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所以我正在开发打砖块，而运动对我来说滞后。
我不知道它为什么滞后，因为我听说 60 fps 是眼罩。
关于我应该做什么的任何建议，因为我不想以 100 fps 编程游戏，
因为如果我可以以 60 fps 编程它们，我有更少的时间来处理我的计算？
这是我的封顶框架代码。 

//Cap the frame rate                
if( fps.get_ticks() < 1000 / FRAMES_PER_SECOND )   
{   
    SDL_Delay( ( 1000 / FRAMES_PER_SECOND ) - fps.get_ticks() );   
}

如果您好奇，这是我的全部代码 

/*This source code copyrighted by Lazy Foo' Productions (2004-2012)
and may not be redistributed without written permission.*/

//The headers
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include <string>

//The screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The frame rate
const int FRAMES_PER_SECOND = 40;

//The dimensions of the dot
const int DOT_WIDTH = 20;
const int DOT_HEIGHT = 20;

//The surfaces
SDL_Surface *dot = NULL;
SDL_Surface *screen = NULL;

//The event structure
SDL_Event event;

//The dot that will move around on the screen
class Dot
{
    private:
    //The X and Y offsets of the dot
    int x, y;

    //The velocity of the dot
    int xVel, yVel;

    public:
    //Initializes the variables
    Dot();

    //Takes key presses and adjusts the dot's velocity
    void handle_input();

    //Moves the dot
    void move();

    //Shows the dot on the screen
    void show();
};

//The timer
class Timer
{
    private:
    //The clock time when the timer started
    int startTicks;

    //The ticks stored when the timer was paused
    int pausedTicks;

    //The timer status
    bool paused;
    bool started;

    public:
    //Initializes variables
    Timer();

    //The various clock actions
    void start();
    void stop();
    void pause();
    void unpause();

    //Gets the timer's time
    int get_ticks();

    //Checks the status of the timer
    bool is_started();
    bool is_paused();
};

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;

    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;

    //Load the image
    loadedImage = IMG_Load( filename.c_str() );

    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );

        //Free the old surface
        SDL_FreeSurface( loadedImage );

        //If the surface was optimized
        if( optimizedImage != NULL )
        {
            //Color key surface
            SDL_SetColorKey( optimizedImage, SDL_SRCCOLORKEY, SDL_MapRGB(     optimizedImage->format, 0, 0xFF, 0xFF ) );
        }
    }

    //Return the optimized surface
    return optimizedImage;
}

void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination,                 SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;

    //Get offsets
    offset.x = x;
    offset.y = y;

    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE         );

    //If there was an error in setting up the screen
    if( screen == NULL )
    {
        return false;
    }

    //Set the window caption
    SDL_WM_SetCaption( "Move the Dot", NULL );

    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the dot image
    dot = load_image( "dot.bmp" );

    //If there was a problem in loading the dot
    if( dot == NULL )
    {
       return false;
    }

    //If everything loaded fine
    return true;
}

void clean_up()
{
    //Free the surface
    SDL_FreeSurface( dot );

    //Quit SDL
    SDL_Quit();
}

Dot::Dot()
{
    //Initialize the offsets
    x = 0;
    y = 0;

    //Initialize the velocity
    xVel = 0;
    yVel = 0;
}

void Dot::handle_input()
{
    //If a key was pressed
    if( event.type == SDL_KEYDOWN )
    {
        //Adjust the velocity
        switch( event.key.keysym.sym )
        {
            case SDLK_UP: yVel -= DOT_HEIGHT / 2; break;
            case SDLK_DOWN: yVel += DOT_HEIGHT / 2; break;
            case SDLK_LEFT: xVel -= DOT_WIDTH / 2; break;
            case SDLK_RIGHT: xVel += DOT_WIDTH / 2; break;
        }
    }
    //If a key was released
    else if( event.type == SDL_KEYUP )
    {
        //Adjust the velocity
        switch( event.key.keysym.sym )
        {
            case SDLK_UP: yVel += DOT_HEIGHT / 2; break;
           case SDLK_DOWN: yVel -= DOT_HEIGHT / 2; break;
            case SDLK_LEFT: xVel += DOT_WIDTH / 2; break;
            case SDLK_RIGHT: xVel -= DOT_WIDTH / 2; break;
        }
    }
}

void Dot::move()
{
    //Move the dot left or right
    x += xVel;

    //If the dot went too far to the left or right
    if( ( x < 0 ) || ( x + DOT_WIDTH > SCREEN_WIDTH ) )
    {
        //move back
        x -= xVel;
    }

    //Move the dot up or down
    y += yVel;

    //If the dot went too far up or down
    if( ( y < 0 ) || ( y + DOT_HEIGHT > SCREEN_HEIGHT ) )
    {
        //move back
        y -= yVel;
    }
}

void Dot::show()
{
    //Show the dot
    apply_surface( x, y, dot, screen );
}

Timer::Timer()
{
    //Initialize the variables
    startTicks = 0;
    pausedTicks = 0;
    paused = false;
    started = false;
}

void Timer::start()
{
    //Start the timer
    started = true;

    //Unpause the timer
    paused = false;

    //Get the current clock time
    startTicks = SDL_GetTicks();
}

void Timer::stop()
{
    //Stop the timer
    started = false;

    //Unpause the timer
    paused = false;
}

void Timer::pause()
{
    //If the timer is running and isn't already paused
    if( ( started == true ) && ( paused == false ) )
    {
        //Pause the timer
        paused = true;

        //Calculate the paused ticks
        pausedTicks = SDL_GetTicks() - startTicks;
    }
}

void Timer::unpause()
{
    //If the timer is paused
    if( paused == true )
    {
        //Unpause the timer
        paused = false;

        //Reset the starting ticks
        startTicks = SDL_GetTicks() - pausedTicks;

        //Reset the paused ticks
        pausedTicks = 0;
    }
}

int Timer::get_ticks()
{
    //If the timer is running
    if( started == true )
    {
        //If the timer is paused
        if( paused == true )
        {
            //Return the number of ticks when the timer was paused
            return pausedTicks;
        }
        else
        {
            //Return the current time minus the start time
            return SDL_GetTicks() - startTicks;
        }
    }

   //If the timer isn't running
    return 0;
}

bool Timer::is_started()
{
    return started;
}

bool Timer::is_paused()
{
    return paused;
}

int main( int argc, char* args[] )
{
    //Quit flag
   bool quit = false;

    //The dot that will be used
    Dot myDot;

    //The frame rate regulator
    Timer fps;

    //Initialize
    if( init() == false )
    {
        return 1;
    }    

    //Load the files
    if( load_files() == false )
    {
        return 1;
    }

    //While the user hasn't quit
    while( quit == false )
    {
        //Start the frame timer
       fps.start();

       //While there's events to handle
        while( SDL_PollEvent( &event ) )
        {
            //Handle events for the dot
            myDot.handle_input();

            //If the user has Xed out the window
            if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
        }

        //Move the dot
        myDot.move();

        //Fill the screen white
        SDL_FillRect( screen, &screen->clip_rect, SDL_MapRGB( screen->format, 0xFF, 0xFF, 0xFF ) );

        //Show the dot on the screen
        myDot.show();

        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
           return 1;
        }

        //Cap the frame rate
        if( fps.get_ticks() < 1000 / FRAMES_PER_SECOND )
        {
            SDL_Delay( ( 1000 / FRAMES_PER_SECOND ) - fps.get_ticks() );
        }
    }

    //Clean up
    clean_up();

    return 0;
}
4

1 回答 1

2

由于舍入，您正在失去微秒（可能是毫秒），这会导致奇怪的行为。IE。您的逻辑不会以恒定的速度运行。

您可以做的类似于以下内容（考虑它是伪代码，因为我对 SDL 有点过时了）：

unsigned int lag = 0;

while (running) { // main loop
    // do event handling here
    lag += passed_time;
    reset_timer();

    // This loop is a bit more complicated:
    // - Do up to 'max_runs' logic steps
    // - Do this while the remaining time that passed since last frame is bigger than the time for one frame ('frame_time')
    // - Every loop, increase the number of runs done by 1 and sub the time for one frame
    // - For a 100 Hz simulation (100 logic steps per second), 'frame_time' would be 10.
    // - For a 60 Hz simulation (60 logic steps per second), 'frame_time' would be 17.
    for (int runs = 0; runs < max_runs && lag > frame_time; ++runs, lag -= frame_time) {
        // do game logic here
    }
    // Drop additional logic steps we couldn't process
    lag = lag % frame_time;

    // do render stuff here

    sleep(1); // Sleep for 1 millisecond to avoid having a 'passed_time' of 0 on very fast systems (depends on your timer resolution)
}

您的计时器分辨率越高，您的游戏运行就越流畅。尽管这种逻辑应该将“滞后”保持在最低限度。通过这种方式使用计时，您还可以节省“等待”以获得特定帧速率。您仍然可以限制它，但您也可以只启用 VSync，这将是更好的方法。

编辑：这段代码实际上做的很简单：

  • 首先，它将自上次迭代以来经过的时间与我们在上次迭代中忽略的时间相加。
  • 这为您提供了自上一个逻辑步骤以来的时间窗口（逻辑步骤可以是与游戏逻辑相关的任何内容，例如移动玩家、移动子弹、添加或移除对象等）。
  • 在此时间范围内每（例如）10 毫秒，运行一次逻辑步骤。如果 50 毫秒过去了，您运行游戏逻辑 5 次以赶上。如果不到 10 毫秒，你什么都不做。
  • 为了避免锁定无法赶上的较慢计算机（无法处理每秒给定的迭代次数），有一个最大迭代次数要赶上。几行之后的模运算符 (%) 删除了被丢弃的开销。
  • 为了避免计算机太快什么都不做（由于四舍五入从来没有时间相加），整个循环等待 1 毫秒，所以总是至少有 1 毫秒要添加。

要获得经过的时间（以毫秒为单位）：

unsigned int timestamp = SDL_GetTicks(); // on startup or right before entering your main loop

// when you need the time passed:
unsigned int time_now = SDL_GetTicks(); // get current time
unsigned int time_passed = time_now - timestamp; // get time difference/time passed
timestamp = time_now; // essentially reset the timer

这样你可能仍然会损失一些微秒，但你应该没问题（比等待更好）。

编辑：我还没有看过新的 SDL，所以你可能不得不使用一些方法而不是 C 风格的函数。只需查看文档即可。

这是一个不需要任何其他库的示例（仅适用于 Windows，不确定您正在使用哪个系统）。请记住，这只是我整理的一些快速代码（也可以使用 MinGW、MSVC 编译良好）。

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <cstdio>

__int64 frequency = 0;
__int64 last_time = 0;

double lag = 0;
double stat_lag = 0;

unsigned int render_steps = 0;
unsigned int logic_steps = 0;

const unsigned char target_updates_per_second = 100;
const unsigned char target_frames_per_second = 60;

// reset or initialize the timer
void reset_timer(__int64 *timer) {
    QueryPerformanceFrequency((PLARGE_INTEGER)&frequency);
    QueryPerformanceCounter((PLARGE_INTEGER)timer);
}

// get the time since last query and reset the timer for next iteration
double get_delta(__int64 *timer) {
    __int64 temp; // stores the new timestamp
    __int64 delta; // stores the difference
    QueryPerformanceCounter((PLARGE_INTEGER)&temp);
    delta = temp - *timer;
    *timer = temp;
    return (double)delta / frequency;
}

int main(int argc, char *argv[]) {
    reset_timer(&last_time);

    const unsigned int logic_frame_time = 1000 / target_updates_per_second;
    const unsigned int render_frame_time = 1000 / target_frames_per_second;

    while (1) {
        double delta = 1000 * get_delta(&last_time); // get the time that passed since last iteration (multiplied with 1000 for milliseconds)

        lag += delta; // here we add the time passed to the lag counter/timer
        stat_lag += delta; // here we do the same for the fps/ups counter

        for (char runs = 0; runs < 10 && lag > logic_frame_time; ++runs, lag -= logic_frame_time) {
            ++logic_steps; // here game logic would happen

            Sleep(0); // increase this number to simulate more load during logic steps
        }

        // lag = lag % logic_frame_time;
        // i made it the manual way to keep the double value, which is more precise here
        while (lag > logic_frame_time)
            lag -= logic_frame_time;

        if (stat_lag > 1000) { // if more than 1 second passed
            printf("updates per second: %u\nframes per second: %u\n\n", logic_steps, render_steps);

            // reset the stats
            logic_steps = 0;
            render_steps = 0;

            // stat_lag = stat_lag % 1000;
            // as above, doing it the manual way for double
            while (stat_lag > 1000)
                stat_lag -= 1000;
        }

        ++render_steps; // here rendering would happen

        // here, vsync would slow down processing, lowering the number of frames per second!
        //Sleep(...);

        Sleep(1); // avoid 0 milliseconds passing; this also causes rendering to be limited to 1000 fps!
    }
}
于 2012-09-18T11:06:19.913 回答