17

我正在尝试制作一个以恒定帧速率运行的 SDL 程序。但是我发现即使我的程序滞后很多并且跳过了很多帧（即使它以低帧运行并且渲染不多）。

你们有什么建议可以让我的程序运行得更顺畅吗？

#include "SDL.h"
#include "SDL/SDL_ttf.h"

//in milliseconds
const int FPS = 24;
const int SCREENW = 400;
const int SCREENH = 300;
const int BPP = 32;

void apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination) {

    SDL_Rect offset;

    offset.x = x;

    offset.y = y;



    if(SDL_BlitSurface(source, NULL, destination, &offset) < 0) {
        printf("%s\n", SDL_GetError());
    }

}

int main(int argc, char* argv[]) {
    //calculate the period
    double period = 1.0 / (double)FPS;
    period = period * 1000;
    int milliPeriod = (int)period;
    int sleep;

    SDL_Init(SDL_INIT_EVERYTHING);
    TTF_Init();

    TTF_Font* font = TTF_OpenFont("/usr/share/fonts/truetype/freefont/FreeMono.ttf", 24);
    SDL_Color textColor = { 0x00, 0x00, 0x00 };

    SDL_Surface* screen = SDL_SetVideoMode(SCREENW, SCREENH, BPP, SDL_SWSURFACE);
    SDL_Surface* message = NULL;

    Uint32 white = SDL_MapRGB(screen->format, 0xFF, 0xFF, 0xFF);

    SDL_Event event;

    char str[15];

    Uint32 lastTick;
    Uint32 currentTick;
    while(1) {
        while(SDL_PollEvent(&event)) {
            if(event.type == SDL_QUIT) {
                return 0;
            }
            else {
                lastTick = SDL_GetTicks();

                sprintf(str, "%d", lastTick);
                message = TTF_RenderText_Solid(font, str, textColor);
                if(message == NULL) { printf("%s\n", SDL_GetError()); return 1; }

                //the actual blitting
                SDL_FillRect(screen, &screen->clip_rect, white);
                apply_surface(SCREENW / 2, SCREENH / 2, message, screen);

                currentTick = SDL_GetTicks();

                //wait the appropriate amount of time
                sleep = milliPeriod - (currentTick - lastTick);
                if(sleep < 0) { sleep = 0; }
                SDL_Delay(sleep);

                SDL_Flip(screen);
            }
        }
    }

    TTF_CloseFont(font);
    TTF_Quit();
    SDL_Quit();

    return 0;
}
4

3 回答 3

9

在http://www.libsdl.org/release/SDL-1.2.15/docs/html/guidetimeexamples.html有一个如何做到这一点的小例子：

#define TICK_INTERVAL    30

static Uint32 next_time;

Uint32 time_left(void)
{
    Uint32 now;

    now = SDL_GetTicks();
    if(next_time <= now)
        return 0;
    else
        return next_time - now;
}


/* main game loop */

    next_time = SDL_GetTicks() + TICK_INTERVAL;
    while ( game_running ) {
        update_game_state();
        SDL_Delay(time_left());
        next_time += TICK_INTERVAL;
    }
于 2010-03-30T21:08:06.033 回答
8

不要睡觉。

相反，使用线性插值函数来计算每次通过主循环时给定当前时间的位置。这样做将保证无论硬件如何，太空船都会同时到达它们的目的地（尽管在快速的机器上，你会看到更多的中间步骤）。

还有其他插值/混合功能（如线性缓入、缓出、二次缓入/出、三次等）用于其他很酷的效果。

检查此链接： 帧速率独立线性插值

于 2010-03-30T20:48:51.430 回答
3

正如dicroce所说，不要睡觉。为什么？因为大多数桌面操作系统都不是硬实时系统，因此sleep(10)并不意味着“恰好在 10 毫秒内唤醒我”，而是意味着“确保我至少睡 10 毫秒”。这意味着有时您的睡眠时间比您想要的要长得多。这很少是你想要的。如果流畅的游戏玩法很重要，那么通常您只想尽可能频繁地渲染 - SDL_Flip 会为您处理，前提是您的视频驱动程序没有禁用 VSync。

Instead of sleeping, dicroce suggested a linear interpolation algorithm to calculate the correct positions for your entities at any given time. While this is a reasonable strategy for many games, and one I usually use myself, it can cause problems in some cases if not handled carefully: the "Integration Basics" article explains some of this. An alternative offered in the same author's next article, called "Fix Your Timestep".

于 2010-03-31T10:13:00.413 回答