Dissapearing SDL Rects. How to update window with new additional shapes - c++

Question

I'm trying to update the window with a new additional rect upon key pressing, but it keeps disappearing due to SDL_RenderClear. Is it recommended to remove 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() is perfectly fine and in fact you should be using it. Your problem (aka the rect disappearing) is caused by the way you handle input. SDL_KEYDOWN is an event that only occurs on the frame that you press a key for, and while you're holding it down after a short delay. What you are doing is drawing the rect if the key has been pressed on that exact frame, not if it's been pressed on any previous frames. A solution via a bool could look like this:
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 );
}
Screen clearing is something that should absolutely be done in graphics, because otherwise the shapes you've drawn on previous frames will just remain there.