Merge branch 'issue43_unstablefps' into develop

Source/Examples/OpenTK/Test/GameWindowStates.cs

@@ -25,9 +25,23 @@ namespace Examples.Tests
         int texture;
         bool mouse_in_window = false;
         bool viewport_changed = true;
+
+        // time drift
         Stopwatch watch = new Stopwatch();
         double update_time, render_time;
 
+        // timing information
+        double timestamp;
+        int update_count;
+        int update_fps;
+        int render_count;
+        int render_fps;
+
+        // position of moving objects on screen
+        double variable_update_timestep_pos = -1;
+        double variable_refresh_timestep_pos = -1;
+        double fixed_update_timestep_pos = -1;
+
         public GameWindowStates()
             : base(800, 600, GraphicsMode.Default)
         {
@@ -35,10 +49,10 @@ namespace Examples.Tests
             Keyboard.KeyRepeat = true;
             KeyDown += KeyDownHandler;
             KeyPress += KeyPressHandler;
-            
+
             MouseEnter += delegate { mouse_in_window = true; };
             MouseLeave += delegate { mouse_in_window = false; };
-            
+
             Mouse.Move += MouseMoveHandler;
             Mouse.ButtonDown += MouseButtonHandler;
             Mouse.ButtonUp += MouseButtonHandler;
@@ -110,7 +124,7 @@ namespace Examples.Tests
         {
             return val > max ? max : val < min ? min : val;
         }
-        
+
         static float DrawString(Graphics gfx, string str, int line)
         {
             return DrawString(gfx, str, line, 0);
@@ -217,6 +231,8 @@ namespace Examples.Tests
         {
             double clock_time = watch.Elapsed.TotalSeconds;
             update_time += e.Time;
+            timestamp += e.Time;
+            update_count++;
 
             using (Graphics gfx = Graphics.FromImage(TextBitmap))
             {
@@ -247,22 +263,47 @@ namespace Examples.Tests
                 // Timing information
                 line++;
                 DrawString(gfx, "Timing:", line++);
-                DrawString(gfx, String.Format("Frequency: update ({0:f2}/{1:f2}); render ({2:f2}/{3:f2})",
+                DrawString(gfx,
-                    UpdateFrequency, TargetUpdateFrequency, RenderFrequency, TargetRenderFrequency), line++);
+                    String.Format("Frequency: update {4} ({0:f2}/{1:f2}); render {5} ({2:f2}/{3:f2})",
-                DrawString(gfx, String.Format("Period: update ({0:f4}/{1:f4}); render ({2:f4}/{3:f4})",
+                        UpdateFrequency, TargetUpdateFrequency,
-                    UpdatePeriod, TargetUpdatePeriod, RenderPeriod, TargetRenderPeriod), line++);
+                        RenderFrequency, TargetRenderFrequency,
+                        update_fps, render_fps),
+                    line++);
+                DrawString(gfx,
+                    String.Format("Period: update {4:N4} ({0:f4}/{1:f4}); render {5:N4} ({2:f4}/{3:f4})",
+                        UpdatePeriod, TargetUpdatePeriod,
+                        RenderPeriod, TargetRenderPeriod,
+                        1.0 / update_fps, 1.0 / render_fps),
+                    line++);
                 DrawString(gfx, String.Format("Time: update {0:f4}; render {1:f4}",
-                    UpdateTime, RenderTime), line++); 
+                    UpdateTime, RenderTime), line++);
                 DrawString(gfx, String.Format("Drift: clock {0:f4}; update {1:f4}; render {2:f4}",
                     clock_time, clock_time - update_time, clock_time - render_time), line++);
                 DrawString(gfx, String.Format("Text: {0}", TypedText.ToString()), line++);
 
+                if (timestamp >= 1)
+                {
+                    timestamp -= 1;
+                    update_fps = update_count;
+                    render_fps = render_count;
+                    update_count = 0;
+                    render_count = 0;
+
+                }
+
                 // Input information
                 line = DrawKeyboards(gfx, line);
                 line = DrawMice(gfx, line);
                 line = DrawJoysticks(gfx, line);
                 line = DrawLegacyJoysticks(gfx, Joysticks, line);
             }
+
+            fixed_update_timestep_pos += TargetUpdatePeriod;
+            variable_update_timestep_pos += e.Time;
+            if (fixed_update_timestep_pos >= 1)
+                fixed_update_timestep_pos -= 2;
+            if (variable_update_timestep_pos >= 1)
+                variable_update_timestep_pos -= 2;
         }
 
         int DrawJoysticks(Graphics gfx, int line)
@@ -323,7 +364,31 @@ namespace Examples.Tests
         protected override void OnRenderFrame(FrameEventArgs e)
         {
             render_time += e.Time;
+            render_count++;
 
+            GL.Clear(ClearBufferMask.ColorBufferBit);
+
+            if (viewport_changed)
+            {
+                viewport_changed = false;
+                GL.Viewport(0, 0, Width, Height);
+            }
+
+            DrawText();
+
+            DrawMovingObjects();
+
+            variable_refresh_timestep_pos += e.Time;
+            if (variable_refresh_timestep_pos >= 1)
+                variable_refresh_timestep_pos -= 2;
+
+            SwapBuffers();
+        }
+
+        // Uploads our text Bitmap to an OpenGL texture
+        // and displays is to screen.
+        private void DrawText()
+        {
             System.Drawing.Imaging.BitmapData data = TextBitmap.LockBits(
                 new System.Drawing.Rectangle(0, 0, TextBitmap.Width, TextBitmap.Height),
                 System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
@@ -331,29 +396,63 @@ namespace Examples.Tests
                 PixelType.UnsignedByte, data.Scan0);
             TextBitmap.UnlockBits(data);
 
-            if (viewport_changed)
+            Matrix4 text_projection = Matrix4.CreateOrthographicOffCenter(0, Width, Height, 0, -1, 1);
-            {
+            GL.MatrixMode(MatrixMode.Projection);
-                viewport_changed = false;
+            GL.LoadMatrix(ref text_projection);
-
+            GL.MatrixMode(MatrixMode.Modelview);
-                GL.Viewport(0, 0, Width, Height);
+            GL.LoadIdentity();
-
-                Matrix4 ortho_projection = Matrix4.CreateOrthographicOffCenter(0, Width, Height, 0, -1, 1);
-                GL.MatrixMode(MatrixMode.Projection);
-                GL.LoadMatrix(ref ortho_projection);
-            }
-
-            GL.Clear(ClearBufferMask.ColorBufferBit);
 
+            GL.Color4(Color4.White);
+            GL.Enable(EnableCap.Texture2D);
             GL.Begin(PrimitiveType.Quads);
-
             GL.TexCoord2(0, 0); GL.Vertex2(0, 0);
             GL.TexCoord2(1, 0); GL.Vertex2(TextBitmap.Width, 0);
             GL.TexCoord2(1, 1); GL.Vertex2(TextBitmap.Width, TextBitmap.Height);
             GL.TexCoord2(0, 1); GL.Vertex2(0, TextBitmap.Height);
-
             GL.End();
+            GL.Disable(EnableCap.Texture2D);
+        }
 
-            SwapBuffers();
+        // Draws three moving objects, using three different timing methods:
+        // 1. fixed framerate based on TargetUpdatePeriod
+        // 2. variable framerate based on UpdateFrame e.Time
+        // 3. variable framerate based on RenderFrame e.Time
+        // If the timing implementation is correct, all three objects
+        // should be moving at the same speed, regardless of the current
+        // UpdatePeriod and RenderPeriod.
+        void DrawMovingObjects()
+        {
+            Matrix4 thing_projection = Matrix4.CreateOrthographic(2, 2, -1, 1);
+            GL.MatrixMode(MatrixMode.Projection);
+            GL.LoadMatrix(ref thing_projection);
+
+            GL.MatrixMode(MatrixMode.Modelview);
+            GL.LoadIdentity();
+            GL.Translate(fixed_update_timestep_pos, -0.2, 0);
+            GL.Color4(Color4.Red);
+            DrawRectangle();
+
+            GL.MatrixMode(MatrixMode.Modelview);
+            GL.LoadIdentity();
+            GL.Translate(variable_update_timestep_pos, -0.4, 0);
+            GL.Color4(Color4.DarkGoldenrod);
+            DrawRectangle();
+
+            GL.MatrixMode(MatrixMode.Modelview);
+            GL.LoadIdentity();
+            GL.Translate(variable_refresh_timestep_pos, -0.8, 0);
+            GL.Color4(Color4.DarkGreen);
+            DrawRectangle();
+        }
+
+        private void DrawRectangle()
+        {
+            GL.Begin(PrimitiveType.Quads);
+            GL.Vertex2(-0.05, -0.05);
+            GL.Vertex2(+0.05, -0.05);
+            GL.Vertex2(+0.05, +0.05);
+            GL.Vertex2(-0.05, +0.05);
+            GL.End();
         }
 
         public static void Main()

Source/OpenTK/GameWindow.cs

@@ -75,6 +75,8 @@ namespace OpenTK
     {
         #region --- Fields ---
 
+        const double MaxFrequency = 500.0; // Frequency cap for Update/RenderFrame events
+
         readonly Stopwatch watch = new Stopwatch();
 
         IGraphicsContext glContext;
@@ -90,6 +92,10 @@ namespace OpenTK
         double update_timestamp; // timestamp of last UpdateFrame event
         double render_timestamp; // timestamp of last RenderFrame event
 
+        double update_epsilon; // quantization error for UpdateFrame events
+
+        bool is_running_slowly; // true, when UpdatePeriod cannot reach TargetUpdatePeriod
+
         VSyncMode vsync;
 
         FrameEventArgs update_args = new FrameEventArgs();
@@ -431,63 +437,84 @@ namespace OpenTK
             }
         }
 
+        double ClampElapsed(double elapsed)
+        {
+            return MathHelper.Clamp(elapsed, 0.0, 1.0);
+        }
+
         void DispatchUpdateAndRenderFrame(object sender, EventArgs e)
         {
-            const int max_frameskip = 10;
+            int is_running_slowly_retries = 4;
-            int frameskip = 0;
             double timestamp = watch.Elapsed.TotalSeconds;
+            double elapsed = 0;
 
-            do
+            elapsed = ClampElapsed(timestamp - update_timestamp);
+            while (elapsed > 0 && elapsed + update_epsilon >= TargetUpdatePeriod)
             {
-                // Raise UpdateFrame events until we catch up with our target update rate.
+                RaiseUpdateFrame(elapsed, ref timestamp);
-                double update_elapsed = MathHelper.Clamp(timestamp - update_timestamp, 0.0, 1.0);
+                
-                if (RaiseUpdateFrame(update_elapsed))
+                // Calculate difference (positive or negative) between
+                // actual elapsed time and target elapsed time. We must
+                // compensate for this difference.
+                update_epsilon += elapsed - TargetUpdatePeriod;
+
+                // Prepare for next loop
+                elapsed = ClampElapsed(timestamp - update_timestamp);
+
+                if (TargetUpdatePeriod <= Double.Epsilon)
                 {
-                    update_period = update_elapsed;
+                    // According to the TargetUpdatePeriod documentation,
-                    update_timestamp = timestamp;
+                    // a TargetUpdatePeriod of zero means we will raise
-                    timestamp = watch.Elapsed.TotalSeconds;
+                    // UpdateFrame events as fast as possible (one event
-                    update_time = timestamp - update_timestamp;
+                    // per ProcessEvents() call)
-                }
-                else
-                {
-                    // We have executed enough UpdateFrame events to catch up.
-                    // Break and issue a RenderFrame event.
                     break;
                 }
-            } while (++frameskip < max_frameskip);
 
+                is_running_slowly = update_epsilon >= TargetUpdatePeriod;
+                if (is_running_slowly && --is_running_slowly_retries == 0)
+                {
+                    // If UpdateFrame consistently takes longer than TargetUpdateFrame
+                    // stop raising events to avoid hanging inside the UpdateFrame loop.
+                    break;
+                }
+            }
+
+            elapsed = ClampElapsed(timestamp - render_timestamp);
+            if (elapsed > 0 && elapsed >= TargetRenderPeriod)
+            {
+                RaiseRenderFrame(elapsed, ref timestamp);
+            }
+        }
+
+        void RaiseUpdateFrame(double elapsed, ref double timestamp)
+        {
+            // Raise UpdateFrame event
+            update_args.Time = elapsed;
+            OnUpdateFrameInternal(update_args);
+
+            // Update UpdatePeriod/UpdateFrequency properties
+            update_period = elapsed;
+
+            // Update UpdateTime property
+            update_timestamp = timestamp;
             timestamp = watch.Elapsed.TotalSeconds;
-            double render_elapsed = MathHelper.Clamp(timestamp - render_timestamp, 0.0, 1.0);
+            update_time = timestamp - update_timestamp;
-            if (RaiseRenderFrame(render_elapsed))
-            {
-                render_period = render_elapsed;
-                render_timestamp = timestamp;
-                timestamp = watch.Elapsed.TotalSeconds;
-                render_time = timestamp - render_timestamp;
-            }
-        }
-
-        bool RaiseUpdateFrame(double time)
-        {
-            if (time > 0 && time >= TargetUpdatePeriod)
-            {
-                update_args.Time = time;
-                OnUpdateFrameInternal(update_args);
-                return true;
-            }
-            return false;
         }
 
 
-        bool RaiseRenderFrame(double time)
+        void RaiseRenderFrame(double elapsed, ref double timestamp)
         {
-            if (time > 0 && time >= TargetRenderPeriod)
+            // Raise RenderFrame event
-            {
+            render_args.Time = elapsed;
-                render_args.Time = time;
+            OnRenderFrameInternal(render_args);
-                OnRenderFrameInternal(render_args);
+
-                return true;
+            // Update RenderPeriod/UpdateFrequency properties
-            }
+            render_period = elapsed;
-            return false;
+
+            // Update RenderTime property
+            render_timestamp = timestamp;
+            timestamp = watch.Elapsed.TotalSeconds;
+            render_time = timestamp - render_timestamp;
         }
 
         #endregion
@@ -656,7 +683,7 @@ namespace OpenTK
         /// </summary>
         /// <remarks>
         /// <para>A value of 0.0 indicates that RenderFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
-        /// <para>Values lower than 1.0Hz are clamped to 1.0Hz. Values higher than 200.0Hz are clamped to 200.0Hz.</para>
+        /// <para>Values lower than 1.0Hz are clamped to 0.0. Values higher than 500.0Hz are clamped to 200.0Hz.</para>
         /// </remarks>
         public double TargetRenderFrequency
         {
@@ -674,11 +701,11 @@ namespace OpenTK
                 {
                     TargetRenderPeriod = 0.0;
                 }
-                else if (value <= 200.0)
+                else if (value <= MaxFrequency)
                 {
                     TargetRenderPeriod = 1.0 / value;
                 }
-                else Debug.Print("Target render frequency clamped to 200.0Hz."); // TODO: Where is it actually performed?
+                else Debug.Print("Target render frequency clamped to {0}Hz.", MaxFrequency);
             }
         }
 
@@ -691,7 +718,7 @@ namespace OpenTK
         /// </summary>
         /// <remarks>
         /// <para>A value of 0.0 indicates that RenderFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
-        /// <para>Values lower than 0.005 seconds (200Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
+        /// <para>Values lower than 0.002 seconds (500Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
         /// </remarks>
         public double TargetRenderPeriod
         {
@@ -703,7 +730,7 @@ namespace OpenTK
             set
             {
                 EnsureUndisposed();
-                if (value <= 0.005)
+                if (value <= 1 / MaxFrequency)
                 {
                     target_render_period = 0.0;
                 }
@@ -724,7 +751,7 @@ namespace OpenTK
         /// </summary>
         /// <remarks>
         /// <para>A value of 0.0 indicates that UpdateFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
-        /// <para>Values lower than 1.0Hz are clamped to 1.0Hz. Values higher than 200.0Hz are clamped to 200.0Hz.</para>
+        /// <para>Values lower than 1.0Hz are clamped to 0.0. Values higher than 500.0Hz are clamped to 500.0Hz.</para>
         /// </remarks>
         public double TargetUpdateFrequency
         {
@@ -742,11 +769,11 @@ namespace OpenTK
                 {
                     TargetUpdatePeriod = 0.0;
                 }
-                else if (value <= 200.0)
+                else if (value <= MaxFrequency)
                 {
                     TargetUpdatePeriod = 1.0 / value;
                 }
-                else Debug.Print("Target update frequency clamped to 200.0Hz."); // TODO: Where is it actually performed?
+                else Debug.Print("Target render frequency clamped to {0}Hz.", MaxFrequency);
             }
         }
 
@@ -759,7 +786,7 @@ namespace OpenTK
         /// </summary>
         /// <remarks>
         /// <para>A value of 0.0 indicates that UpdateFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
-        /// <para>Values lower than 0.005 seconds (200Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
+        /// <para>Values lower than 0.002 seconds (500Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
         /// </remarks>
         public double TargetUpdatePeriod
         {
@@ -771,7 +798,7 @@ namespace OpenTK
             set
             {
                 EnsureUndisposed();
-                if (value <= 0.005)
+                if (value <= 1 / MaxFrequency)
                 {
                     target_update_period = 0.0;
                 }
@@ -779,7 +806,7 @@ namespace OpenTK
                 {
                     target_update_period = value;
                 }
-                else Debug.Print("Target update period clamped to 1.0 seconds."); // TODO: Where is it actually performed?
+                else Debug.Print("Target update period clamped to 1.0 seconds.");
             }
         }