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Insectoid

Mon Jun 20, 2011 8:33 pm


SDL KEYUP event

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I've been messing around in SDL to get familiar with it (and also to get better at C++). Anyway, the issue I'm having is, the SDL_KEYUP event does not seem to work right. Or maybe I don't understand how event queues are handled. Either way, something's up.

	while (!quit){
		while (SDL_PollEvent (&eventQueue)) {
			if (eventQueue.type == SDL_QUIT) quit = true;
			else if (eventQueue.type = SDL_KEYDOWN){
				switch (eventQueue.key.keysym.sym){
					case SDLK_UP: p1.setDirectionUp();break;
					case SDLK_DOWN: p1.setDirectionDown();break;
					case SDLK_ESCAPE: quit = true;break;
				}
			}
			else if (eventQueue.type = SDL_KEYUP){
				switch (eventQueue.key.keysym.sym){
					case SDLK_UP: p1.setDirectionStop();break;
					case SDLK_DOWN: p1.setDirectionStop();break;
				}
			}
		}
//There's more code here, but I left it out 'cause I don't think it's the issue


The functions setDirectionUp(), setDirectionDown(), and setDirectionStop() all work perfectly (I've tested them rigorously). The SDL_KEYDOWN case works perfectly fine. I press 'up', my character moves up. If I press 'down', the character moves down. Note that these functions just change a direction flag. There is a move() function that actually moves the character. The SDL_KEYUP case calls SetDirectionStop() which sets the direction flag to 0 (ie no movement). This is not happening. 

When I remove the SDL_KEYDOWN case completely (comment that section out), SDL_KEYUP works sporadically. The event seems to trigger whenever there is a KEYDOWN, OR a KEYUP event. So, KEYUP *sort of* works. I think part of the issue is that maybe checking for SDL_KEYDOWN is bumping SDL_KEYUP off the event queue? 

I admit, I have very little understanding of how events work, and my implementation may well be the issue.

~Insectoid


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DemonWasp

Tue Jun 21, 2011 11:03 am


RE:SDL KEYUP event

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eventQueue.type = SDL_KEYDOWN

Look very closely at that condition and tell me what you see.


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Insectoid

Tue Jun 21, 2011 11:08 am


RE:SDL KEYUP event

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Ah, haha, my bad. Major logical flaws I usually catch myself, but tiny errors like these slip past me all too often.


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DemonWasp

Tue Jun 21, 2011 11:18 am


RE:SDL KEYUP event

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Depending on which compiler you're using, there's usually a setting to turn on errors for things like this. For gcc or g++ it's "-Wall".

I strongly recommend using "-Wall -Werror -Wextra", and I like to use "-pedantic" whenever I write C/C++/uC++. These will help you find minor syntax slip-ups before they get compiled and produce odd logic errors. If you're working with templates, it can be helpful to use "-Wfatal-errors", so that the very first problem halts compilation, preventing one error from visually merging with the next.

The price you pay for these settings is correcting your programs up-front, at compile time. The price you pay for NOT using them is difficult-to-debug logic errors at run-time.


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Insectoid

Tue Jun 21, 2011 12:06 pm


RE:SDL KEYUP event

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Hmm, I'm using Xcode on OS X at the moment, since I've not figured out how to link SDL manually, but I'm sure there's an option somewhere to turn on those flags (Xcode compiles with gcc I believe).


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DemonWasp

Tue Jun 21, 2011 12:33 pm


RE:SDL KEYUP event

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http://developer.apple.com/tools/xcode/xcodebuildsettings.html


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Insectoid

Tue Jun 21, 2011 12:57 pm


RE:SDL KEYUP event

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Oh, thanks! Spares me some time on Google (and Apple's awful (imo) website).