Window Changes Color Over Time In SDL2 - c++

Question

I've created a window in SDL2 that opens in the color red. I need the window to change color after a few seconds and continue to do so as long as the window is open. So the window may open red, stay for five seconds then become green for five seconds then become blue for five seconds then loop back to red and begin the whole process again.
int WindowOpen() {
bool quit = false;
SDL_Window *window; // Declare a pointer
SDL_Init(SDL_INIT_VIDEO); // Initialize SDL2
// Create an application window with the following settings:
window = SDL_CreateWindow(
"My SDL2 window", // window title
SDL_WINDOWPOS_UNDEFINED, // initial x position
SDL_WINDOWPOS_UNDEFINED, // initial y position
640, // width, in pixels
480, // height, in pixels
SDL_WINDOW_OPENGL // flags - see below
);
SDL_Renderer *renderer = NULL;
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
SDL_Event* MainEvent = new SDL_Event();
SDL_RenderClear(renderer);
// Up until now everything was drawn behind the scenes.
// This will show the new, red contents of the window.
SDL_RenderPresent(renderer);
// Check that the window was successfully created
if (window == NULL) {
// In the case that the window could not be made...
printf("Could not create window: %s\n", SDL_GetError());
return 1;
}
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);//red. Was testing to see if window would open red and change to green then blue but this doesn't work.
//SDL_Delay(3000);
//SDL_SetRenderDrawColor(renderer, 300, 150, 0, 155);//green
//SDL_Delay(3000);
//SDL_SetRenderDrawColor(renderer, 129, 150, 500, 105);//blue
while (quit == false && MainEvent->type != SDL_QUIT) { //While quit is false, run window and renderer.
SDL_PollEvent(MainEvent);
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
}
// The window is open: could enter program loop here (see SDL_PollEvent())
//SDL_Delay(3000); // Pause execution for 3000 milliseconds, for example
// Close and destroy the window
SDL_DestroyWindow(window);
SDL_DestroyRenderer(renderer);
delete MainEvent;
// Clean up
SDL_Quit();
}

Answer 1

SDL_SetRenderDrawColor is just setting the colour the renderer would paint, if you asked it to. To fill the back buffer with that colour you should follow it up with SDL_RenderClear. With the back buffer filled, to then draw it on the screen you need to call SDL_RenderPresent.
while (quit == false && MainEvent->type != SDL_QUIT) { //While quit is false, run window and renderer.
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);//red. Was testing to see if window would open red and change to green then blue but this doesn't work.
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
SDL_Delay(3000);
SDL_SetRenderDrawColor(renderer, 300, 150, 0, 155);//green
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
SDL_Delay(3000);
SDL_SetRenderDrawColor(renderer, 129, 150, 500, 105);//blue
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
SDL_Delay(3000);
SDL_PollEvent(MainEvent);
}
Changing your main loop to something like that will do similar to what you want, but the delay is three seconds. Also, this way your main loop will take 9 seconds to execute, which means event handling for quit could take up to 9 seconds. This isn't very good, but fixing it is left as an exercise for the reader.