[client] ds: waitFrame now returns a bool to force rendering if needed

X11 needs to calibrate to get the best possible latency, as such it
needs the scene to render so that the render time of the scene can be
accounted for in the delay calculation.

client/displayservers/Wayland/window.c

@@ -138,13 +138,15 @@ static const struct wl_callback_listener frame_listener = {
    .done = frameHandler,
 };
 
-void waylandWaitFrame(void)
+bool waylandWaitFrame(void)
 {
   lgWaitEvent(wlWm.frameEvent, TIMEOUT_INFINITE);
 
   struct wl_callback * callback = wl_surface_frame(wlWm.surface);
   if (callback)
     wl_callback_add_listener(callback, &frame_listener, NULL);
+
+  return false;
 }
 
 void waylandSkipFrame(void)

client/displayservers/X11/x11.c

@@ -1128,7 +1128,7 @@ static void x11GLSwapBuffers(void)
 }
 #endif
 
-static void x11WaitFrame(void)
+static bool x11WaitFrame(void)
 {
   /* wait until we are woken up by the present event */
   lgWaitEvent(x11.frameEvent, TIMEOUT_INFINITE);
@@ -1196,6 +1196,13 @@ static void x11WaitFrame(void)
 
   struct timespec ts = { .tv_nsec = delay * 1000 };
   while(nanosleep(&ts, &ts)) {};
+
+  /* force rendering until we have finished calibration so we can take into
+   * account how long it takes for the scene to render */
+  if (calibrate < CALIBRATION_COUNT)
+    return true;
+
+  return false;
 }
 
 static void x11StopWaitFrame(void)

client/include/interface/displayserver.h

@@ -154,8 +154,11 @@ struct LG_DisplayServerOps
 #endif
 
   /* Waits for a good time to render the next frame in time for the next vblank.
-   * This is optional and a display server may choose to not implement it. */
-  void (*waitFrame)(void);
+   * This is optional and a display server may choose to not implement it.
+   *
+   * return true to force the frame to be rendered, this is used by X11 for
+   * calibration */
+  bool (*waitFrame)(void);
 
   /* This must be called when waitFrame returns, but no frame is actually rendered. */
   void (*skipFrame)(void);

client/src/main.c

@@ -171,14 +171,17 @@ static int renderThread(void * unused)
 
   while(g_state.state != APP_STATE_SHUTDOWN)
   {
+    bool forceRender = false;
+    if (g_state.jitRender)
+      forceRender = g_state.ds->waitFrame();
+
     app_handleRenderEvent(microtime());
     if (g_state.jitRender)
     {
-      g_state.ds->waitFrame();
-
       const uint64_t pending =
         atomic_load_explicit(&g_state.pendingCount, memory_order_acquire);
       if (!lgResetEvent(g_state.frameEvent)
+          && !forceRender
           && !pending
           && !app_overlayNeedsRender()
           && !g_state.lgr->needs_render(g_state.lgrData))