Creating, Deleting and Recreating a SDL GL Context stops Mouse events

[Evengard]

This seems to be a regression since v17, as the bug didn't existed in v17.
In v18, when doing

ctx = SDL_GL_CreateContext(wnd);
SDL_GL_DeleteContext(ctx);
ctx = SDL_GL_CreateContext(wnd);

this stops mouse events from being dispatched via SDL_PollEvent. They just doesn't appear no matter what do I do.
The bug is nonexistant in non-EMSCRIPTEN environment (i.e. when built with SDL on Windows)

[Daft-Freak]

Hmm, I couldn't reproduce with this:

// emcc -s USE_SDL=2
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif

#include "SDL.h"

#include <stdio.h>

static int run = 1;

SDL_Window *window;

void loop() {
  SDL_Event event;
  while (SDL_PollEvent(&event)) {
    switch(event.type) {

    case SDL_MOUSEMOTION:
      printf("motion %i %i\n", event.motion.x, event.motion.y);
      break;

    case SDL_QUIT:
      run = 0;
      break;
    }
  }
}

int main(int argc, char *argv[]) {
  if (SDL_Init(SDL_INIT_VIDEO) < 0) {
    return (1);
  }

  window = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, 0);

  SDL_GLContext ctx = SDL_GL_CreateContext(window);
  SDL_GL_DeleteContext(ctx);
  ctx = SDL_GL_CreateContext(window);

#ifdef __EMSCRIPTEN__
  emscripten_set_main_loop(loop, 0, 1);
#else
  while (run) loop();
#endif

  return (0);
}

Also, if it helps narrow this down, these are the non-upstream changes between 17 and 18: version_17...3a222fc (the rest is 2.0.7 -> 2.0.9)

[Evengard]

I'll try to test with only theese changes later. My app is a lot bigger and is kinda legacy stuff, hard to pinpoint the exact cause, but removing the SDL_GLContext recreation fixed it. So I guess this is somewhere around there.

Also, the actual delete and recreate happens in the main loop. And also, the mouse is set as relative.

[six809]

I'm also having this problem, though I don't set up contexts directly, I use renderers. If you destroy one and recreate another one for the same window, mouse events vanish. Modifying your example:

// emcc -s USE_SDL=2
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif

#include "SDL.h"

#include <stdio.h>

static int run = 1;

SDL_Window *window;
SDL_Renderer *renderer;

void loop() {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
                switch(event.type) {

                case SDL_MOUSEMOTION:
                        printf("motion %i %i\n", event.motion.x, event.motion.y);
                        break;

                case SDL_QUIT:
                        run = 0;
                        break;
                }
        }
}

int main(int argc, char *argv[]) {
        if (SDL_Init(SDL_INIT_VIDEO) < 0) {
                return (1);
        }

        window = SDL_CreateWindow("Test", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);

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

        // Comment these out and it works...
        SDL_DestroyRenderer(renderer);
        renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);

#ifdef __EMSCRIPTEN__
        emscripten_set_main_loop(loop, 0, 1);
#else
        while (run) loop();
#endif

        return (0);
}

[Daft-Freak]

Hmm, just destroying the renderer is enough... Digging down a bit, it looks like Emscripten removes ALL event handlers from a canvas when you destroy a GL context: https://github.com/emscripten-core/emscripten/blob/master/src/library_webgl.js#L999.

[six809]

Ah, I guess that's this, then: emscripten-core/emscripten#9803

Seems I can work around it myself by just not recreating the renderer. I thought I was doing that because I had to on window resize, but it seems to work fine in Linux, emscripten, Windows (well, Wine). Not tested macosx yet.

Edit: I was wrong. It is needed when resizing, or you get some strange scaling effects.