消失的 SDL 矩形。如何使用新的附加形状更新 window

Question

我试图在按下按键时用一个新的附加矩形更新 window，但由于 SDL_RenderClear，它一直在消失。是否建议删除 SDL_RenderClear？

while (!quit) {
  while (SDL_PollEvent( & e) != 0) {
    if (e.type == SDL_QUIT)
      quit = true;
  }
  SDL_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);
  SDL_RenderClear(gRenderer); //if i remove this line, the new rectangle will remain there

  SDL_Rect fillRect = {
    0,
    0,
    SCREEN_WIDTH / 5 - 5,
    SCREEN_HEIGHT / 5 - 5
  };
  SDL_SetRenderDrawColor(gRenderer, 255, 205, 51, 0xFF);
  SDL_RenderFillRect(gRenderer, & fillRect);

  switch (e.type) {
  case SDL_KEYDOWN:
    if (e.key.keysym.sym == SDLK_RIGHT) {
      SDL_Rect fillRect = {
        0,
        200,
        SCREEN_WIDTH / 5 - 5,
        SCREEN_HEIGHT / 5 - 5
      };
      SDL_SetRenderDrawColor(gRenderer, 255, 205, 51, 0xFF);
      SDL_RenderFillRect(gRenderer, & fillRect);
    }
    break;
  }
  SDL_RenderPresent(gRenderer);
}

Answer 1

SDL_RenderClear() 非常好，实际上您应该使用它。您的问题（又名矩形消失）是由您处理输入的方式引起的。 SDL_KEYDOWN 是一个事件，它只发生在您按下某个键的帧上，并且在短暂延迟后按住它。如果在那个确切的帧上按下了键，而不是在之前的任何帧上按下了键，那么您正在做的就是绘制矩形。通过 bool 的解决方案可能如下所示：

bool keyPressed = false;
while( !quit ) {
    while( SDL_PollEvent( &e ) != 0 ) {
        if( e.type == SDL_QUIT )
            quit = true; 
}
    SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
    SDL_RenderClear( gRenderer ); //if i remove this line, the new rectangle will remain there

    SDL_Rect fillRect = { 0, 0, SCREEN_WIDTH / 5-5, SCREEN_HEIGHT / 5-5 };
    SDL_SetRenderDrawColor( gRenderer, 255, 205, 51, 0xFF );        
    SDL_RenderFillRect( gRenderer, &fillRect );
    
    if(keyPressed){
        SDL_Rect fillRect = { 0, 200, SCREEN_WIDTH / 5-5, SCREEN_HEIGHT / 5-5 };
        SDL_SetRenderDrawColor( gRenderer, 255, 205, 51, 0xFF );        
        SDL_RenderFillRect( gRenderer, &fillRect );
}
    switch(e.type){
    case SDL_KEYDOWN:
        if(e.key.keysym.sym==SDLK_RIGHT){
            keyPressed = true;
        }
  break;
 }
   SDL_RenderPresent( gRenderer );
}

在图形中绝对应该清屏，否则您在之前帧中绘制的形状将保留在那里。

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