Disable the invocation of poll for backends

The internal event handling relied on the poll(2) for monitoring X11
events via I/O multiplexing. However, for backends such as SDL, this
manipulation causes problems since the internal file descriptors
associated with underlying system events are hidden and not exposed.
Thus, we should avoid polling the file descriptors. Instead, let the
backend handle the event loop when possible.

Author: jserv

backend/sdl.c

@@ -133,8 +133,7 @@ twin_sdl_t *twin_sdl_create(int width, int height)
     tx->screen = twin_screen_create(width, height, _twin_sdl_put_begin,
                                     _twin_sdl_put_span, tx);
 
-    twin_set_file(twin_sdl_read_events, SDL_GetWindowDisplayIndex(tx->win),
-                  TWIN_READ, tx);
+    twin_set_file(twin_sdl_read_events, 0, TWIN_READ, tx);
 
     twin_set_work(twin_sdl_work, TWIN_WORK_REDISPLAY, tx);
 
@@ -174,7 +173,7 @@ bool twin_sdl_process_events(twin_sdl_t *tx)
     bool result;
 
     _twin_run_work();
-    result = twin_sdl_read_events(SDL_GetWindowDisplayIndex(tx->win), 0, tx);
+    result = twin_sdl_read_events(0, 0, tx);
     _twin_run_work();
 
     return result;

src/file.c

@@ -5,9 +5,12 @@
  */
 
 #include <assert.h>
-#include <sys/poll.h>
 #include <unistd.h>
 
+#ifdef USE_POLL
+#include <sys/poll.h>
+#endif
+
 #include "twinint.h"
 
 static twin_queue_t *head;
@@ -31,15 +34,16 @@ int _twin_run_file(twin_time_t delay)
     int n;
     int i;
     int r;
-    short events;
-    twin_file_op_t op;
+#ifdef USE_POLL
     struct pollfd *polls;
+#endif
 
     first = (twin_file_t *) _twin_queue_set_order(&head);
     if (first) {
         for (file = first, n = 0; file;
              file = (twin_file_t *) file->queue.order, n++)
             ;
+#ifdef USE_POLL
         polls = malloc(n * sizeof(struct pollfd));
         if (!polls)
             return 1;
@@ -56,20 +60,29 @@ int _twin_run_file(twin_time_t delay)
         }
         r = poll(polls, n, delay);
         if (r > 0)
+#endif
             for (file = first, i = 0; file;
                  file = (twin_file_t *) file->queue.order, i++) {
-                events = polls[i].revents;
+                twin_file_op_t op = 0;
+#ifdef USE_POLL
+                short events = polls[i].revents;
                 assert(polls[i].fd == file->file);
-                op = 0;
                 if (events & POLLIN)
                     op |= TWIN_READ;
                 if (events & POLLOUT)
                     op |= TWIN_WRITE;
-                if (op && !(*file->proc)(file->file, op, file->closure))
+#endif
+                if (
+#ifdef USE_POLL
+                    op &&
+#endif
+                    !(*file->proc)(file->file, op, file->closure))
                     _twin_queue_delete(&head, &file->queue);
             }
         _twin_queue_review_order(&first->queue);
+#ifdef USE_POLL
         free(polls);
+#endif
         return 1;
     } else {
         if (delay > 0)