12to11/frame_clock.c

/* Wayland compositor running on top of an X server.

Copyright (C) 2022 to various contributors.

This file is part of 12to11.

12to11 is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.

12to11 is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with 12to11.  If not, see <https://www.gnu.org/licenses/>.  */

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#include "compositor.h"

typedef struct _FrameClockCallback FrameClockCallback;
typedef struct _CursorClockCallback CursorClockCallback;

enum
  {
    /* 150ms.  */
    MaxPresentationAge = 150000,
  };

/* Major and minor versions of the XSync extension.  */

static int xsync_major, xsync_minor;

/* Whether or not the compositor supports frame synchronization.  */

static Bool frame_sync_supported;

/* Timer used for cursor animations.  */

static Timer *cursor_clock;

/* How many cursors want cursor animations.  */

static int cursor_count;

struct _FrameClockCallback
{
  /* Function called once a frame is completely written to display and
     (ideally, whether or not this actually works depends on various
     different factors) enters vblank.  */
  void (*frame) (FrameClock *, void *);

  /* Data that function is called with.  */
  void *data;

  /* Next and last callbacks in this list.  */
  FrameClockCallback *next, *last;
};

struct _FrameClock
{
  /* List of frame clock callbacks.  */
  FrameClockCallback callbacks;

  /* Two sync counters.  */
  XSyncCounter primary_counter, secondary_counter;

  /* The value of the frame currently being drawn in this frame clock,
     and the value of the last frame that was marked as complete.  */
  uint64_t next_frame_id, finished_frame_id;

  /* Whether or not we are waiting for a frame to be completely
     painted.  */
  Bool in_frame;

  /* A timer used as a fake synchronization source if frame
     synchronization is not supported.  */
  Timer *static_frame_timer;

  /* A timer used to end the next frame.  */
  Timer *end_frame_timer;

  /* Whether or not configury is in progress, and whether or not this
     is frozen, and whether or not the frame shouldn't actually be
     unfrozen until EndFrame.  */
  Bool need_configure, frozen, frozen_until_end_frame;

  /* The wanted configure value.  */
  uint64_t configure_id;

  /* The time the last frame was drawn.  */
  uint64_t last_frame_time;

  /* The presentation time.  */
  int32_t presentation_time;

  /* The refresh interval.  */
  uint32_t refresh_interval;

  /* Whether or not this frame clock should try to predict
     presentation times, in order to group frames together.  */
  Bool predict_refresh;

  /* Callback run when the frame is frozen.  */
  void (*freeze_callback) (void *);

  /* Data for that callback.  */
  void *freeze_callback_data;
};

struct _CursorClockCallback
{
  /* Function called every time cursors should animate once.  */
  void (*frame) (void *, struct timespec);

  /* Data for that function.  */
  void *data;

  /* Next and last cursor clock callbacks.  */
  CursorClockCallback *next, *last;
};

/* List of cursor frame callbacks.  */

static CursorClockCallback cursor_callbacks;

static void
SetSyncCounter (XSyncCounter counter, uint64_t value)
{
  uint64_t low, high;
  XSyncValue sync_value;

  low = value & 0xffffffff;
  high = value >> 32;

  XSyncIntsToValue (&sync_value, low, high);
  XSyncSetCounter (compositor.display, counter,
		   sync_value);
}

static uint64_t
CurrentHighPrecisionTimestamp (void)
{
  struct timespec clock;
  uint64_t timestamp;

  clock_gettime (CLOCK_MONOTONIC, &clock);

  if (IntMultiplyWrapv (clock.tv_sec, 1000000, &timestamp)
      || IntAddWrapv (timestamp, clock.tv_nsec / 1000, &timestamp))
    /* Overflow.  */
    return 0;

  return timestamp;
}

static Bool
HighPrecisionTimestampToTimespec (uint64_t timestamp,
				  struct timespec *timespec)
{
  uint64_t remainder, seconds;

  seconds = timestamp / 1000000;
  remainder = timestamp % 1000000;

  if (IntAddWrapv (0, seconds, &timespec->tv_sec))
    return False;

  /* We know that this cannot overflow tv_nsec, which is long int.  */
  timespec->tv_nsec = remainder * 1000;
  return True;
}

/* Forward declaration.  */

static void EndFrame (FrameClock *);

static void
HandleEndFrame (Timer *timer, void *data, struct timespec time)
{
  FrameClock *clock;

  clock = data;

  /* Now that the time allotted for the current frame has run out, end
     the frame.  */
  RemoveTimer (timer);
  clock->end_frame_timer = NULL;
  EndFrame (clock);
}

static void
PostEndFrame (FrameClock *clock)
{
  uint64_t target, now;
  struct timespec timespec;

  XLAssert (clock->end_frame_timer == NULL);

  if (!clock->refresh_interval
      || !clock->presentation_time)
    return;

  /* Calculate the time by which the next frame must be drawn.  It is
     a multiple of the refresh rate with the vertical blanking
     period added.  */
  target = clock->last_frame_time + clock->presentation_time;
  now = CurrentHighPrecisionTimestamp ();

  if (!now)
    return;

  /* If the last time the frame time was obtained was that long ago,
     return immediately.  */
  if (now - clock->last_frame_time >= MaxPresentationAge)
    return;

  while (target < now)
    {
      if (IntAddWrapv (target, clock->refresh_interval, &target))
	return;
    }

  /* Convert the high precision timestamp to a timespec.  */
  if (!HighPrecisionTimestampToTimespec (target, &timespec))
    return;

  /* Use 3/4ths of the presentation time.  Any more and we risk the
     counter value change signalling the end of the frame arriving
     after the presentation deadline.  */
  target = target - (clock->presentation_time / 4 * 3);

  /* Schedule the timer marking the end of this frame for the target
     time.  */
  clock->end_frame_timer = AddTimerWithBaseTime (HandleEndFrame,
						 clock,
						 /* Use no delay; this
						    timer will only
						    run once.  */
						 MakeTimespec (0, 0),
						 timespec);
}

static void
StartFrame (FrameClock *clock, Bool urgent, Bool predict)
{
  if (clock->frozen)
    return;

  if (clock->frozen_until_end_frame)
    return;

  if (clock->need_configure)
    {
      clock->next_frame_id = clock->configure_id;
      clock->finished_frame_id = 0;
    }

  clock->in_frame = True;

  /* Set the clock to an odd value; if we want the compositor to
     redraw this frame immediately (since it is running late), make it
     so that value % 4 == 3.  Otherwise, make it so that value % 4 ==
     1.  */

  if (urgent)
    {
      if (clock->next_frame_id % 4 == 2)
	clock->next_frame_id += 1;
      else
	clock->next_frame_id += 3;
    }
  else
    {
      if (clock->next_frame_id % 4 == 3)
	clock->next_frame_id += 3;
      else
	clock->next_frame_id += 1;
    }

  /* If frame synchronization is not supported, setting the sync
     counter itself isn't necessary; the values are used as a flag to
     tell us whether or not a frame has been completely drawn.  */
  if (!frame_sync_supported)
    return;

  SetSyncCounter (clock->secondary_counter,
		  clock->next_frame_id);

  if (clock->predict_refresh && predict)
    PostEndFrame (clock);

  clock->need_configure = False;
}

static void
EndFrame (FrameClock *clock)
{
  if (clock->frozen)
    return;

  clock->frozen_until_end_frame = False;

  if (!clock->in_frame
      /* If the end of the frame has already been signalled, this
	 function should just return instead of increasing the counter
	 to an odd value.  */
      || clock->finished_frame_id == clock->next_frame_id)
    return;

  if (clock->end_frame_timer)
    /* If the frame is ending at a predicted time, don't allow ending
       it manually.  */
    return;

  /* Signal to the compositor that the frame is now complete.  When
     the compositor finishes drawing the frame, a callback will be
     received.  */
  clock->next_frame_id += 1;
  clock->finished_frame_id = clock->next_frame_id;

  if (!frame_sync_supported)
    return;

  SetSyncCounter (clock->secondary_counter,
		  clock->next_frame_id);
}

static void
FreeFrameCallbacks (FrameClock *clock)
{
  FrameClockCallback *callback, *last;

  callback = clock->callbacks.next;

  while (callback != &clock->callbacks)
    {
      last = callback;
      callback = callback->next;

      XLFree (last);
    }

  clock->callbacks.next = &clock->callbacks;
  clock->callbacks.last = &clock->callbacks;
}

static void
RunFrameCallbacks (FrameClock *clock)
{
  FrameClockCallback *callback;

  callback = clock->callbacks.next;

  while (callback != &clock->callbacks)
    {
      callback->frame (clock, callback->data);
      callback = callback->next;
    }
}

static void
NoteFakeFrame (Timer *timer, void *data, struct timespec time)
{
  FrameClock *clock;

  clock = data;

  if (clock->in_frame
      && (clock->finished_frame_id == clock->next_frame_id))
    {
      clock->in_frame = False;
      RunFrameCallbacks (clock);
    }
}

void
XLFrameClockAfterFrame (FrameClock *clock,
			void (*frame_func) (FrameClock *, void *),
			void *data)
{
  FrameClockCallback *callback;

  callback = XLCalloc (1, sizeof *callback);

  callback->next = clock->callbacks.next;
  callback->last = &clock->callbacks;

  clock->callbacks.next->last = callback;
  clock->callbacks.next = callback;

  callback->data = data;
  callback->frame = frame_func;
}

void
XLFrameClockStartFrame (FrameClock *clock, Bool urgent)
{
  StartFrame (clock, urgent, True);
}

void
XLFrameClockEndFrame (FrameClock *clock)
{
  EndFrame (clock);
}

Bool
XLFrameClockFrameInProgress (FrameClock *clock)
{
  if (clock->frozen_until_end_frame)
    /* Don't consider a frame as being in progress, since the frame
       counter has been incremented to freeze the display.  */
    return False;

  return clock->in_frame;
}

/* N.B. that this function is called from popups, where normal
   freezing does not work, as the window manager does not
   cooperate.  */

void
XLFrameClockFreeze (FrameClock *clock)
{
  /* Start a frame now, unless one is already in progress, in which
     case it suffices to get rid of the timer.  */
  if (!clock->end_frame_timer)
    StartFrame (clock, False, False);
  else
    {
      RemoveTimer (clock->end_frame_timer);
      clock->end_frame_timer = NULL; 
    }

  /* Don't unfreeze until the next EndFrame.  */
  clock->frozen_until_end_frame = True;
  clock->frozen = True;
}

void
XLFrameClockHandleFrameEvent (FrameClock *clock, XEvent *event)
{
  uint64_t low, high, value;

  if (event->xclient.message_type == _NET_WM_FRAME_DRAWN)
    {
      /* Mask these values against 0xffffffff, since Xlib sign-extends
	 these 32 bit values to fit into long, which can be 64
	 bits.  */
      low = event->xclient.data.l[0] & 0xffffffff;
      high = event->xclient.data.l[1] & 0xffffffff;
      value = low | (high << 32);

      if (value == clock->finished_frame_id
	  && clock->in_frame
	  /* If this means the frame has been completely drawn, then
	     clear in_frame and run frame callbacks to i.e. draw any
	     late frame.  */
	  && (clock->finished_frame_id == clock->next_frame_id))
	{
	  /* Record the time at which the frame was drawn.  */
	  low = event->xclient.data.l[2] & 0xffffffff;
	  high = event->xclient.data.l[3] & 0xffffffff;

	  /* Actually compute the time and save it.  */
	  clock->last_frame_time = low | (high << 32);

	  /* Run any frame callbacks, since drawing has finished.  */
	  clock->in_frame = False;
	  RunFrameCallbacks (clock);
	}
    }

  if (event->xclient.message_type == _NET_WM_FRAME_TIMINGS)
    {
      /* Save the presentation time and refresh interval.  There is no
	 need to mask these values, since they are being put into
	 (u)int32_t.  */
      clock->presentation_time = event->xclient.data.l[2];
      clock->refresh_interval = event->xclient.data.l[3];

      if (clock->refresh_interval & (1U << 31))
	{
	  /* This means frame timing information is unavailable.  */
	  clock->presentation_time = 0;
	  clock->refresh_interval = 0;
	}
    }

  if (event->xclient.message_type == WM_PROTOCOLS
      && event->xclient.data.l[0] == _NET_WM_SYNC_REQUEST
      && event->xclient.data.l[4] == 1)
    {
      low = event->xclient.data.l[2];
      high = event->xclient.data.l[3];
      value = low | (high << 32);

      /* Ensure that value is even.  */
      if (value % 2)
	value += 1;

      /* The frame clock is now frozen, and we will have to wait for a
	 client to ack_configure and then commit something.  */

      if (clock->end_frame_timer)
	{
	  /* End the frame now, and clear in_frame early.  */
	  RemoveTimer (clock->end_frame_timer);
	  clock->end_frame_timer = NULL;
	  EndFrame (clock);

	  /* The reason for clearing in_frame is that otherwise a
	     future Commit after the configuration is acknowledged
	     will not be able to start a new frame and restart the
	     frame clock.  */
	  clock->in_frame = False;
	}

      clock->need_configure = True;
      clock->configure_id = value;
      clock->frozen = True;

      if (clock->freeze_callback)
	clock->freeze_callback (clock->freeze_callback_data);
    }
}

void
XLFreeFrameClock (FrameClock *clock)
{
  FreeFrameCallbacks (clock);

  if (frame_sync_supported)
    {
      XSyncDestroyCounter (compositor.display,
			   clock->primary_counter);
      XSyncDestroyCounter (compositor.display,
			   clock->secondary_counter);
    }
  else
    RemoveTimer (clock->static_frame_timer);

  if (clock->end_frame_timer)
    RemoveTimer (clock->end_frame_timer);

  XLFree (clock);
}

FrameClock *
XLMakeFrameClockForWindow (Window window)
{
  FrameClock *clock;
  XSyncValue initial_value;
  struct timespec default_refresh_rate;

  clock = XLCalloc (1, sizeof *clock);
  clock->next_frame_id = 0;

  XLOutputGetMinRefresh (&default_refresh_rate);

  XSyncIntToValue (&initial_value, 0);

  if (frame_sync_supported)
    {
      clock->primary_counter
	= XSyncCreateCounter (compositor.display,
			      initial_value);
      clock->secondary_counter
	= XSyncCreateCounter (compositor.display,
			      initial_value);
    }
  else
    clock->static_frame_timer
      = AddTimer (NoteFakeFrame, clock,
		  default_refresh_rate);

  /* Initialize sentinel link.  */
  clock->callbacks.next = &clock->callbacks;
  clock->callbacks.last = &clock->callbacks;

  if (frame_sync_supported)
    XChangeProperty (compositor.display, window,
		     _NET_WM_SYNC_REQUEST_COUNTER, XA_CARDINAL, 32,
		     PropModeReplace,
		     (unsigned char *) &clock->primary_counter, 2);

  if (getenv ("DEBUG_REFRESH_PREDICTION"))
    clock->predict_refresh = True;

  return clock;
}

void
XLFrameClockUnfreeze (FrameClock *clock)
{
  clock->frozen = False;
}

Bool
XLFrameClockNeedConfigure (FrameClock *clock)
{
  return clock->need_configure;
}

Bool
XLFrameClockSyncSupported (void)
{
  return frame_sync_supported;
}

Bool
XLFrameClockIsFrozen (FrameClock *clock)
{
  return clock->frozen;
}

Bool
XLFrameClockCanBatch (FrameClock *clock)
{
  /* Hmm... this doesn't seem very accurate.  Maybe it would be a
     better to test against the target presentation time instead.  */

  return clock->end_frame_timer != NULL;
}

void
XLFrameClockSetPredictRefresh (FrameClock *clock)
{
  /* This sets whether or not the frame clock should try to predict
     when the compositing manager will draw a frame to display.

     It is useful when multiple subsurfaces are trying to start
     subframes on the same toplevel at the same time; in that case,
     the subframes will be grouped into a single synchronized frame,
     instead of being postponed.  */

  if (compositor.server_time_monotonic)
    clock->predict_refresh = True;
}

void
XLFrameClockDisablePredictRefresh (FrameClock *clock)
{
  /* This sets whether or not the frame clock should try to predict
     when the compositing manager will draw a frame to display.

     It is useful when multiple subsurfaces are trying to start
     subframes on the same toplevel at the same time; in that case,
     the subframes will be grouped into a single synchronized frame,
     instead of being postponed.  */

  clock->predict_refresh = False;
}

void
XLFrameClockSetFreezeCallback (FrameClock *clock, void (*callback) (void *),
			       void *data)
{
  clock->freeze_callback = callback;
  clock->freeze_callback_data = data;
}


/* Cursor animation clock-related functions.  */

static void
NoteCursorFrame (Timer *timer, void *data, struct timespec time)
{
  CursorClockCallback *callback;

  callback = cursor_callbacks.next;

  while (callback != &cursor_callbacks)
    {
      callback->frame (callback->data, time);
      callback = callback->next;
    }
}

void *
XLAddCursorClockCallback (void (*frame_func) (void *, struct timespec),
			  void *data)
{
  CursorClockCallback *callback;

  callback = XLMalloc (sizeof *callback);

  callback->next = cursor_callbacks.next;
  callback->last = &cursor_callbacks;

  cursor_callbacks.next->last = callback;
  cursor_callbacks.next = callback;

  callback->frame = frame_func;
  callback->data = data;

  return callback;
}

void
XLStopCursorClockCallback (void *key)
{
  CursorClockCallback *callback;

  callback = key;

  /* First, make the list skip past CALLBACK.  */
  callback->last->next = callback->next;
  callback->next->last = callback->last;

  /* Then, free CALLBACK.  */
  XLFree (callback);
}

void
XLStartCursorClock (void)
{
  struct timespec cursor_refresh_rate;

  if (cursor_count++)
    return;

  cursor_refresh_rate.tv_sec = 0;
  cursor_refresh_rate.tv_nsec = 60000000;
  cursor_clock = AddTimer (NoteCursorFrame, NULL,
			   cursor_refresh_rate);
}

void
XLStopCursorClock (void)
{
  if (--cursor_count)
    return;

  RemoveTimer (cursor_clock);
  cursor_clock = NULL;
}

void
XLInitFrameClock (void)
{
  Bool supported;
  int xsync_event_base, xsync_error_base;

  supported = XSyncQueryExtension (compositor.display,
				   &xsync_event_base,
				   &xsync_error_base);

  if (supported)
    supported = XSyncInitialize (compositor.display,
				 &xsync_major, &xsync_minor);

  if (!supported)
    {
      fprintf (stderr, "A compatible version of the Xsync extension"
	       " was not found\n");
      exit (1);
    }

  if (!getenv ("DISABLE_FRAME_SYNCHRONIZATION"))
    frame_sync_supported = XLWmSupportsHint (_NET_WM_FRAME_DRAWN);

  /* Initialize cursor callbacks.  */
  cursor_callbacks.next = &cursor_callbacks;
  cursor_callbacks.last = &cursor_callbacks;
}