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flash mitigation: add a small delay before rendering after receiving client data

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Simply re-trying to read client data is not enough in many
cases. Re-work the flash mitigation to instead incur a small delay
before rendering.
This commit is contained in:
Daniel Eklöf 2019-07-04 09:54:40 +02:00
parent 03ca7a04ab
commit ef944933e6
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GPG key ID: 5BBD4992C116573F
1 changed files with 52 additions and 13 deletions
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65
main.c
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@ -1003,6 +1003,8 @@ main(int argc, char *const *argv)
}
}
int timeout_ms = -1;
while (true) {
struct pollfd fds[] = {
{.fd = wl_display_get_fd(c.wl.display), .events = POLLIN},
@ -1011,7 +1013,21 @@ main(int argc, char *const *argv)
};
wl_display_flush(c.wl.display);
poll(fds, sizeof(fds) / sizeof(fds[0]), -1);
int ret = poll(fds, sizeof(fds) / sizeof(fds[0]), timeout_ms);
if (ret == -1) {
LOG_ERRNO("failed to poll file descriptors");
break;
}
if (ret == 0 || !(timeout_ms != -1 && fds[1].revents & POLLIN)) {
/* Delayed rendering */
if (!c.frame_is_scheduled)
grid_render(&c);
}
/* Reset poll timeout to infinity */
timeout_ms = -1;
if (fds[0].revents & POLLIN) {
wl_display_dispatch(c.wl.display);
@ -1027,20 +1043,43 @@ main(int argc, char *const *argv)
}
if (fds[1].revents & POLLIN) {
for (size_t i = 0; i < 3; i++) {
uint8_t data[8192];
ssize_t count = read(c.term.ptmx, data, sizeof(data));
if (count < 0) {
if (errno != EAGAIN)
LOG_ERRNO("failed to read from pseudo terminal");
break;
}
vt_from_slave(&c.term, data, count);
uint8_t data[8192];
ssize_t count = read(c.term.ptmx, data, sizeof(data));
if (count < 0) {
if (errno != EAGAIN)
LOG_ERRNO("failed to read from pseudo terminal");
break;
}
if (!c.frame_is_scheduled)
grid_render(&c);
vt_from_slave(&c.term, data, count);
/*
* We likely need to re-render. But, we don't want to do
* it immediately. Often, a single client operation is
* done through multiple writes. Many times, we're so fast
* that we render mid-operation frames.
*
* For example, we might end up rendering a frame where
* the client just erased a line, while in the next frame,
* the client wrote to the same line. This causes screen
* "flashes".
*
* Mitigate by always incuring a small delay before
* rendering the next frame. This gives the client some
* time to finish the operation (and thus gives us time to
* receive the last writes before doing any actual
* rendering).
*
* Note that when the client is producing data at a very
* high pace, we're rate limited by the wayland compositor
* anyway. The delay we introduce here only has any effect
* when the renderer is idle.
*
* TODO: this adds input latency. Can we somehow hint
* ourselves we just received keyboard input, and in this
* case *not* delay rendering?
*/
timeout_ms = 1;
}
if (fds[1].revents & POLLHUP) {