I am looking at trying to pause something in C++. Specifically a bullet you shoot in a space invaders game. Each time you press the UP key it fires a shot, I have been trying to find a way to pause it for a number of seconds before being able to fire again.
I've tried Sleep(); but it freezes the entire game rather than pauses the ability to press UP again.
Firing code
if (CInput::getInstance()->getIfKeyDownEvent(DIK_UP))
{
g_pGame->AddSprite(new CMissile(m_fX, m_fY+0.5*m_fH, 0.09, 0.9, 2));
}
Try taking the current time and then adding your delay to it. Store that in your shooting object. The next time through your program loop, if the current time is less than the time stored in the object, ignore the UP arrow.
Here are two simple ways to manage this.
When you fire a bullet, take the current system time and add the delay you want to it. If the player attempts to fire again while the current time is less than the variable you set, nothing happens.
Or, when you fire a bullet, set a timer variable to the delay you want. Each update, subtract delta time from the timer. When the timer is <=0, the user can fire.
Typically when you want to deal with real time seconds, you need something called delta time. Due to the inconsistency with frame rates, you need a way to measure real time. Typically you do this by counting the amount of time elapsed between frames. Here's an example of this implementation:
Source
int timeSinceStart = glutGet(GLUT_ELAPSED_TIME);
int oldTimeSinceStart = 0;
while( ... ) // main game loop
{
int timeSinceStart = glutGet(GLUT_ELAPSED_TIME);
int deltaTime = timeSinceStart - oldTimeSinceStart;
oldTimeSinceStart = timeSinceStart;
secondsSinceLastShot += deltaTime;
if (secondsSinceLastShot > shotTimer)
{
canShoot = true;
secondsSinceLastShot = 0;
}
if ( // press space or something )
{
canShoot = false;
// shoot
}
}
Note that this uses GLUT's implementation of a timer, but you need to implement that yourself (probably using clock()).
I've tried Sleep(); but it freezes the entire game rather than pauses the ability to press UP again.
Sleeping will freeze the thread, which is not what you want to do. However, sleep() is typically used in an implementation that contains delta time, usually sleep()ing for the amount of time elapsed between frames. For an example, see Lazy Foo's SDL tutorials
Ignore the fact that I linked to both OpenGL and SDL links, the principle is the same no matter the graphics library used.
Related
I'm building a tetris game and I need the pieces to fall every x seconds; something like:
while(true){
moveDown();
sleep(x)
}
The problem is, I need to be able to move the pieces left and right in the meantime, i.e., call a function while it's sleeping.
How can I do that in c++?
Both time and key presses can be events which can be used to wait on. On UNIXes you'd use something like poll() with a suitable time for timeout and the input device used to recognize key presses. On other systems there are similar facilities (I'm a UNIX persons and I have never worked on Windows specific stuff although it seems the Windows facilities are actually more flexible). Depending on the result of poll() (timeout or activity on the I/O device in that case) you'd do the appropriate action.
This problem is solvable in multiple ways (another idea that comes to mind is multithreading, but that seems overkill). One approach would be to keep track of the number of "game cycles" and execute some function every n-th cycle like this:
for(int32_t count{1};;count++)
{
if (!count % 5)
{
// do something every 5th cycle
}
// do something every cycle
sleep(x);
}
you can measure how much time has passed since last fall and move piece down after given amount and then reset counter. In pseudo-code it could look like this:
while(true)
{
counter.update();
if(counter.value() == fall_period)
{
move_piece_down();
couter.reset();
}
// rotate pieces
}
If you are using typical implementation of game loop your counter can just accumulate elapsed time since last frame.
I'm making a game in openGL and I want to spawn 2 enemies per second on the screen. The problem is, I'm calling the spawn function inside idle:
idle
{
// ...
world.spawnEnemy();
}
And then, in the spawnEnemy function:
void World::spawnEnemy()
{
Enemy newEnemy, newEnemy2;
float start;
start = glutGet(GLUT_ELAPSED_TIME);
// 1/2 a second passes
while ( (glutGet(GLUT_ELAPSED_TIME) - start) <= 500 )
{
;
}
// create enemy
newEnemy();
pushToEnemyList(newEnemy);
// another 1/2 second passes
while ( (glutGet(GLUT_ELAPSED_TIME) - start) <= 1000 )
{
;
}
// create enemy
newEnemy2();
pushToEnemyList(newEnemy2);
}
And this is not working, of course. Probably because idle is called everytime and I'm calling a function inside idle that waits for a certain amount of time to pass and then everything starts going wrong. The solution is to do the spawning in the idle function (without calling any function, doing all the logic inside idle), but I don't like this idea. I need to do more things in a certain number of time, for example, my enemies have guns and they will have to shoot n times every second. And if I do all of these directly inside of idle it will become a mess. So, basically, how do I make this work:
idle
{
// ...
world.spawnEnemy();
world.enemyShoot();
// another functionalities that depend on time
}
instead of this:
idle
{
// ...
// logic of spawnEnemy directly here in the idle function
// logic of enemyShoot directly here in the idle function
// logic of another functionalities that depend on time directly here in the idle function
}
There is quite a few ways to do this here the most common:
Measure elapsed time
Simply remember time of last spawn t0 and on each (idle) iteration get current time t. If t0+T<=t then spawn new enemy ans set t0=t. The T is the period of spawning in the same units as the measured time. In your case 500ms.
As mentioned OnIdle Event will take 100% of one CPU core for itself. To remedy this use Sleep(x); where x<<T that will ease up on the CPU load (even Sleep(1); will be a big difference).
To measure time use any OS routine you got available (with high enough accuracy) I am using PerformanceCounter on Windows but there are other alternatives like RDTSC etc ...
Timers
Modern messaging based OS provides timer function which will fire your event periodically (usually with ~1ms accuracy). Just study your API to implement it. Then you just spawn your enemy inside timer event without any other logic or timing code ...
In case you do not have any timers you can fake this by creating thread with code like this inside:
for (;!spawn_exit;)
{
if (spawn_enabled) spawn();
Sleep(T);
}
where volatile bool spawn_enabled=true,spawn_exit=false; are used to control the spawning and stop the thread (before App shutdown) But in this case be careful with multi threaded access in the spawn() function ...
I am currently developing a stimuli provider for the brain's visual cortex as a part of a university project. The program is to (preferably) be written in c++, utilising visual studio and OpenCV. The way it is supposed to work is that the program creates a number of threads, accordingly to the amount of different frequencies, each running a timer for their respective frequency.
The code looks like this so far:
void timerThread(void *param) {
t *args = (t*)param;
int id = args->data1;
float freq = args->data2;
unsigned long period = round((double)1000 / (double)freq)-1;
while (true) {
Sleep(period);
show[id] = 1;
Sleep(period);
show[id] = 0;
}
}
It seems to work okay for some of the frequencies, but others vary quite a lot in frame rate. I have tried to look into creating my own timing function, similar to what is done in Arduino's "blinkWithoutDelay" function, though this worked very badly. Also, I have tried with the waitKey() function, this worked quite like the Sleep() function used now.
Any help would be greatly appreciated!
You should use timers instead of "sleep" to fix this, as sometimes the loop may take more or less time to complete.
Restart the timer at the start of the loop and take its value right before the reset- this'll give you the time it took for the loop to complete.
If this time is greater than the "period" value, then it means you're late, and you need to execute right away (and even lower the period for the next loop).
Otherwise, if it's lower, then it means you need to wait until it is greater.
I personally dislike sleep, and instead constantly restart the timer until it's greater.
I suggest looking into "fixed timestep" code, such as the one below. You'll need to put this snippet of code on every thread with varying values for the period (ns) and put your code where "doUpdates()" is.
If you need a "timer" library, since I don't know OpenCV, I recommend SFML (SFML's timer docs).
The following code is from here:
long int start = 0, end = 0;
double delta = 0;
double ns = 1000000.0 / 60.0; // Syncs updates at 60 per second (59 - 61)
while (!quit) {
start = timeAsMicro();
delta+=(double)(start - end) / ns; // You can skip dividing by ns here and do "delta >= ns" below instead //
end = start;
while (delta >= 1.0) {
doUpdates();
delta-=1.0;
}
}
Please mind the fact that in this code, the timer is never reset.
(This may not be completely accurate but is the best assumption I can make to fix your problem given the code you've presented)
I am a beginner in programming and I started to create a game in C++ where the player disappears from the screen(he dies) when a rock hits it.
What can i do to put the player back on the screen after 2 seconds?
I have number of lifes(LifeNb) a function which delete the player from the screen(removePlayer) and a function that add the player on the screen(addPlayer).
How can i do this using ?
int time = std::clock()/1000;
if(the rock hit) {
number of lives --;
remove player;
if(time == 2)
add player;
}
It's something like this?
One way to do it: When your player dies, store the current time (plus two seconds) to a variable. On each iteration of the game's event loop, check to see if the current time is greater than or equal to the time in the variable. If it is, restore the player, and set the variable's value to (a very large value that the clock will never reach).
clock_t timer = clock();
if ((clock()/CLOCKS_PER_SEC)-(timer/CLOCKS_PER_SEC) >= 2)
player.add();
If you just want to wait two seconds, however, you could also use the system library function sleep() for two seconds.
The sleep() function will delay for a specified number of seconds before continuing execution. It seems to be what you are looking for.
See here: http://pubs.opengroup.org/onlinepubs/009604599/functions/sleep.html
How would you wait a frame in c++.
I don't want the program to sleep or anything.
It would go soemthing like
Do this in this frame (1)
Continue with rest of program
Do this in the next frame (2)
where action 1 happens only in the first frame and action 2 happens only in the next frame. It would continue like this. 1, 2, 1 again, 2
I have the time between frames, I use c++ and i'm using Visual Studio 2008 to compile.
Edit:
I'm using Opengl my OS is Windows 7.
Frame - http://en.wikipedia.org/wiki/Frame_rate
like each image of the scene printed to the screen over a given time period
I'm making some assumptions here.
Suppose you have a model for which you wish to show the state. You might wish to maximise the CPU time spent evolving the model rather than rendering.
So you fix the target frame rate, at e.g. 25 fps.
Again, assume you have optimised rendering so that it can be done in much less than 0.04 seconds.
So you might want something like (pseudo-code):
Time lastRendertime = now();
while(forever)
{
Time current = now();
if ((current - lastRenderTime > 0.04))
{
renderEverything();
lastRenderTime = current;
}
else
{
evolveModelABit();
}
}
Of course, you probably have an input handler to break the loop. Note that this approach assumes that you do not want the model evolution affected by elapsed real time. If you do, and may games do, then pass in the current time to the evolveModelABit();.
For time functions on Windows, you can use:
LARGE_INTEGER frequency; // ticks per second
LARGE_INTEGER t1; // ticks
QueryPerformanceFrequency(&frequency);
QueryPerformanceCounter(&t1);
Note that this approach is suitable for a scientific type simulation. The model evolution will not depend on the frame rate, rendering etc, and gives the same result very time.
For a game, typically there is a push for maximising the fps. This means that the main loop is of the form:
Time lastRendertime = now();
while(forever)
{
Time current = now();
evolveModelABit(current, lastRenderTime);
renderEverything();
lastRenderTime = current;
}
If V-Sync is enabled, SwapBuffers will block the current thread until the next frame has been shown. So if you create a worker thread, and release a lock, or resume its execution right before the call of SwapBuffers your programm recieves the CPU time it would otherwise yield to the rest of the system during the wait-for-swap block. If the worker thread is manipulating GPU resources, it is a good idea using high resolution/performance counters to determine how much time is left until the swap, minus some margin and use this timing in the worker thread, so that the worker thread puts itself to sleep at about the time the swap happens, so that the GPU will not have to context switch between worker and renderer thread.