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SDL2 flickering rect. Unclear how to properly use SDL_RenderClear

ikruz98 (2)
Sorry if this post is in the incorrect spot or if i have formatted this post incorrectly, i am new to posting in forums. if i did something incorrectly with this post, please point it out and ill fix it as soon as i can.

im currently working on a self teaching project using SDL2 to create pong. I have been using sfml and i decided to give sdl a go as i wanted to get my feet wet in openGL like programming. I have managed to draw the paddles and implement movement but sometimes the paddles flicker and i believe that i am using SDL_RenderClear incorrectly or in the wrong place


Paddle.cpp
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#include "Paddle.h"
#include <iostream>



Paddle::Paddle(SDL_Window* window)
{
}


Paddle::~Paddle()
{
}

void Paddle::SetUp(int x, int y, int width, int height)
{
	paddle1.x = x;
	paddle1.y = y;
	paddle1.w = width;
	paddle1.h = height;
}

void Paddle::Draw(SDL_Renderer* renderer)
{
	SDL_SetRenderDrawColor(renderer, 255,255,255,255);
	SDL_RenderFillRect(renderer, &paddle1);
	SDL_RenderPresent(renderer);
}

void Paddle::MoveUp(float speed, SDL_Renderer* renderer)
{
	this->paddle1.y -= 1 * speed;
	SDL_RenderFillRect(renderer, &paddle1);
	std::cout << "W\n";
}

void Paddle::MoveDown(float speed, SDL_Renderer * renderer)
{
	this->paddle1.y += 1 * speed;
	SDL_RenderFillRect(renderer, &paddle1);
	std::cout << "S\n";
}

void Paddle::MouseMove(float speed, SDL_Renderer * renderer, SDL_MouseMotionEvent mouse)
{
	
	this->paddle1.y = mouse.y;
	SDL_RenderFillRect(renderer, &paddle1);
	std::cout << "S\n";
}


Game.cpp
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#include "Game.h"



Game::Game()
{
	gameState = STATE::PLAY;
}


Game::~Game()
{
	SDL_Quit();
}

void Game::Init(int width, int height, std::string title)
{
	SDL_Init(SDL_INIT_EVERYTHING);
	const char* cTitle;
	cTitle = title.c_str();
	window = SDL_CreateWindow(
		cTitle, 
		SDL_WINDOWPOS_UNDEFINED, 
		SDL_WINDOWPOS_UNDEFINED, 
		width, 
		height, 
		SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);

	renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
	

	player1.SetUp(5, height / 2, 20, 100);
	player2.SetUp(width - 25, height / 2, 20, 100);



	//SDL CHECK ERROR
	InitErrorCheck();
}

void Game::Update()
{
	while (gameState != STATE::EXIT)
	{
		SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
		SDL_RenderClear(renderer);

		CheckInput();
		Destroy();
		player1.Draw(renderer);
		player2.Draw(renderer);
	}
}

void Game::Run()
{
	Init(800,600,"Pong");
	Update();

}

void Game::InitErrorCheck()
{
	if (SDL_Init(SDL_INIT_EVERYTHING) < 0)
	{
		printf("Error Initializing SDL: %s\n", SDL_GetError());
		exit(1);
	}



	if (window == NULL)
	{
		printf("Error Creating Window: %s\n", SDL_GetError());
		exit(1);
	}

	if (renderer == NULL)
	{
		printf("Error Creating Renderer %s\n", SDL_GetError());
	}
}

void Game::CheckInput()
{
	SDL_Event evnt;
	while (SDL_PollEvent(&evnt) == 1)
	{
		switch (evnt.type)
		{
		case SDL_QUIT:
			gameState = STATE::EXIT;
			break;
		case SDL_MOUSEMOTION:
			player1.MouseMove(5, renderer, evnt.motion);
			player2.MouseMove(5, renderer, evnt.motion);
			//std::cout << evnt.motion.x << " " << evnt.motion.y << std::endl;
			break;
		case SDL_KEYDOWN:
			switch (evnt.key.keysym.sym)
			{
			case SDLK_w:
				player1.MoveUp(5, renderer);
				break;
			case SDLK_s:
				player1.MoveDown(5, renderer);
				break;
			}
		}
	
		
	}
}

//Free resources with this function
void Game::Destroy()
{
	if (gameState == STATE::EXIT)
		SDL_Quit();
	if (renderer == NULL)
		SDL_DestroyRenderer(renderer);

}


Any criticism is welcome and any tips would be appreciated as i still consider myself a complete beginner :)
Last edited on
helios (17575)
You're calling SDL_RenderPresent() inside Paddle::Draw(), which swaps the screen buffers. You should only call that function once you're done rendering the entire current frame.
ikruz98 (2)
wow thanks alot helios, that fixed my problem. much appreciated :)
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