Sdl event loop

Hi folks! Input is vital to the game playing experience for the following reasons:. The code above initializes the SDL video mode, and creates a small window which can accept keyboard input when it has focus. Now on to the useful stuff:. When an event has occurred however, the code within the inner while loop will be executed. Of interest to us now are the following type values:.

The result is displayed with printf. The SDLMod value is then compared to a number of possible keypress modifier constants to determine which if any are currently valid. The DisplayStateDisplayModifiers and DisplayKey functions will give use a nice description of which keys have been pressed, how they were pressed, and what modifiers were applied.

Look for a stdout. Joel Longanecker's Keyboard Tutorial. Sign In Don't have an account? Start a Wiki. Input is vital to the game playing experience for the following reasons: People do not enjoy games that play themselves.

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People want something to happen when they mash the keyboard in anger. For these reasons, and moreI suggest you read on! Categories :. Cancel Save.Last time we added audio support by taking advantage of SDL's audio functions. SDL started a thread that made callbacks to a function we defined every time it needed audio. Now we're going to do the same sort of thing with the video display. This makes the code more modular and easier to work with - especially when we want to add syncing.

So where do we start? First we notice that our main function is handling an awful lot: it's running through the event loop, reading in packets, and decoding the video. So what we're going to do is split all those apart: we're going to have a thread that will be responsible for decoding the packets; these packets will then be added to the queue and read by the corresponding audio and video threads. The audio thread we have already set up the way we want it; the video thread will be a little more complicated since we have to display the video ourselves.

We will add the actual display code to the main loop. But instead of just displaying video every time we loop, we will integrate the video display into the event loop. When we finally sync the video in the next tutorial, it will be a simple matter to add the code that will schedule the next video refresh so the right picture is being shown on the screen at the right time. We're also going to clean up the code a bit.

We have all this audio and video codec information, and we're going to be adding queues and buffers and who knows what else. All this stuff is for one logical unit, viz. So we're going to make a large struct that will hold all that information called the VideoState. First we see the basic information - the format context and the indices of the audio and video stream, and the corresponding AVStream objects.

Then we can see that we've moved some of those audio buffers into this structure. We've added another queue for the video, and a buffer which will be used as a queue; we don't need any fancy queueing stuff for this for the decoded frames saved as an overlay. The VideoPicture struct is of our own creations we'll see what's in it when we come to it.

We also notice that we've allocated pointers for the two extra threads we will create, and the quit flag and the filename of the movie.

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So now we take it all the way back to the main function to see how this changes our program. Then we'll initialize our locks for the display buffer pictqbecause since the event loop calls our display function - the display function, remember, will be pulling pre-decoded frames from pictq.

At the same time, our video decoder will be putting information into it - we don't know who will get there first. Hopefully you recognize that this is a classic race condition. So we allocate it now before we start any threads. Let's also copy the filename of our movie into our VideoState. This will in turn call the video refresh function when we see it in the event queue. It will also pass that function user-defined data.

The first half of the function has nothing new; it simply does the work of opening the file and finding the index of the audio and video streams. The only thing we do different is save the format context in our big struct. This is a pretty natural way to split things up, and since we do a lot of similar things to set up the video and audio codec, we reuse some code by making this a function.

This is where we would also insert other options, such as forcing the codec instead of autodetecting it and so forth. Notice that instead of aCodecCtx, we've set up our big struct as the userdata for our audio callback. We also have added our video queue and set it up in the same way we set up our audio queue. Most of the point is to launch the video and audio threads. The format context has a ByteIOContext struct inside it called pb. ByteIOContext is the structure that basically keeps all the low-level file information in it.

After our for loop, we have all the code for waiting for the rest of the program to end or informing it that we've ended. This code is instructive because it shows us how we push events - something we'll have to later to display the video.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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sdl event loop

Every time I run the game, it crashes without errors or anything in the compiler debug window. It doesn't crash immediately or consistently, sometimes taking 10 seconds to crash and other times taking 2 minutes to crash. When I played around with return values at the end of the main function it turned out it wasn't crashing, but rather quitting as the return values were consistent with what I changed it to. The only theory that I have is that my poll event loop is glitching and telling the program to quit when it isn't supposed to.

Is it possible that when the mouse moves or clicks, that it is confusing it for exiting? I don't think the ram is overloading either because it only displays what it needs to tile-wise. Because in your code you check keysym for all events, so usually event is of wrong type when you test if it is escape, and you get "garbage" value for keysym, and sometimes it matches with ESC. Learn more.

SDL event loop quitting? Ask Question. Asked 7 years, 1 month ago. Active 10 months ago. Viewed 7k times. Scott Sellers 3, 3 3 gold badges 21 21 silver badges 40 40 bronze badges. Blake Doeren Blake Doeren 1 1 gold badge 7 7 silver badges 16 16 bronze badges. I think it's ok. Not really problem in your code. We need more code. I guess you may be overflowing a buffer or something in the stack, deep in your function call graph, and the event struct gets corrupted.

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Sometimes, by chance, the event. Active Oldest Votes.

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How about changing the switch at end of your snippet to: if event. Actually might be good idea to test the event.

Yes as it turns out, after setting up some breakpoints the escape key was triggering without me pressing it! All I need to do now is adjust it so that the escape key is checked more carefully. Any type of event that has the same value as the Escape key would trigger your code to quit.Event Driven Programming.

In our code after SDL is initialized and the media is loaded as mentioned in the previous tutorialwe declare a quit flag that keeps track of whether the user has quit or not. Since we just started the application at this point, it is obviously initialized to false.

A SDL event is some thing like a key pressmouse motionjoy button pressetc. In this application we're going to look for quit events to end the application. In the previous tutorials, we had the program wait for a few seconds before closing. In this application we're having the application wait until the user quits before closing. So we'll have the application loop while the user has not quit.

This loop that keeps running while the application is active is called the main loop, which is sometimes called the game loop.

It is the core of any game application. At the top of our main loop we have our event loop. What this does is keep processing the event queue until it is empty. When you press a key, move the mouse, or touch a touch screen you put events onto the event queue.

After we're done processing the events for our frame, we draw to the screen and update it as discussed in the previous tutorial.

Writing An SDL2 Game Loop

If the quit flag was set to true, the application will exit at the end of the loop. If it is still false it will keep going until the user Xs out the window.

sdl event loop

Download the media and source code for this tutorial here. Back to SDL Tutorials.The first change we need to make is to load our new image to display a prompt for input. Grab it below and use our loadTexture function to load it up as we did previously. The structure of this loop will be very basic. If we were to start our program and then resize the window, click the mouse and press a key the event queue would look like this.

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I encourage you to read the docs and check it out later! So our event processing loop could look like this. The final part of our main loop will take care of rendering our scene using the same methods as before. When we combine this with our event handling code our basic main loop becomes:.

When you run the program you should be able to quit by closing the window, pressing any key or clicking the mouse. Extra Fun: How could we move the image around?

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What about moving based on key input? Completing the Main Loop The final part of our main loop will take care of rendering our scene using the same methods as before. End of Lesson 4 When you run the program you should be able to quit by closing the window, pressing any key or clicking the mouse.Running SDL in secondary thread bigfoot I have a main thread which conditionally blocks, so I need to run my SDL app in a secondary thread.

sdl event loop

In the run of the secondary thread, I put my SDL init, video initialization and event loop which also does a render. I pause milliseconds in each iteration. The OpenGL graphics seems to display fine, but I am not receiving any mouse or keyboard events from the window This is my first application using SDL, so I am not sure if there is any special consideration needed for running in a secondary thread. If I put my same SDL code into the main thread, everything works fine.

Could someone give me a pointer or two on how to solve this problem? I don't think this use case is supported. At least some time ago it was not. The main thread on some systems, at least in the past, was special for some purposes, and some things probably won't work. Maybe a different SDL video back-end will produce different results? In general, you never want to run a second thread on OSX for anything to do with Cocoa, Cocoa is not thread safe and very prone to crashing if you are not careful, I ran into many issues on QuakeLive with this approach which does use a second thread for the game window.

Not a single Cocoa function is thread-safe, so you must use mutex blocking around all Cocoa calls, even closing a window will crash if other Cocoa calls are occurring. To understand why, read up on the event loop and memory pools, but here's the basic concept: there is a "memory pool" which groups allocations for easy freeing all at once, the main event loop empties this pool every iteration to get rid of stale event processing data, so if something is still using that data in another thread you get a crash, intriguingly most of the window management functions also allocate from this pool so if it is freed during their use, you get a crash So you have to block the main thread whenever you call Cocoa functions from your secondary thread It's fairly painful.

X11 can accommodate threaded calls but you have to call a function to enable threading I believe, but be aware that the events come in on the event loop thread, so your event handling will be running on that thread, and thus you need some blocking to keep that from messing up your other thread. Windows accommodates threaded calls by default, but be aware that your events come in on the event handling thread same considerations as above.

Whilst AppKit isn't exactly thread-friendly, Foundation the other half of Cocoa is perfectly happy to be multi-threaded, hence the built-in mechanisms like NSThread and friends. Alistair On 19 MayatForest Hale wrote: Quote: In general, you never want to run a second thread on OSX for anything to do with Cocoa, Cocoa is not thread safe and very prone to crashing if you are not careful, I ran into many issues on QuakeLive with this approach which does use a second thread for the game window.

Quote: I have a main thread which conditionally blocks, so I need to run my SDL app in a secondary thread. Thanks everyone for the expert help. We are refactoring so that our event loop can be in the main thread. Posted: Tue May 18, pm. Donny Viszneki Guest.

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Eric Wing Guest. Kenneth Bull Guest. Posted: Wed May 19, am. So generally speaking, if you want to use threading, you'll need to factor your code in such a way that the unsafe things are always performed on the main thread. Forest Hale Guest. Alistair Lynn Guest. Posted: Wed May 19, pm. Mason Wheeler Guest. Nathaniel J Fries Joined: 30 Mar By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Is there a way to do this or do you guys have a better idea? The name keyEvent is misleading. Refactor your code similar to many examples available on the web at sourceforge, or at molly rocket, or just google it. Learn more.

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Ask Question. Asked 9 years, 4 months ago. Active 8 years, 8 months ago. Viewed times. I'm a bit of a newbie so please be specific. Lemmons Lemmons 1, 4 4 gold badges 20 20 silver badges 30 30 bronze badges. NEVER wait for an event. Let the events come to you. Active Oldest Votes. I'll hit that silly X and it won't quit.

Lemmons: No idea if there's something special you have to do in Windows, but I would be surprised. Works fine for me in X Better changes: Refactor your code similar to many examples available on the web at sourceforge, or at molly rocket, or just google it. Nobody 8, 2 2 gold badges 33 33 silver badges 82 82 bronze badges.

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