最近我一直在研究一些SDL包装以供我自己使用,而且自从我首次开始使用SDL库以来,我遇到了一直存在的问题。C++ SDL帧速率脉冲
看到,像许多其他人一样,我一直在使用一个类似于这个http://lazyfoo.net/SDL_tutorials/lesson14/index.php的计时器来调节我的帧率,并且运动永远不会平滑。它似乎不是一个双缓冲或vsync问题,而是运动平稳但周期性地跳过和断断续续(实际上它有一定的脉冲和节奏)。无论何时只要调整帧率,脉冲消失 - 当然,一切都变得无法使用),所以我确信它必须处理它。
我已经把一个只包含计时器和一个红色正方形的小应用程序组合在一起。我将把代码放在这篇文章的末尾。代码是垃圾,不会使用任何类型的精灵或任何东西:只要知道它无论施加多少压力(比如说,添加更多移动的东西或仅更新屏幕的一部分)就可以结束。我尝试过不同的帧速率设置,并且脉冲总是出现(只是具有不同的“速度”)。不用说我已经在几台机器(linux机器上,都是这样)上试过了。
无论如何,我一直在阅读和看到其他人有这个问题,但没有真正的答案。其中之一就是关于三角洲计时技术,并乐意尝试,但我的问题在于计时器本身就是这个非常简单的应用程序。它为什么口吃? SDL_GetTicks的精度和准确性有问题吗?我能做些什么来改善它?
所以,这里是为那些谁想要尝试它的代码:
#include <SDL/SDL.h>
class fps_control
{
private:
bool apply;
Uint32 ticks_frame_count;
Uint32 ticks_frame_end;
Uint32 ticks_frame_begin;
Uint32 diff;
unsigned int frame_count; //Visible to the outside
unsigned int frame_count_inner; //Keeps count until a second has passed, then overwrites former to give the elapsed frames in a second.
unsigned int frame_length;
unsigned int desired_framerate;
private:
void calculate_frame_length()
{
this->frame_length=1000/this->desired_framerate;
}
public:
fps_control(unsigned int p_f=30):desired_framerate(p_f), apply(true), ticks_frame_count(0), ticks_frame_end(0), ticks_frame_begin(0), diff(0), frame_count(0), frame_count_inner(0), frame_length(0)
{
this->calculate_frame_length();
}
unsigned int get_frame_count() const {return this->frame_count;}
unsigned int get_desired_framerate() const {return this->desired_framerate;}
void framerate_increase(){this->set_framerate(this->desired_framerate+1);}
void framerate_decrease(){this->set_framerate(this->desired_framerate+1);}
void set_framerate(unsigned int p_param)
{
this->desired_framerate=p_param;
this->calculate_frame_length();
}
void toggle_apply() {this->apply=!this->apply;}
void init()
{
//Call this once before starting, to set the beginning frame count to the initial values.
this->ticks_frame_count=SDL_GetTicks();
this->ticks_frame_begin=this->ticks_frame_count;
this->frame_count_inner=0;
this->frame_count=0;
}
void turn()
{
//Call this when all drawing and logic is done.
if(!this->apply) return; //Only apply when asked for.
//Ask for time before drawing and logic to calculate the difference. Add a frame.
this->ticks_frame_end=SDL_GetTicks();
this->frame_count_inner++;
//Whenever a second has passed, update the visible frame count.
if((this->ticks_frame_end - this->ticks_frame_count) > 1000)
{
this->frame_count=this->frame_count_inner;
this->frame_count_inner=0;
this->ticks_frame_count=SDL_GetTicks();
}
//Calculate difference and apply delay when needed.
this->diff=this->ticks_frame_end - this->ticks_frame_begin;
if(this->diff < this->frame_length) SDL_Delay(this->frame_length-this->diff);
//Get the beginning time and start again.
this->ticks_frame_begin=SDL_GetTicks();
}
};
class Box
{
private:
SDL_Rect position;
int movement_x;
int movement_y;
public:
Box():movement_x(4), movement_y(4)
{
this->position.x=100;
this->position.y=100;
this->position.w=30;
this->position.h=30;
}
SDL_Rect get_position() {return this->position;}
void move_around()
{
//Won't touch the edges, but doesn't really matter.
if(this->position.x<=0 || this->position.x>=800-this->position.w) this->movement_x=-this->movement_x;
if(this->position.y<=0 || this->position.y>=600-this->position.h) this->movement_y=-this->movement_y;
this->position.x+=this->movement_x;
this->position.y+=this->movement_y;
}
};
bool init_sdl(){return SDL_Init(SDL_INIT_VIDEO) >= 0;}
void quit_sdl(){SDL_Quit();}
void fill_screen(SDL_Surface * screen)
{
SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format,0,0,0));
}
void update_screen(SDL_Surface * screen, Box& box)
{
SDL_Rect b=box.get_position();
SDL_FillRect(screen, &b, SDL_MapRGB(screen->format, 200, 20, 20));
SDL_Flip(screen);
}
int get_input()
{
SDL_Event event;
while(SDL_PollEvent(&event))
{
if(event.type==SDL_QUIT) return 1;
else if(event.type==SDL_KEYDOWN)
{
switch(event.key.keysym.sym)
{
case SDLK_ESCAPE: return 1; break;
case SDLK_SPACE: return 2; break;
case SDLK_UP: return 3; break;
case SDLK_DOWN: return 4; break;
default: break;
}
}
}
return 0;
}
int main(int argc, char **argv)
{
if(!init_sdl())
{
return 1;
}
else
{
//Init things...
// SDL_Surface * screen=SDL_SetVideoMode(800, 600, 16, SDL_DOUBLEBUF | SDL_HWSURFACE); /*SDL_SWSURFACE | SDL_ANYFORMAT);*/
SDL_Surface * screen=SDL_SetVideoMode(800, 600, 16, SDL_SWSURFACE | SDL_ANYFORMAT);
Box box=Box();
fps_control fps=fps_control(60); //Framerate is set to 60.
bool run=true;
int input=0;
SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format,255,0,0));
//Main loop
fps.init();
while(run)
{
input=get_input();
switch(input)
{
case 1: run=false; break;
case 2: fps.toggle_apply(); break;
case 3: fps.framerate_increase(); break;
case 4: fps.framerate_decrease(); break;
default: break;
}
box.move_around();
fill_screen(screen);
update_screen(screen, box);
fps.turn();
}
quit_sdl();
}
}
它是自包含的(并再次,纯垃圾),所以正好与SDL链接,并尝试...你在这里看到任何口吃脉冲?
我会尝试应用增量计时以查看问题是否消失。我只是想知道为什么会发生这种简单的应用程序。非常感谢。
编辑:最后一件事,我知道我可能不应该去SDL_Delay(关于系统睡至少问值),但我真的很困惑这种看似强大的机器上的行为。
编辑:修正了一下“set_framerate”,感谢Yno对它的评论。
编辑2:因为我改变了所有的代码,使用增量时间值而不是设置帧率,所有的东西都变得更好了。我仍然得到一些周期性的减速(这次每次四十秒),但我可以责怪那些在系统上,因为根据我使用的Linux桌面(比如Gnome,Unity,Gnome2d ...),帧率和减速变化很大。
感谢您的回答......其实,帧率降低为错误的,因为它得到(有些错字我有没有),但calculate_frame_length()在构造函数中,对吗?该代码实际上是西班牙文原件的翻译,因此可能会有一些不一致之处。至于其他方面,我会说这是全部,只有其他形式,对吧? [继续,打破“输入键”] –
即使有些东西可能是越野车或奇怪的(比如第一个t(ticks_frame_begin是在最后计算的),我不认为我应该期待这个脉冲.. 。除非SDL_Delay有什么错误,当然,一切都会有帮助,非常感谢:)。 –
'calculate_frame_length()'应当每当所需的帧率发生变化时调用,即在'set_framerate()'中。我将编辑我的帖子。 – Yno