Kristian Høgsberg wrote:
+ * A correct sequence would be:
+ *
+ * while (wl_display_prepare_read(display) != 0)
+ * wl_display_dispatch_pending(display);
+ * wl_display_flush(display);
+ * poll(fds, nfds, -1);
+ * wl_display_read_events(display);
+ * wl_display_dispatch_pending(display);
When writing a client I need to do "idle" effects (what Qt calls
"aboutToBlock"), in particular redrawing all damaged surfaces. This may
trigger more events so it has to be in the prepare loop. I need to
remove the second dispatch, because I need to make sure draw is called
if any events are handled but I don't want to call it an extra time if
prepare indicates more events. This also I think removes a redundant
test for pending events that is repeated by the prepare_read():
mainloop() {
for (;;) {
while (wl_display_prepare_read(display) != 0) {
wl_display_dispatch_pending(display);
draw_damaged_surfaces();
}
wl_display_flush(display);
poll(fds, nfds, -1);
wl_display_read_events(display);
}
}
Now I'm wondering if dispatch_pending is *ever* called without the
prepare_read(). Perhaps these can be replaced with a single function
that is the equivalent of:
wl_foo(display) {
if (wl_display_prepare_read(display)) {
wl_display_dispatch_pending(display);
return true;
} else {
return false;
}
}
And the main loop looks like this:
mainloop() {
for (;;) {
while (wl_foo(display))
draw_damaged_surfaces();
wl_display_flush(display);
poll(fds, nfds, -1);
wl_display_read_events(display);
}
}
If clients have to register the idle callback then this function could
do the loop as well, which may be more efficient and allows error
indicators to be returned. I think it could even do a blocking
read_events() and the display_flush(). Then the main loop looks like this:
mainloop() {
wl_add_idle_callback(draw_damaged_surfaces);
for (;;) {
poll(fds, nfds, -1);
if (wl_foo()) abort();
}
}
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