無法使用SDL將字符移動到正確的位置？

Question

我目前有問題移動一個字符權利，並顯示他像他正在運行，但是當我按下右鍵後，它向右移動一次，然後當我進入左側它再次離開，但再次按右鍵不會去再對。這裏是我的代碼，我使用：

#include <SDL2/SDL.h> 

#include "game.h" 
#include "graphics.h" 
#include "input.h" 

/* Game class 
* This class holds all information for our game loop 
*/ 

namespace { 
    const int FPS = 50; 
    const int MAX_FRAME_TIME = 5 * 1000/ FPS; 
} 
Game::Game() { 
    SDL_Init(SDL_INIT_EVERYTHING); 
    this->gameLoop(); 
} 
Game::~Game() { 

} 
void Game::gameLoop() { 
    Graphics graphics; 
    Input input; 
    SDL_Event event; 

    this->_player = Player(graphics, 100, 100); 

    int LAST_UPDATE_TIME = SDL_GetTicks(); 
    //Start the game loop 
    while(true){ 
     input.beginNewFrame(); 

     if(SDL_PollEvent(&event)){ 
      if(event.type == SDL_KEYDOWN){ 
       if(event.key.repeat == 0){ 
        input.keyDownEvent(event); 
       } 
      } 
      else if(event.type == SDL_KEYUP){ 
       input.keyUpEvent(event); 
      } 
      else if(event.type == SDL_QUIT){ 
       return; 
      } 
     } 
     if(input.wasKeyPressed(SDL_SCANCODE_ESCAPE) == true){ 
      return; 
     } 
     else if(input.isKeyHeld(SDL_SCANCODE_LEFT) == true) { 
      this->_player.moveLeft(); 
     } 
     else if(input.isKeyHeld(SDL_SCANCODE_RIGHT) == true) { 
      this->_player.moveRight(); 
     } 

     if(!input.isKeyHeld(SDL_SCANCODE_LEFT) && !input.isKeyHeld(SDL_SCANCODE_RIGHT)){ 
      this->_player.stopMoving(); 
     } 

    const int CURRENT_TIME_MS = SDL_GetTicks(); 
    int ELAPSED_TIME_MS = CURRENT_TIME_MS - LAST_UPDATE_TIME; 
    this->update(std::min(ELAPSED_TIME_MS, MAX_FRAME_TIME)); 
    LAST_UPDATE_TIME = CURRENT_TIME_MS; 
this->draw(graphics); 
} 

} 
void Game::draw(Graphics &graphics){ 
    graphics.clear(); 

    this->_player.draw(graphics); 

    graphics.flip(); 

} 
void Game::update(float elapsedTime){ 
    this->_player.update(elapsedTime); 
} 

和player.cpp

#include "player.h" 
#include "graphics.h" 

namespace player_constants { 
    const float WALK_SPEED = 0.2f; 
} 

Player::Player() {} 

Player::Player(Graphics &graphics, float x, float y) : 
    AnimatedSprite(graphics, "MyChar.png", 0, 0, 16, 16, x, y, 100) 
    { 
     graphics.loadImage("MyChar.png"); 

     this->setupAnimations(); 
     this->playAnimation("RunRight"); 
    } 
void Player::setupAnimations() { 
    this->addAnimation(1, 0, 0, "IdleLeft", 16, 16, Vector2(0,0)); 
    this->addAnimation(1, 0, 16, "IdleRight", 16, 16, Vector2(0,0)); 
    this->addAnimation(3, 0, 0, "RunLeft", 16, 16, Vector2(0,0)); 
    this->addAnimation(3, 0, 16, "RunRight", 16, 16, Vector2(0,0)); 
} 

void Player::animationDone(std::string currentAnimation) {} 

void Player::moveLeft(){ 
    this->_dx = -player_constants::WALK_SPEED; 
    this->playAnimation("RunLeft"); 
    this->_facing = LEFT; 

} 
void Player::moveRight(){ 
    this->_dx = player_constants::WALK_SPEED; 
    this->playAnimation("RunRight"); 
    this->_facing = RIGHT; 

} 

void Player::stopMoving() { 
    this->_dx = 0.0f; 
    this->playAnimation(this->_facing == RIGHT ? "IdleRight" : "IdleLeft"); 
} 
void Player::update(float elapsedTime) { 
    //Move by dx 
    this->_x += this->_dx * elapsedTime; 

    AnimatedSprite::update(elapsedTime); 
} 

void Player::draw(Graphics &graphics) { 
    AnimatedSprite::draw(graphics, this->_x, this->_y); 
} 

的主要功能是 'moveLeft（）'， 'MoveRight的（）' 和 'stopMoving（）'上面的player.cpp文件。

我認爲在player.cpp文件中存在一些問題，任何人都可以幫助我解決這個問題，因爲我一直在嘗試修復問題超過3個小時。謝謝。

Answer 1

這個問題可能是由於每個循環只對一個事件進行輪詢，這意味着某些事件不會得到處理。您應該繼續輪詢事件，直到沒有更多事件排隊。有關獎金詳情，請參閱SDL docs。

在你的情況，你需要這樣的事情：

while(SDL_PollEvent(&event)){ 
    if(event.type == SDL_KEYDOWN){ 
     if(event.key.repeat == 0){ 
      input.keyDownEvent(event); 
     } 
    } 
    else if(event.type == SDL_KEYUP){ 
     input.keyUpEvent(event); 
    } 
    else if(event.type == SDL_QUIT){ 
     return; 
    } 
}