在SDL中管理輸入？

Question

我使用SDL在C++中創建pong克隆。槳準備就緒並根據用戶輸入進行移動。令我擔心的是輸入信號很奇怪，我預計兩個槳的平穩移動，但是當另一個槳移動時，一個槳會滯後，另一個槳不移動時會加速。我懷疑這是不是由於封鎖FPS或者我設法獲得多個輸入或者兩者兼而有之的奇怪方式造成的。任何人都可以告訴我我的代碼中出現了什麼問題，以及如何改進它？

我的代碼：

#include <SDL/SDL.h> 
#include <string> 
#include "SDL/SDL_image.h" 
#include <SDL/SDL_ttf.h> 

bool quit = false; 
bool keyheld[323]={false}; 
const int SCREEN_WIDTH = 800; 
const int SCREEN_HEIGHT = 600; 
const int SCREEN_BPP = 32; 
int paddle1x = 0; 
int paddle1y = 50; 
int paddle2x = 600; 
int paddle2y = 500; 

SDL_Color color = {255,255,255}; 
SDL_Event event; 
SDL_Surface* screen = NULL; 
SDL_Surface* timer = NULL; 
SDL_Surface* background = NULL; 
SDL_Surface* paddle1 =NULL; 
SDL_Surface* paddle2 = NULL; 

void apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination) 
{ 
    SDL_Rect offset; 
    offset.x = x; 
    offset.y = y; 
    SDL_BlitSurface(source, NULL,destination, &offset); 
} 

SDL_Surface *load_image(std::string filename) 
    { 
     SDL_Surface* loadedimage = NULL; 
     SDL_Surface* optimisedimage = NULL; 

     loadedimage= IMG_Load(filename.c_str()); 
     optimisedimage= SDL_DisplayFormatAlpha(loadedimage); 
     SDL_FreeSurface(loadedimage); 

     return optimisedimage; 
    } 

int main(int argc, char *args[]) 
{ 
    bool quit = false; 
    bool keyheld[323]={false}; 
    int p1score=0; 
    int p2score=0; 

    SDL_Init(SDL_INIT_EVERYTHING); 
    TTF_Init(); 
    TTF_Font *font=NULL; 

    screen = SDL_SetVideoMode(SCREEN_WIDTH,SCREEN_HEIGHT,SCREEN_BPP,SDL_SWSURFACE); 

    background = load_image("background.png"); 
    apply_surface(0,0,background,screen); 

    paddle1 = load_image("paddle1.png"); 
    apply_surface(paddle1x,paddle1y,paddle1,screen); 

    paddle2=load_image("paddle2.png"); 
    apply_surface(paddle2x,paddle2y,paddle2,screen); 


    font = TTF_OpenFont("kremlin.ttf", 22); 

    timer = TTF_RenderText_Solid(font,"Test!",color); 
    apply_surface(0,0,timer,screen); 

    SDL_WM_SetCaption("PONG!",NULL); 
    SDL_Flip(screen); 
    while(quit==false) 
    { 
      if(SDL_PollEvent(&event)) 
      { 
       SDLKey keyPressed = event.key.keysym.sym; 
       if(event.type==SDL_QUIT) 
       { 
        return 0; 
       } 
       else if(event.type==SDL_KEYDOWN) 
       { 
        keyheld[keyPressed] = true; 
       } 
       else if(event.type==SDL_KEYUP) 
       { 
        keyheld[keyPressed] = false; 
       } 



      } 
      if(keyheld[SDLK_LEFT]) 
      { 
       paddle1x--; 
       apply_surface(0,0,background,screen); 
       apply_surface(paddle1x,paddle1y,paddle1,screen); 
       apply_surface(paddle2x,paddle2y,paddle2,screen); 
      } 
      if(keyheld[SDLK_RIGHT]) 
      { 
       paddle1x++; 
       apply_surface(0,0,background,screen); 
       apply_surface(paddle1x,paddle1y,paddle1,screen); 
       apply_surface(paddle2x,paddle2y,paddle2,screen); 
      } 
      if(keyheld[SDLK_a]) 
       { 
       paddle2x--; 
       apply_surface(0,0,background,screen); 
       apply_surface(paddle1x,paddle1y,paddle1,screen); 
       apply_surface(paddle2x,paddle2y,paddle2,screen); 
       } 
       if(keyheld[SDLK_d]) 
       { 
       paddle2x++; 
       apply_surface(0,0,background,screen); 
       apply_surface(paddle1x,paddle1y,paddle1,screen); 
       apply_surface(paddle2x,paddle2y,paddle2,screen); 
       } 

      apply_surface(0,0,timer,screen); 
      SDL_Flip(screen); 
      SDL_Delay(2); 
    } 

    return 0; 
} 

Answer 1

的問題是，因爲你更新每一個類型的槳移動的後備緩衝。如果兩個槳移動，最終會更新兩次。這是你遇到放緩的地方。您應該每幀更新一次緩衝器。像這樣：

if(keyheld[SDLK_LEFT]) 
{ 
    paddle1x--; 
} 
if(keyheld[SDLK_RIGHT]) 
{ 
    paddle1x++; 
} 
if(keyheld[SDLK_a]) 
{ 
    paddle2x--; 
} 
if(keyheld[SDLK_d]) 
{ 
    paddle2x++; 
} 

// Now we do the update. You can always add a flag to see if the update 
// really needs to be done and skip it if it doesn't 
apply_surface(0,0,background,screen); 
apply_surface(paddle1x,paddle1y,paddle1,screen); 
apply_surface(paddle2x,paddle2y,paddle2,screen); 

apply_surface(0,0,timer,screen); 
SDL_Flip(screen); 
SDL_Delay(2);