Lerking/gtk
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Merge branch 'final-frame-clock-work' into 'master'

Browse Source 
Final frame clock work

See merge request GNOME/gtk!2087
This commit is contained in:
Alexander Larsson
2020-06-15 10:27:02 +00:00
parent c49318e973 887aa2abdd
commit 1443ef85be
1 changed files with 127 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

151
gdk/gdkframeclockidle.c
View File

@@ -37,13 +37,25 @@
#define FRAME_INTERVAL 16667 /* microseconds */
typedef enum {
SMOOTH_PHASE_STATE_VALID = 0, /* explicit, since we count on zero-init */
SMOOTH_PHASE_STATE_AWAIT_FIRST,
SMOOTH_PHASE_STATE_AWAIT_DRAWN,
} SmoothDeltaState;
struct _GdkFrameClockIdlePrivate
{
gint64 frame_time; /* The exact time we last ran the clock cycle, or 0 if never */
gint64 smoothed_frame_time_base; /* A grid-aligned version of frame_time (grid size == refresh period), never more than half a grid from frame_time */
gint64 smoothed_frame_time_period; /* The grid size that smoothed_frame_time_base is aligned to */
gint64 smoothed_frame_time_reported; /* Ensures we are always monotonic */
gint64 smoothed_frame_time_phase; /* The offset of the first reported frame time, in the current animation sequence, from the preceding vsync */
gint64 min_next_frame_time; /* We're not synced to vblank, so wait at least until this before next cycle to avoid busy looping */
SmoothDeltaState smooth_phase_state; /* The state of smoothed_frame_time_phase - is it valid, awaiting vsync etc. Thanks to zero-init, the initial value
of smoothed_frame_time_phase is `0`. This is valid, since we didn't get a "frame drawn" event yet. Accordingly,
the initial value of smooth_phase_state is SMOOTH_PHASE_STATE_VALID. See the comment in gdk_frame_clock_paint_idle()
for details. */
gint64 sleep_serial;
gint64 freeze_time;
@@ -128,6 +140,7 @@ gdk_frame_clock_idle_init (GdkFrameClockIdle *frame_clock_idle)
gdk_frame_clock_idle_get_instance_private (frame_clock_idle);
priv->freeze_count = 0;
priv->smoothed_frame_time_period = FRAME_INTERVAL;
}
static void
@@ -334,23 +347,6 @@ maybe_stop_idle (GdkFrameClockIdle *clock_idle)
}
}
static gint64
compute_min_next_frame_time (GdkFrameClockIdle *clock_idle,
gint64 last_frame_time)
{
gint64 presentation_time;
gint64 refresh_interval;
gdk_frame_clock_get_refresh_info (GDK_FRAME_CLOCK (clock_idle),
last_frame_time,
&refresh_interval, &presentation_time);
if (presentation_time == 0)
return last_frame_time + refresh_interval;
else
return presentation_time + refresh_interval / 2;
}
static gboolean
gdk_frame_clock_flush_idle (void *data)
{
@@ -377,6 +373,25 @@ gdk_frame_clock_flush_idle (void *data)
return FALSE;
}
/*
* Returns the positive remainder.
*
* As an example, lets consider (-5) % 16:
*
* (-5) % 16 = (0 * 16) + (-5) = -5
*
* If we only want positive remainders, we can instead calculate
*
* (-5) % 16 = (1 * 16) + (-5) = 11
*
* The built-in `%` operator returns the former, positive_modulo() returns the latter.
*/
static int
positive_modulo (int i, int n)
{
return (i % n + n) % n;
}
static gboolean
gdk_frame_clock_paint_idle (void *data)
{
@@ -418,21 +433,88 @@ gdk_frame_clock_paint_idle (void *data)
priv->frame_time = g_get_monotonic_time ();
/*
* The first clock cycle of an animation might have been triggered by some external event. An external
* event can be an input event, an expired timer, data arriving over the network etc. This can happen at
* any time, so the cycle could have been scheduled at some random time rather then immediately after a
* frame completion. The offset between the start of the first animation cycle and the preceding vsync is
* called the "phase" of the clock cycle start time (not to be confused with the phase of the frame
* clock).
*
* In this first clock cycle, the "smooth" frame time is simply the time when the cycle was started. This
* could be followed by several cycles which are not vsync-related. As long as we don't get a "frame
* drawn" signal from the compositor, the clock cycles will occur every about frame_interval. Once we do
* get a "frame drawn" signal, from this point on the frame clock cycles will start shortly after the
* corresponding vsync signals, again every about frame_interval. The first vsync-related clock cycle
* might occur less than a refresh interval away from the last non-vsync-related cycle. See the diagram
* below for details. So while the cadence stays the same - a frame clock cycle every about frame_interval
* - the phase of the cycles start time has changed.
*
* Since we might have already reported the frame time to the application in the previous clock cycles, we
* have to adjust future reported frame times. We want the first vsync-related smooth time to be separated
* by exactly 1 frame_interval from the previous one, in order to maintain the regularity of the reported
* frame times. To achieve that, from this point on we add the phase of the first clock cycle start time to
* the smooth time. In order to compute that phase, accounting for possible skipped frames (e.g. due to
* compositor stalls), we want the following to be true:
*
* first_vsync_smooth_time = last_non_vsync_smooth_time + frame_interval * (1 + frames_skipped)
*
* We can assign the following known/desired values to the above equation:
*
* last_non_vsync_smooth_time = smoothed_frame_time_base
* first_vsync_smooth_time = frame_time + smoothed_frame_time_phase
*
* That leads us to the following, from which we can extract smoothed_frame_time_phase:
*
* frame_time + smoothed_frame_time_phase = smoothed_frame_time_base +
* frame_interval * (1 + frames_skipped)
*
* In the following diagram, '|' mark a vsync, '*' mark the start of a clock cycle, '+' is the adjusted
* frame time, '!' marks the reception of "frame drawn" events from the compositor. Note that the clock
* cycle cadence changed after the first vsync-related cycle. This cadence is kept even if we don't
* receive a 'frame drawn' signal in a subsequent frame, since then we schedule the clock at intervals of
* refresh_interval.
*
* vsync | | | | | |...
* frame drawn | | |! |! | |...
* cycle start | * | * |* |* |* |...
* adjusted times | * | * | + | + | + |...
* phase ^------^
*/
if (priv->smooth_phase_state == SMOOTH_PHASE_STATE_AWAIT_FIRST)
{
/* First animation cycle - usually unrelated to vsync */
priv->smoothed_frame_time_base = 0;
priv->smoothed_frame_time_phase = 0;
priv->smooth_phase_state = SMOOTH_PHASE_STATE_AWAIT_DRAWN;
}
else if (priv->smooth_phase_state == SMOOTH_PHASE_STATE_AWAIT_DRAWN &&
priv->paint_is_thaw)
{
/* First vsync-related animation cycle, we can now compute the phase. We want the phase to satisfy
0 <= phase < frame_interval */
priv->smoothed_frame_time_phase =
positive_modulo (priv->smoothed_frame_time_base - priv->frame_time,
frame_interval);
priv->smooth_phase_state = SMOOTH_PHASE_STATE_VALID;
}
if (priv->smoothed_frame_time_base == 0)
{
/* First frame */
priv->smoothed_frame_time_base = priv->frame_time;
priv->smoothed_frame_time_period = frame_interval;
/* First frame ever, or first cycle in a new animation sequence. Ensure monotonicity */
priv->smoothed_frame_time_base = MAX (priv->frame_time, priv->smoothed_frame_time_reported);
}
else
{
/* compute_smooth_frame_time() ensures monotonicity */
priv->smoothed_frame_time_base =
compute_smooth_frame_time (clock, priv->frame_time,
compute_smooth_frame_time (clock, priv->frame_time + priv->smoothed_frame_time_phase,
priv->paint_is_thaw,
priv->smoothed_frame_time_base,
priv->smoothed_frame_time_period);
priv->smoothed_frame_time_period = frame_interval;
}
priv->smoothed_frame_time_period = frame_interval;
priv->smoothed_frame_time_reported = priv->smoothed_frame_time_base;
_gdk_frame_clock_begin_frame (clock);
@@ -558,8 +640,19 @@ gdk_frame_clock_paint_idle (void *data)
*/
if (priv->freeze_count == 0)
{
priv->min_next_frame_time = compute_min_next_frame_time (clock_idle,
priv->smoothed_frame_time_base);
/*
* If we don't receive "frame drawn" events, smooth_cycle_start will simply be advanced in constant increments of
* the refresh interval. That way we get absolute target times for the next cycles, which should prevent skewing
* in the scheduling of the frame clock.
*
* Once we do receive "frame drawn" events, smooth_cycle_start will track the vsync, and do so in a more stable
* way compared to frame_time. If we then no longer receive "frame drawn" events, smooth_cycle_start will again be
* simply advanced in increments of the refresh interval, but this time we are in sync with the vsync. If we start
* receiving "frame drawn" events shortly after loosing them, then we should still be in sync.
*/
gint64 smooth_cycle_start = priv->smoothed_frame_time_base - priv->smoothed_frame_time_phase;
priv->min_next_frame_time = smooth_cycle_start + priv->smoothed_frame_time_period;
maybe_start_idle (clock_idle, FALSE);
}
@@ -598,6 +691,11 @@ gdk_frame_clock_idle_begin_updating (GdkFrameClock *clock)
}
#endif
if (priv->updating_count == 0)
{
priv->smooth_phase_state = SMOOTH_PHASE_STATE_AWAIT_FIRST;
}
priv->updating_count++;
maybe_start_idle (clock_idle, FALSE);
}
@@ -613,6 +711,11 @@ gdk_frame_clock_idle_end_updating (GdkFrameClock *clock)
priv->updating_count--;
maybe_stop_idle (clock_idle);
if (priv->updating_count == 0)
{
priv->smooth_phase_state = SMOOTH_PHASE_STATE_VALID;
}
#ifdef G_OS_WIN32
if (priv->updating_count == 0 && priv->begin_period)
{