testcase for SDL2 bug #4152 (and the old #3931)

warptest.c

// gcc -Wall -o warptest `sdl2-config --cflags` warptest.c `sdl2-config --libs`

#include <stdio.h>
#include <SDL.h>

static FILE* outfile = NULL;

static void UpdateWinTitle(int accumX, int accumY, SDL_Window* win)
{
	char buf[128];
	snprintf(buf, 128, "Accumulated: X: %d Y: %d    (Press Q to quit)\n", accumX, accumY);
	SDL_SetWindowTitle(win, buf);
}

int main(int argc, char** argv)
{
	outfile = stdout;
	//outfile = fopen("warptest.log", "wt");

	SDL_Init(SDL_INIT_VIDEO);
	SDL_Window* win = SDL_CreateWindow("Move your mouse! (Press Q to quit)", 100, 100, 640, 480, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);

	SDL_Surface* winSurf = SDL_GetWindowSurface(win);
	Uint32 grey = SDL_MapRGB(winSurf->format, 127, 127, 127);

	if(argc > 1 && strcmp(argv[1], "-raw") == 0) {
		fprintf(outfile, "Using default raw mouse input for relative mouse mode (unless RegisterRawInputDevices() failed)\n");
	} else {
		fprintf(outfile, "Setting SDL_HINT_MOUSE_RELATIVE_MODE_WARP 1 => using mouse warp for relative mouse mode\n");
		SDL_SetHint(SDL_HINT_MOUSE_RELATIVE_MODE_WARP, "1");
	}
	fflush(outfile);

	SDL_SetRelativeMouseMode(1);

	// accum* holds the sum of all relative movements and is shown in window title
	int accumX = 0, accumY = 0;

	int keepRunning = 1;
	while(keepRunning) {
		SDL_Delay(7); // real games would do something useful (game logic) here..
		
		winSurf = SDL_GetWindowSurface(win);
		SDL_FillRect(winSurf, NULL, grey);
		SDL_UpdateWindowSurface(win);
		
		SDL_Event ev;
		while(SDL_PollEvent(&ev)) {
			switch(ev.type) {
				case SDL_KEYDOWN:
					if(ev.key.keysym.sym == SDLK_q || ev.key.keysym.sym == SDLK_ESCAPE) {
						fprintf(outfile, "You pressed Q  or Esc - bye!\n");
						keepRunning = 0;
					}
					break;
				case SDL_MOUSEMOTION:
					if(ev.motion.xrel > 0)
						fprintf(outfile, "> Mouse motion: rel: %d %d pos: %d %d\n", (int)ev.motion.xrel, (int)ev.motion.yrel, (int)ev.motion.x, (int)ev.motion.y);
					else
						fprintf(outfile, "<<< Mouse motion: rel: %d %d pos: %d %d\n", (int)ev.motion.xrel, (int)ev.motion.yrel, (int)ev.motion.x, (int)ev.motion.y);
					
					fflush(outfile);
					
					accumX += ev.motion.xrel;
					accumY += ev.motion.yrel;
					UpdateWinTitle(accumX, accumY, win);
					break;
				
			}
		}
		//fprintf(outfile, "### end of frame ###\n");
		//fflush(outfile);
	}

	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}