here though:

TestThread = SDL_CreateThread(DrawAndUpdate,NULL);
//Update Screen
SDL_Flip(Screen);


I don't know how SDL_Threads work (I have never used them), but it looks to me like you are creating a new thread in every loop (which is bad for performance). It also looks like you never join or detach the thread, which makes me think you are leaking memory like nobody's business.

But the thing that is causing your particular problem is that you are flipping the screen in the main thread when DrawAndUpdate is happening in another thread. If DrawAndUpdate is only half done when SDL_Flip is called, you will only get half of your sprites on the screen. Without any sort of controls in place the behavior here is completely random. On some loops it will work fine, in others nothing will be copied before the screen flip. In short, put all your drawing code (including SDL_Flip) in a single thread, or at least wait until the drawing thread is finished before flipping the screen.

#3 DarkHorseKnight   Members   -  Reputation: 143

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Posted 03 February 2012 - 04:18 PM

Oh thank god! Posted Image at leasts that's fixed I will remember now to draw and update in the same thread for anything that is art related but there is another problem the game lags on every movement of all objects on the screen accept the cloud for some reason.

I think its because of the drawing taking alittle while to blit ? would I be correct on that or wrong?

heres my code with the changes

http://pastebin.com/1hQjgZJN

I also tried what you said but in a different way where I put all blits and sdl_flip into the main while loop and then the same thing occurred so I assumed it was wrong and went back to threads you see

#4 Zael   Members   -  Reputation: 154

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Posted 03 February 2012 - 04:45 PM

No... The number of objects you are currently drawing should easily go at >60fps on modern processors at that resolution. I am not sure what lag you refer to by just looking at the code; however, if I recall correctly (been a while since I have done anything with SDL) the SDL_KEYDOWN event is only triggered when the key is first pressed, so none of that code occurs when the key is held down until Windows (or other OS) enables key repeat. In other words right now, you are looking at the key up/down events, but not the key up/down state. An event only happens during state change.

#5 DarkHorseKnight   Members   -  Reputation: 143

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Posted 03 February 2012 - 04:48 PM

I have //Enable Key Repeat
SDL_EnableKeyRepeat(10,SDL_DEFAULT_REPEAT_INTERVAL);

so what else could it be hmm I can't think of anything off the top of my head.

but I'm guessing its do with the order of my SDLK_RIGHT code but that's just a guess I'm probably wrong.

so what would be suggestible?

#6 BeerNutts   Crossbones+   -  Reputation: 2950

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Posted 03 February 2012 - 11:01 PM

My first suggestion is to stop trying to use multiple threads. You are going to cause more problems than you'll solve doing that, especially for a simple 2d game. Just do everything in the main thread, in typical game loop.

Getinput()
UpdateObjects()
DrawAllObjects()

Repeat.
My Gamedev Journal: 2D Game Making, the Easy Way

---(Old Blog, still has good info): 2dGameMaking
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"No one ever posts on that message board; it's too crowded." - Yoga Berra (sorta)

#7 DarkHorseKnight   Members   -  Reputation: 143

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Posted 04 February 2012 - 10:09 AM

Fixed thanks! :D




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