Interrupt GPU command processing when a frame's fence is reached. (#1741)

* Interrupt GPU command processing when a frame's fence is reached.

* Accumulate times rather than %s

* Accurate timer for vsync

Spin wait for the last .667ms of a frame. Avoids issues caused by signalling 16ms vsync. (periodic stutters in smo)

* Use event wait for better timing.

* Fix lazy wait

Windows doesn't seem to want to do 1ms consistently, so force a spin if we're less than 2ms.

* A bit more efficiency on frame waits.

Should now wait the remainder 0.6667 instead of 1.6667 sometimes (odd waits above 1ms are reliable, unlike 1ms waits)

* Better swap interval 0 solution

737 fps without breaking a sweat. Downside: Vsync can no longer be disabled on games that use the event heavily (link's awakening - which is ok since it breaks anyways)

* Fix comment.

* Address Comments.

Ryujinx.Graphics.Gpu/Window.cs

@@ -2,6 +2,7 @@ using Ryujinx.Graphics.GAL;
 using Ryujinx.Graphics.Gpu.Image;
 using System;
 using System.Collections.Concurrent;
+using System.Threading;
 
 namespace Ryujinx.Graphics.Gpu
 {
@@ -69,6 +70,8 @@ namespace Ryujinx.Graphics.Gpu
 
         private readonly ConcurrentQueue<PresentationTexture> _frameQueue;
 
+        private int _framesAvailable;
+
         /// <summary>
         /// Creates a new instance of the GPU presentation window.
         /// </summary>
@@ -157,5 +160,29 @@ namespace Ryujinx.Graphics.Gpu
                 pt.ReleaseCallback(pt.UserObj);
             }
         }
+
+        /// <summary>
+        /// Indicate that a frame on the queue is ready to be acquired.
+        /// </summary>
+        public void SignalFrameReady()
+        {
+            Interlocked.Increment(ref _framesAvailable);
+        }
+
+        /// <summary>
+        /// Determine if any frames are available, and decrement the available count if there are.
+        /// </summary>
+        /// <returns>True if a frame is available, false otherwise</returns>
+        public bool ConsumeFrameAvailable()
+        {
+            if (Interlocked.CompareExchange(ref _framesAvailable, 0, 0) != 0)
+            {
+                Interlocked.Decrement(ref _framesAvailable);
+
+                return true;
+            }
+
+            return false;
+        }
     }
 }