Flickering background color - opengl

Question

I created an OpenGL window using SDL2 but the background keeps switching between black and yellow.
#include <SDL2/SDL.h>
#include <GL/glew.h>
#define SCREEN_WIDTH 500
#define SCREEN_HEIGHT 500
int main( int argc, char** argv )
{
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
SDL_GL_SetAttribute( SDL_GL_ACCELERATED_VISUAL, 1 );
SDL_Window* gWindow = SDL_CreateWindow(
"Title",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
SCREEN_WIDTH,
SCREEN_HEIGHT,
SDL_WINDOW_OPENGL);
SDL_GL_CreateContext( gWindow );
glewExperimental = GL_TRUE;
glewInit();
glPointSize(3);
glClearColor(1,1,0,0);
glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
glClear(GL_COLOR_BUFFER_BIT);
SDL_GL_SetSwapInterval(1);
int quit=0;
SDL_Event event;
while( !quit )
{
while(SDL_PollEvent( &event ))
{
if( event.type == SDL_QUIT )
quit = 1;
}
SDL_GL_SwapWindow( gWindow );
}
SDL_DestroyWindow(gWindow);
return 0;
}
I expect the background to be yellow, as defined with glClearColor(1,1,0,0), without flickering while the program runs. Is there something wrong in the code?

Answer 1

The reason for flickering is that you're using double buffering but do not clear one of the buffers with the yellow color (i.e. note that you're calling glClear only once in your code).
I suggest you call glClear every frame. To fix your code, you can move the call into the loop, just before the SDL_GL_SwapWindow:
while( !quit )
{
while(SDL_PollEvent( &event ))
{
if( event.type == SDL_QUIT )
quit = 1;
}
glClear(GL_COLOR_BUFFER_BIT);
SDL_GL_SwapWindow( gWindow );
}