I try to cap the animation at 30 fps. So I design the functions below to achieve the goal. Unfortunately, the animation doesn't behave as fast as no condition checking for setFPSLimit() function when I set 60 fps (DirectX caps game application at 60 fps by default). How should I fix it to make it work?
getGameTime() function counts the time like stopwatch in millisecond when game application starts.
//Called every time you need the current game time
float getGameTime()
{
UINT64 ticks;
float time;
// This is the number of clock ticks since start
if( !QueryPerformanceCounter((LARGE_INTEGER *)&ticks) )
ticks = (UINT64)timeGetTime();
// Divide by frequency to get the time in seconds
time = (float)(__int64)ticks/(float)(__int64)ticksPerSecond;
// Subtract the time at game start to get
// the time since the game started
time -= timeAtGameStart;
return time;
}
With fps limit
http://www.youtube.com/watch?v=i3VDOMqI6ic
void update()
{
if ( setFPSLimit(60) )
updateAnimation();
}
With No fps limit http://www.youtube.com/watch?v=Rg_iKk78ews
void update()
{
updateAnimation();
}
bool setFPSLimit(float fpsLimit)
{
// Convert fps to time
static float timeDelay = 1 / fpsLimit;
// Measure time elapsed
static float timeElapsed = 0;
float currentTime = getGameTime();
static float totalTimeDelay = timeDelay + getGameTime();
if( currentTime > totalTimeDelay)
{
totalTimeDelay = timeDelay + getGameTime();
return true;
}
else
return false;
}
Related
At the moment i have a function that moves my object based on FPS, if the frames have not passed it wont do anything.
It works fine if the computer can run it at that speed.
How would i use time based and move it based on the time?
Here is my code:
typedef unsigned __int64 u64;
auto toolbarGL::Slide() -> void
{
LARGE_INTEGER li = {};
QueryPerformanceFrequency(&li);
u64 freq = static_cast<u64>(li.QuadPart); // clock ticks per second
u64 period = 60; // fps
u64 delay = freq / period; // clock ticks between frame paints
u64 start = 0, now = 0;
QueryPerformanceCounter(&li);
start = static_cast<u64>(li.QuadPart);
while (true)
{
// Waits to be ready to slide
// Keeps looping till stopped then starts to wait again
SlideEvent.wait();
QueryPerformanceCounter(&li);
now = static_cast<u64>(li.QuadPart);
if (now - start >= delay)
{
if (slideDir == SlideFlag::Right)
{
if (this->x < 0)
{
this->x += 5;
this->controller->Paint();
}
else
SlideEvent.stop();
}
else if (slideDir == SlideFlag::Left)
{
if (this->x > -90)
{
this->x -= 5;
this->controller->Paint();
}
else
SlideEvent.stop();
}
else
SlideEvent.stop();
start = now;
}
}
}
You can update your objects by time difference. We need to have start timestamp and then count difference on each iteration of global loop. So global loop is very important too, it has to work all the time. My example shows just call update method for your objects. All your objects should depend on time not FPS. Fps shows different behavior on different computers and even same computer can show different fps because of others processes running in background.
#include <iostream>
#include <chrono>
#include <unistd.h>
//Function to update all objects
void Update( float dt )
{
//For example
//for( auto Object : VectorObjects )
//{
// Object->Update(dt);
//}
}
int main()
{
typedef std::chrono::duration<float> FloatSeconds;
auto OldMs = std::chrono::system_clock::now().time_since_epoch();
const uint32_t SleepMicroseconds = 100;
//Global loop
while (true)
{
auto CurMs = std::chrono::system_clock::now().time_since_epoch();
auto DeltaMs = CurMs - OldMs;
OldMs = CurMs;
//Cast delta time to float seconds
auto DeltaFloat = std::chrono::duration_cast<FloatSeconds>(DeltaMs);
std::cout << "Seconds passed since last update: " << DeltaFloat.count() << " seconds" << std::endl;
//Update all object by time as float value.
Update( DeltaFloat.count() );
// Sleep to give time for system interaction
usleep(SleepMicroseconds);
// Any other actions to calculate can be here
//...
}
return 0;
}
For this example in console you can see something like this:
Seconds passed since last update: 0.002685 seconds
Seconds passed since last update: 0.002711 seconds
Seconds passed since last update: 0.002619 seconds
Seconds passed since last update: 0.00253 seconds
Seconds passed since last update: 0.002509 seconds
Seconds passed since last update: 0.002757 seconds
Your time base logic seems to be incorrect, here's a sample code snippet. The speed of the object should be same irrespective of speed of the system. Instead of QueryPerformanceFrequency which is platform dependent, use std::chrono.
void animate(bool& stop)
{
static float speed = 1080/5; // = 1080px/ 5sec = 5sec to cross screen
static std::chrono::system_clock::time_point start = std::chrono::system_clock::now();
float fps;
int object_x = 1080;
while(!stop)
{
//calculate factional time
auto now = std::chrono::system_clock::now();
auto diff = now - start;
auto lapse_milli = std::chrono::duration_cast<std::chrono::milliseconds>(diff);
auto lapse_sec = lapse_milli.count()/1000;
//apply to object
int incr_x = speed * lapse_sec ;
object_x -= incr_x;
if( object_x <0) object_x = 1080;
// render object here
fps = lapse_milli.count()/1000;
//print fps
std::this_thread::sleep_for(std::chrono::milliseconds(100)); // change to achieve a desired fps rate
start = now;
}
}
I basically need a while loop to only run at 30 "FPS".
I was told to do this:
"Inside your while loop, make a deltaT , and if that deltaT is lesser than 33 miliseconds use sleep(33-deltaT) ."
But I really wasn't quite sure how to initialize the delta/what to set this variable to. I also couldn't get a reply back from the person that suggested this.
I'm also not sure why the value in sleep is 33 instead of 30.
Does anyone know what I can do about this?
This is mainly for a game server to update players at 30FPS, but because I'm not doing any rendering on the server, I need a way to just have the code sleep to limit how many times it can run per second or else it will process the players too fast.
You basically need to do something like this:
int now = GetTimeInMilliseconds();
int lastFrame = GetTimeInMilliseconds();
while(running)
{
now = GetTimeInMilliseconds();
int delta = now - lastFrame;
lastFrame = now;
if(delta < 33)
{
Sleep(33 - delta);
}
//...
Update();
Draw();
}
That way you calculate the amount of milliseconds passed between the current frame and last frame, and if it's smaller than 33 millisecods (1000/30, 1000 milliseconds in a second divided by 30 FPS = 33.333333....) then you sleep until 33 milliseconds has passed. Has for GetTimeInMilliseconds() and Sleep() function, it depends on the library that you're using and/or the platform.
c++11 provides a simple mechanism for that:
#include <chrono>
#include <thread>
#include <iostream>
using namespace std;
using namespace std::chrono;
void doStuff(){
std::cout << "Loop executed" << std::endl;
}
int main() {
time_point<system_clock> t = system_clock::now();
while (1) {
doStuff();
t += milliseconds(33);
this_thread::sleep_until(t);
}
}
The only thing you have to be aware of though is that if one loop iteration takes longer than the 33ms, the next two iterations will be executed without a pause in between (until t has caught up with the real time), which may or may not be what you want.
Glenn Fiedler has written a nice article on this topic a few years ago. Hacking with sleep() is not very precise, instead you want to run your physics a fixed number of times per second, let your graphics run freely, and between frames, you do as many fixed timesteps as time has passed.
The code that follows looks intimidating at first, but once you get the idea, it becomes simple; it's best to read the article completely.
Fix Your Timestep
double t = 0.0;
double dt = 0.01;
double currentTime = hires_time_in_seconds();
double accumulator = 0.0;
State previous;
State current;
while ( !quit )
{
double newTime = hires_time_in_seconds();
double frameTime = newTime - currentTime;
if ( frameTime > 0.25 )
frameTime = 0.25;
currentTime = newTime;
accumulator += frameTime;
while ( accumulator >= dt )
{
previousState = currentState;
integrate( currentState, t, dt );
t += dt;
accumulator -= dt;
}
const double alpha = accumulator / dt;
State state = currentState * alpha +
previousState * ( 1.0 - alpha );
render( state );
}
If it goes offline, there should be several backups available; however, I remember Gaffer on Games for many years already.
I'm trying to calculate the framerate of a GLUT window by calling a custom CalculateFrameRate method I made at the beginning of my Display() callback function. I call glutPostRedisplay() after calculations I perform every frame so Display() gets called for every frame.
I also have an int numFrames that increments every frame (every time glutPostRedisplay gets called) and I print that out as well. My CalculateFrameRate method calculates a rate of about 7 fps but if I look at a stopwatch and compare it to how quickly my numFrames incrementor increases, the framerate is easily 25-30 fps.
I can't seem to figure out why there is such a discrepancy. I've posted my CalcuateFrameRate method below
clock_t lastTime;
int numFrames;
//GLUT Setup callback
void Renderer::Setup()
{
numFrames = 0;
lastTime = clock();
}
//Called in Display() callback every time I call glutPostRedisplay()
void CalculateFrameRate()
{
clock_t currentTime = clock();
double diff = currentTime - lastTime;
double seconds = diff / CLOCKS_PER_SEC;
double frameRate = 1.0 / seconds;
std::cout<<"FRAMERATE: "<<frameRate<<endl;
numFrames ++;
std::cout<<"NUM FRAMES: "<<numFrames<<endl;
lastTime = currentTime;
}
The function clock (except in Windows) gives you the CPU-time uses, so if you are not spinning the CPU for the entire frame-time, then it will give you a lower time than expected. Conversely, if you have 16 cores running 16 of your threads flat out, the time reported by clock will be 16 times the actual time.
You can use std::chrono::steady_clock, std::chrono::high_resolution_clock, or if you are using Linux/Unix, gettimeofday (which gives you microosecond resolution).
Here's a couple of snippets of how to use gettimeofday to measure milliseconds:
double time_to_double(timeval *t)
{
return (t->tv_sec + (t->tv_usec/1000000.0)) * 1000.0;
}
double time_diff(timeval *t1, timeval *t2)
{
return time_to_double(t2) - time_to_double(t1);
}
gettimeofday(&t1, NULL);
... do stuff ...
gettimeofday(&t2, NULL);
cout << "Time taken: " << time_diff(&t1, &t2) << "ms" << endl;
Here's a piece of code to show how to use std::chrono::high_resolution_clock:
auto start = std::chrono::high_resolution_clock::now();
... stuff goes here ...
auto diff = std::chrono::high_resolution_clock::now() - start;
auto t1 = std::chrono::duration_cast<std::chrono::nanoseconds>(diff);
After doing some research and debugging in my C++ project with glfwGetTime(), I'm having trouble making a game loop for my project. As far as time goes I really only worked with nanoseconds in Java and on the GLFW website it states that the function returns the time in seconds. How would I make a fixed time step loop with glfwGetTime()?
What I have now -
while(!glfwWindowShouldClose(window))
{
double now = glfwGetTime();
double delta = now - lastTime;
lastTime = now;
accumulator += delta;
while(accumulator >= OPTIMAL_TIME) // OPTIMAL_TIME = 1 / 60
{
//tick
accumulator -= OPTIMAL_TIME;
}
}
All you need is this code for limiting updates, but keeping the rendering at highest possible frames. The code is based on this tutorial which explains it very well. All I did was to implement the same principle with GLFW and C++.
static double limitFPS = 1.0 / 60.0;
double lastTime = glfwGetTime(), timer = lastTime;
double deltaTime = 0, nowTime = 0;
int frames = 0 , updates = 0;
// - While window is alive
while (!window.closed()) {
// - Measure time
nowTime = glfwGetTime();
deltaTime += (nowTime - lastTime) / limitFPS;
lastTime = nowTime;
// - Only update at 60 frames / s
while (deltaTime >= 1.0){
update(); // - Update function
updates++;
deltaTime--;
}
// - Render at maximum possible frames
render(); // - Render function
frames++;
// - Reset after one second
if (glfwGetTime() - timer > 1.0) {
timer ++;
std::cout << "FPS: " << frames << " Updates:" << updates << std::endl;
updates = 0, frames = 0;
}
}
You should have a function update() for updating game logic and a render() for rendering. Hope this helps.
I am making a small game with C++ OpenGL. update() is normally called once every time the program runs through the code. I am trying to limit this to 60 times per second (I want the game to update at the same speed on different speed computers).
The code included below runs a timer and should call update() once the timer is >= than 0.0166666666666667 (60 times per second). However the statement if((seconds - lastTime) >= 0.0166666666666667) seems only to be tripped once per second. Does anyone know why?
Thanks in advance for your help.
//Global Timer variables
double secondsS;
double lastTime;
time_t timer;
struct tm y2k;
double seconds;
void init()
{
glClearColor(0,0,0,0.0); // Sets the clear colour to white.
// glClear(GL_COLOR_BUFFER_BIT) in the display function
//Init viewport
viewportX = 0;
viewportY = 0;
initShips();
//Time
lastTime = 0;
time_t timerS;
struct tm y2k;
y2k.tm_hour = 0; y2k.tm_min = 0; y2k.tm_sec = 0;
y2k.tm_year = 100; y2k.tm_mon = 0; y2k.tm_mday = 1;
time(&timerS); /* get current time; same as: timer = time(NULL) */
secondsS = difftime(timerS,mktime(&y2k));
printf ("%.f seconds since January 1, 2000 in the current timezone \n", secondsS);
loadTextures();
ShowCursor(true);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
}
void timeKeeper()
{
y2k.tm_hour = 0; y2k.tm_min = 0; y2k.tm_sec = 0;
y2k.tm_year = 100; y2k.tm_mon = 0; y2k.tm_mday = 1;
time(&timer); /* get current time; same as: timer = time(NULL) */
seconds = difftime(timer,mktime(&y2k));
seconds -= secondsS;
//Run 60 times a second. This limits updates to a constant standard.
if((seconds - lastTime) >= 0.0166666666666667)
{
lastTime = seconds;
update();
//printf ("%.f seconds since beginning program \n", seconds);
}
}
timeKeeper() is called in int WINAPI WinMain, while the program is !done
EDIT:
Thanks to those who helped, you pointed me on the right track. As mentioned in the answer below <ctime> does not have ms accuracy. I have therefore implemented the following code that has the correct accuracy:
double GetSystemTimeSample()
{
FILETIME ft1, ft2;
// assume little endian and that ULONGLONG has same alignment as FILETIME
ULONGLONG &t1 = *reinterpret_cast<ULONGLONG*>(&ft1),
&t2 = *reinterpret_cast<ULONGLONG*>(&ft2);
GetSystemTimeAsFileTime(&ft1);
do
{
GetSystemTimeAsFileTime(&ft2);
} while (t1 == t2);
return (t2 - t1) / 10000.0;
}//GetSystemTimeSample
void timeKeeper()
{
thisTime += GetSystemTimeSample();
cout << thisTime << endl;
//Run 60 times a second. This limits updates to a constant standard.
if(thisTime >= 16.666666666666699825) //Compare to a value in milliseconds
{
thisTime = seconds;
update();
}
}
http://www.cplusplus.com/reference/ctime/difftime/
Calculates the difference in seconds between beginning and end
So, you get a value in seconds. So, even if your value is double, you will get an integer.
So, you only get a difference between a value and the previous one when that difference is at least of 1 second.