SDL_GetTicks () accuracy below millisecond level
I am currently programming something with SDL2. Everything works fine, but I have a problem with the method SDL_GetTicks()
. It should normally return the total application time in milliseconds, but it always returns most of the time 0, and sometimes 1.
I have initialized SDL with a flag SDL_INIT_EVERYTHING
.
The problem with the following code is that the loop is too fast, so the delta time is less than 1ms. Is there a way to achieve higher precision?
#include "Application.hpp"
void Application::Initialize()
{
int sdl_initialize_result = SDL_Init(SDL_INIT_EVERYTHING);
if(sdl_initialize_result < 0)
{
std::cerr << "Failed to initialize SDL !" << std::endl << SDL_GetError() << std::endl;
}
window = SDL_CreateWindow("Project Unknown", 100, 100, 800, 600, SDL_WINDOW_SHOWN);
if(window == nullptr)
{
std::cerr << "Failed to create SDL window !" << std::endl << SDL_GetError() << std::endl;
}
last_update_time = SDL_GetTicks();
}
void Application::Dispose()
{
SDL_DestroyWindow(window);
SDL_Quit();
}
void Application::Render()
{
}
void Application::Update()
{
Uint32 current_time = SDL_GetTicks();
Uint32 delta_time = current_time - last_update_time;
SDL_Event event;
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_QUIT:
{
should_close = true;
}
break;
default:
{
}
break;
}
}
// Update game objects with delta_time
last_update_time = current_time;
}
void Application::Run()
{
Initialize();
should_close = false;
do
{
Render();
Update();
}
while(should_close == false);
Dispose();
}
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You cannot use SDL_GetTicks () if you want higher precision, but there are many other alternatives. If you want to be platform independent you need to be careful, but here is a portable C ++ 11 example to get you started:
#include <iostream>
#include <chrono>
typedef std::chrono::high_resolution_clock Clock;
int main()
{
auto t1 = Clock::now();
auto t2 = Clock::now();
std::cout << "Delta t2-t1: "
<< std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1).count()
<< " nanoseconds" << std::endl;
}
Running this on ideone.com gave me:
Delta t2-t1: 282 nanoseconds
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Well of course you need to actually wait until> = 1ms has passed before updating your last checkbox counter
void Application::Update()
{
Uint32 current_time = SDL_GetTicks();
Uint32 delta_time = current_time - last_update_time;
SDL_Event event;
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_QUIT:
{
should_close = true;
}
break;
default:
break;
}
}
if (delta_time >= 1)
{
// Update game objects with delta_time
last_update_time = current_time;
}
}
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