SDL2 window created with SDL_WINDOW_FULLSCREEN_DESKTOP won't change display mode when changing to SDL_WINDOW_FULLSCREEN

[nmlgc]

Tested at 643437f on Windows 11. A non-fullscreen window can switch into borderless and then exclusive fullscreen mode without issue:

#include <SDL.h>
#include <assert.h>

int main(void)
{
	int ret = 0;
	SDL_Init(SDL_INIT_VIDEO);
	SDL_CreateWindowAndRenderer(640, 480, 0, &window, &renderer);

	SDL_SetRenderDrawColor(renderer, 0, 0, 128, SDL_ALPHA_OPAQUE);
	SDL_RenderFillRect(renderer, NULL);
	SDL_RenderPresent(renderer);
	SDL_Delay(1000);

	ret = SDL_SetWindowFullscreen(window, SDL_WINDOW_FULLSCREEN_DESKTOP);
	assert(ret == 0);
	SDL_SetRenderDrawColor(renderer, 128, 0, 0, SDL_ALPHA_OPAQUE);
	SDL_RenderFillRect(renderer, NULL);
	SDL_RenderPresent(renderer);
	SDL_Delay(1000);

	ret = SDL_SetWindowFullscreen(window, SDL_WINDOW_FULLSCREEN);
	assert(ret == 0);
	SDL_SetRenderDrawColor(renderer, 0, 128, 0, SDL_ALPHA_OPAQUE);
	SDL_RenderFillRect(renderer, NULL);
	SDL_RenderPresent(renderer);
	SDL_Delay(5000);
	
	return 0;
}

If the window is created in borderless mode though, it stays locked to the desktop resolution and the switch to SDL_WINDOW_FULLSCREEN won't perform a display mode change:

#include <SDL.h>
#include <assert.h>

int main(void)
{
	int ret = 0;
	SDL_Window *window = NULL;
	SDL_Renderer *renderer = NULL;

	SDL_Init(SDL_INIT_VIDEO);
	SDL_CreateWindowAndRenderer(
		640, 480, SDL_WINDOW_FULLSCREEN_DESKTOP, &window, &renderer
	);

	SDL_SetRenderDrawColor(renderer, 0, 0, 128, SDL_ALPHA_OPAQUE);
	SDL_RenderFillRect(renderer, NULL);
	SDL_RenderPresent(renderer);
	SDL_Delay(1000);
	
	/// Even switching into windowed mode beforehand does not help.
	// SDL_SetWindowFullscreen(window, 0);
	// SDL_Delay(2000);

	ret = SDL_SetWindowFullscreen(window, SDL_WINDOW_FULLSCREEN); // ← has no effect?
	assert(ret == 0);

	SDL_SetRenderDrawColor(renderer, 128, 0, 0, SDL_ALPHA_OPAQUE);
	SDL_RenderFillRect(renderer, NULL);
	SDL_RenderPresent(renderer);

	SDL_Delay(1000);
	SDL_Quit();

	return 0;
}

The equivalent SDL 3 code also works without issue.

[slouken]

Sorry, I put this in the wrong milestone, but I highly recommend switching to SDL3 or using sdl2-compat if that's a possibility for you.