I am working on a image slider and using transitions in it. So, when I hit "next button" to get the next image in the middle of transition, the function gets called for next image, though the last transition affect hasn't done yet.
How should I stop the function to be called until the last transition completes? Please help! Thank You.
When I was working without transitions, it was working great but that wasn't smooth in mozilla, so I came up with transitions to make it! Now it is better than before but creating problems as transitions will take time to execute, and if in that time duration, I hit for next image, it calls the function for next transition effects.
What you are looking for is called 'debouncing'. If you can use an external library, I would recommend to use enter link description here. Underscore provides a similar function. This function ensures your function is not called twice and even can set a delay between two invocations.
If you can't then, you can google for a sample implementation like this one (I didn't test this one as I usually uses lodash's).
Hope this helps.
Related
I've built and ran the example at libsound.io.
The life cycle of SoundIoOutStream* outstream is not clear for me.
According to the example soundio_outstream_create(device) returns that pointer. Then soundio_outstream_open(outstream) and soundio_outstream_start(outstream) gets called. At this point the callback starts getting called.
Is there any way to stop the callback from getting called?
Is there any soundio function to "close" or "stop" outstream?
(I may edit or add to my questions based on the responses, right now I have too many unknowns to ask the right question.)
The important thing is that: we don't create a stream for each sound clip in the resources, we create a stream each time we want to play a sound clip.
After playing the sound clip, soundio_outstream_destroy(outstream); stops the callback from getting called. The trick is that we can't call this function within write_callback so we should implement some kind of messaging between callback thread and our app's thread to destroy outstream.
There are more details in my answer here: Play multiple streams with soundio
Hello I am looking for a signal for gtkmm. Basically I am doing some simulations and what I want is something like this :
I assume I do 5 simulations :
progressBar.set_fraction(0);
1 simulation
progressBar.set_fraction(progressBar.get_fraction()+1/5)
2 simulation
progressBar.set_fraction(progressBar.get_fraction()+1/5)
3 simulation
progressBar.set_fraction(progressBar.get_fraction()+1/5)
4 simulation
progressBar.set_fraction(progressBar.get_fraction()+1/5)
5 simulation
progressBar.set_fraction(progressBar.get_fraction()+1/5)
But I don't know which signal I have to use and how to translate to this.
Thank you a lot for your help !!!
The pseudo code which you presented in your question should actually work - no signal is necessary. However, you could introduce a signal into your simulation for update of the progress bar. IMHO this will not solve your problem and I will try to explain why and what to do to solve it:
You provided a little bit too less context, so, that I will introduce some more assumptions: You have a main window with a button or toolbar item or menu item (or even all of them) which start the simulation.
Let's imagine you set a breakpoint at Gtk::ProgressBar::set_fraction().
Once the debugger stopped at this break point you will find the following calls on the stack trace (probably with many other calls in between):
Gtk::Main::run()
the signal handler of the widget or action which started the simulation
the function which runs the five simulations
and last the call of Gtk::ProgressBar::set_fraction().
If you could inspect the internals of Gtk::ProgressBar you would notice that everything in Gtk::ProgressBar::set_fraction() is done properly. So what's wrong?
When you call Gtk::ProgressBar::set_fraction() it probably generates an expose event (i.e. adds an event to the event queue inside of Gtk::Main with a request for its own refresh). The problem is that you probably do not process the request until all five runs of the simulation are done. (Remember that Gtk::Main::run() which is responsible for this is the uppermost/outmost call of my imaginery stack trace.) Thus, the refresh does not happen until the simulation is over - that's too late. (Btw. the authors of Gtk+ stated somewhere in the manual about their cleverness to optimize events. I.e. there might be finally only one expose event for the Gtk::ProgressBar in the event queue but this does not make your situation better.)
Thus, after you called Gtk::ProgressBar::set_fraction() you must somehow flush the event queue before doing further progress with your simulation.
This sounds like leaving the simulation, leaving the calling widget signal handler, returning to Gtk::Main::run() for further event processing and finally coming back for next simulation step - terrible idea. But we did it much simpler. For this, we use essentially the following code (in gtkmm 2.4):
while (Gtk::Main::events_pending()) Gtk::Main::iteration(false);
(This should hopefully be the same in the gtkmm version you use but if in doubt consult the manual.)
It should be done immediately after updating the progress bar fraction and before simulation is continued.
This recursively enters (parts of) the main loop and processes all pending events in the event queue of Gtk::Main and thus, the progress bar is exposed before the simulation continues. You may be concerned to "recursively enter the main loop" but I read somewhere in the GTK+ manual that it is allowed (and reasonable to solve problems like this) and what to care about (i.e. to limit the number of recursions and to grant a proper "roll-back").
What in your case is the simulation we call in general long running functions. Because such long running functions are algorithms (in libraries for anything) which shall not be polluted with any GUI stuff, we built some administrational infra structure around this basic concept including
a progress "proxy" object with an update(double) method and a signal slot
a customized progress dialog which can connect a signal handler to such a progress object (i.e. its signal slot).
The long running function gets a progress object (as argument) and is responsible to call the Progress::update() method in appropriate intervals with an appropriate progress factor. (We simply use values in the range [0, 1].)
One issue is the interval of calling the progress update. If it is called to often the GUI will slow down your long running function significantly. The opposite case (calling it not often enough) results in less responsiveness of GUI. Thus, we decided for more often progress update. To lower the time consuming of GUI, we remember the time of last update in our progress dialog and skip the next refreshs until a certain duration since last refresh is measured. Thus, the long running function has still some extra effort for progress update but it is not recognizable anymore. (A good refresh interval is IMHO 0.1 s - the perception threshold of humans but you may choose 0.05 s if in doubt.)
Flushing all pending events results in processing of mouse events (and other GTK+ signals) also. This allows another useful feature: aborting the long running function.
When the "Cancel" button of our progress dialog is pressed it sets an internal flag. If the progress is updated next time it checks the flag. If the flag became true it throws a special exception. The throw aborts the caller of the progress update (the long running function) immediately. This exception must be catched in the signal handler of the button (or whatever called the long running function). Otherwise, it would "fall through" to the event dispatcher in Gtk::Main where it is catched definitely which would abort your application. (I saw it often enough whenever I forgot to catch.) On the other hand: catching the special exception tells clearly that the long running function has been aborted (in opposition to ended by regulary return). This may or may not be something which can be stated on GUI also.
Finally, the above solution can cause another issue: It enables to start the simulation (via GUI) while a simulation is already running. This is possible because button presses for simulation start could be processed while in progress update. To prevent this, there is actually a simple solution: set a flag at start of simulation in the GUI until it has finished and prevent further starts while the flag is set. Another option can be to make the widget/action insensitive when simulation is started. This topic becomes more complicated if you have multiple distinct long running functions in your application which may or may not exclude each other - leads to something like an exclusion matrix. Well, we solved it pragmatically... (but without the matrix).
And last but not least I want to mention that we use a similar concept for output of log views (e.g. visual logging of infos, warnings, and errors while anything long running is in progress). IMHO it is always good to provide some visual action for end users. Otherwise, they might get bored and use the telephone to complain about the (too) slow software which actually steals you the time to make it faster (a vicious cycle you have to break...)
If you've ever used XNA game studio 4 you are familiar with the update method. By default the code within is processed at 60 times per second. I have been struggling to recreate such an effect in c++.
I would like to create a method where it will only process the code x amount of times per second. Every way I've tried it processes all at once, as loops do. I've tried for loops, while, goto, and everything processes all at once.
If anyone could please tell me how and if I can achieve such a thing in c++ it would be much appreciated.
With your current level of knowledge this is as specific as I can get:
You can't do what you want with loops, fors, ifs and gotos, because we are no longer in the MS-DOS era.
You also can't have code running at precisely 60 frames per second.
On Windows a system application runs within something called an "event loop".
Typically, from within the event loop, most GUI frameworks call the "onIdle" event, which happens when an application is doing nothing.
You call update from within the onIdle event.
Your onIdle() function will look like this:
void onIdle(){
currentFrameTime = getCurrentFrameTime();
if ((currentFrameTime - lastFrameTime) < minUpdateDelay){
sleepForSmallAmountOfTime();//using Sleep or anything.
//Delay should be much smaller than minUPdateDelay.
//Doing this will reduce CPU load.
return;
}
update(currentFrameTime - lastFrameTime);
lastFrameTime = currentFrameTime;
}
You will need to write your own update function, your update function should take amount of time passed since last frame, and you need to write a getFrameTime() function using either GetTickCount, QueryPerformanceCounter, or some similar function.
Alternatively you could use system timers, but that is a bad idea compared to onIdle() event - if your app runs too slowly.
In short, there's a long road ahead of you.
You need to learn some (preferably cross-platform) GUI framework, learn how to create a window, the concept of an event loop (can't do anything without it today), and then write your own "update()" and get a basic idea of multithreading programming and system events.
Good luck.
As you are familiar with XNA then i assume you also are familiar with "input" and "draw". What you could do is assign independant threads to these 3 functions and have a timer to see if its time to run a thread.
Eg the input would probably trigger draw, and both draw and input would trigger the update method.
-Another way to handle this is my messages events. If youre using Windows then look into Windows messages loop. This will make your input, update and draw event easier by executing on events triggered by the OS.
In my project i'm running a train which stops moving when it reaches a particular point this moving is carried out by glutTimerFunc .I once again want the train to start from the location where i click my mouse to a particular location
BUT THE PROBLEM HERE IS,
My timer still running even after reaching that location,so even when i initialise the starting point its not working(it continues from the left location).
Now i need to stop the timer and start the train timer for the new location.
The API documentation has the following to say:
There is no support for canceling a registered callback. Instead, ignore a callback based on its value parameter when it is triggered.
So, add a boolean to your software and ignore the event whenever it is triggered. It would be better to use a clock-based timer rather than an event-driven timer and do your timed updates manually everytime the main loop runs (you detect the amount of time since the last update, and you determine whether to perform an update tick(s)), in the long run however. This is how physics and various other time-based simulations are handled in most professional software, using the event-driven model sets you up to miss or frequently wind up handling a timed event excessively late.
Welcome to the world of game engines and actors.
My recommendation is that you don't try to do this by turning glutTimerFunc on or off directly. The timer function should be the top level "heartbeat" for the entire program, and it's job is just to tell every object that has behaviour - an "actor" - that it should update itself. The train should have its own internal state that knows where it is and whether it should be moving or not.
I'v always wondered how this works. Does having more slow down the game? for example how would one represent checking if a car has flipped. It could be seen as:
if (player.car.angle.y == 180)
{
do something
}
The parts that puzzle me is, when would the game check for it? The way I see it, every thing that can happen in the game seems to evolve an if. I'm just wondering how these are handled.
Also, since the game runs through a loop, what if the car is flipped for more than 1 frame, would a Boolean really be used to check if the event has been fired
Thanks
In most general terms, any object in an engine has a state - if it changes state (e.g. not flipped to flipped), that is a transition.
From a transition you can fire an event or not, but as the transition does only occur when changing state the event won't be fired more then once.
As for the conditions that trigger the transitions, they have to be coded somewhere of course. Sometimes they are more explicitly coded, but mostly they are parameterized so that scripts or some sort of configuration can change them easily.
How it is implemented in the end differs broadly, it depends on the libraries that are used as well the engine design itself.