public override TKChartData GetPoint(TKChart chart, nuint dataIndex, nuint seriesIndex)
 {
     TKChartDataPoint point = new TKChartDataPoint ();
     point.DataXValue = new NSNumber (dataIndex);
     point.DataYValue = new NSNumber(r.Next (100));
     return point;
 }

 public override void RequestTile(nuint x, nuint y, nuint zoom, ITileReceiver receiver)
 {
     _tileImageAsync((int)x, (int)y, (int)zoom).ContinueWith((Task<byte[]> task) =>
     {
         var imgByte = task.Result;
         var image = new UIImage(NSData.FromArray(imgByte));
         receiver.ReceiveTile(x, y, zoom, image);
     });
 }

			public override TKChartPointLabel LabelForDataPoint (TKChart chart, TKChartData dataPoint, string propertyName, TKChartSeries series, nuint dataIndex)
			{
				TKChartDataPoint point = (TKChartDataPoint)dataPoint;
				if (series.Index == (nuint)this.selectedSeriesIndex && dataIndex == (nuint)this.selectedDataPointIndex) {
					return new MyPointLabel (point, series, String.Format ("{0}", point.DataYValue));
				}

				
				return new TKChartPointLabel (point, series, String.Format ("{0}", point.DataYValue));
			}

            public override TKChartPaletteItem PaletteItemForPoint(TKChart chart, nuint index, TKChartSeries series)
            {
                if (series.Index == (nuint)this.selectedSeriesIndex && index == (nuint)this.selectedDataPointIndex) {
                    return new TKChartPaletteItem (new TKStroke (UIColor.Black, (float)2.0), new TKSolidFill (UIColor.White));
                }

                if (series.Index == 0) {
                    return new TKChartPaletteItem (new TKSolidFill (new UIColor ((float)(108 / 255.0), (float)(181 / 255.0), (float)(250 / 255.0), (float)1.0)));
                }

                return new TKChartPaletteItem (new TKSolidFill (new UIColor ((float)(241 / 255.0), (float)(140 / 255.0), (float)(133 / 255.0), (float)1.0)));
            }

		public override CGRect CellFrameForTextContainer (NSTextContainer textContainer, CGRect lineFrag, CGPoint position, nuint charIndex)
		{
			var rect = base.CellFrameForTextContainer (textContainer, lineFrag, position, charIndex);

			return new CGRect (
				rect.Location,
				new CGSize (
					rect.Width + padding * 2,
					rect.Height + padding * 2
				)
			);
		}

            public override TKChartSeries GetSeries(TKChart chart, nuint index)
            {
                TKChartSeries series = null;

                if (index == 2) {
                    series = new TKChartSplineSeries ();
                } else {
                    series = new TKChartLineSeries ();
                }

                series.SelectionMode = TKChartSeriesSelectionMode.Series;
                series.Style.PointShape = new TKPredefinedShape (TKShapeType.Circle, new System.Drawing.SizeF (10, 10));
                series.Title = string.Format ("Series: {0}", index + 1);
                return series;
            }

		public override nint Read (IntPtr buffer, nuint len)
		{
			int actual = Math.Min ((int) len, (int) (total_length - read_length));

			byte [] bytes = new byte [actual];
			for (int i = 0; i < actual; i++)
				bytes [i] = (byte) 'z';

			read_length += actual;

			Marshal.Copy (bytes, 0, buffer, actual);

			if (actual == 0)
				Notify (CFStreamEventType.EndEncountered);

			return actual;
		}

		public override TKChartPointLabel LabelForDataPoint (TKChartData dataPoint, TKChartSeries series, nuint dataIndex)
		{
			TKChartDataPoint point = (TKChartDataPoint)dataPoint;
			if (series.Index == (nuint)this.SelectedSeries && dataIndex == (nuint)this.SelectedDataPoint) {
				if (this.labelLayer == null) {
					this.labelLayer = new SelectedPointLabel ();
				}

				this.labelLayer.LabelStyle = series.Style.PointLabelStyle;
				this.labelLayer.Text = String.Format ("{0}", point.DataYValue);
				this.isSelectedPoint = true;
				return null;
			}

			this.isSelectedPoint = false;
			return new TKChartPointLabel (dataPoint, series, String.Format ("{0}", point.DataYValue));
		}

			public override void DidDisplayPhoto (PhotoBrowser photoBrowser, nuint index)
			{
				Console.WriteLine ("Did start viewing photo at index {0}.", index);
			}

			public override void OnSelectedChanged (PhotoBrowser photoBrowser, nuint index, bool selected)
			{
				_selections [index] = selected;
				Console.WriteLine ("Photo at index {0} selected ? {1}.", index, selected);
			}

			public override bool IsPhotoSelected (PhotoBrowser photoBrowser, nuint index)
			{
				return _selections [index];
			}

			public override IPhoto GetThumbnail (PhotoBrowser photoBrowser, nuint index)
			{
				return thumbs [(int)index];
			}

			public override IPhoto GetPhoto (PhotoBrowser photoBrowser, nuint index)
			{
				return photos [(int)index];
			}

		void RenderBox (IMTLRenderCommandEncoder renderEncoder, GameView view, nuint offset, string name)
		{
			renderEncoder.PushDebugGroup (name);
			//  set context state
			renderEncoder.SetRenderPipelineState (pipelineState);
			renderEncoder.SetVertexBuffer (vertexBuffer, 0, 0);
			renderEncoder.SetVertexBuffer (dynamicConstantBuffer [constantDataBufferIndex], offset, 1);

			// tell the render context we want to draw our primitives
			renderEncoder.DrawPrimitives (MTLPrimitiveType.Triangle, 0, 36, 1);
			renderEncoder.PopDebugGroup ();
		}

 public override void GetTimelineEntriesBeforeDate(CLKComplication complication, NSDate beforeDate, nuint limit, Action<CLKComplicationTimelineEntry[]> entries)
 {
     Console.WriteLine ("GetTimelineEntriesBeforeDate");
     entries (null);
 }

        public override void ViewDidLoad()
        {
            colors = NSArray.FromNSObjects (UIColor.Red, UIColor.Orange, UIColor.Yellow,
                                            UIColor.Green, UIColor.Blue, UIColor.Purple);

            View.BackgroundColor = colors.GetItem<UIColor> (colorIndex);
            colorIndex = (colorIndex + 1) % colors.Count;
        }

		// Designated initializer
		public Quad (IMTLDevice device)
		{
			if (device == null)
				throw new Exception ("ERROR: Invalid device!");

			vertexBuffer = device.CreateBuffer<Vector4> (quadVertices, MTLResourceOptions.CpuCacheModeDefault);
			if (vertexBuffer == null)
				Console.WriteLine ("ERROR: Failed creating a vertex buffer for a quad!");
			vertexBuffer.Label = "quad vertices";

			texCoordBuffer = device.CreateBuffer<Vector2> (quadTexCoords, MTLResourceOptions.CpuCacheModeDefault);
			if (texCoordBuffer == null)
				Console.WriteLine ("ERROR: Failed creating a 2d texture coordinate buffer!");
			texCoordBuffer.Label = "quad texcoords";

			vertexIndex = 0;
			texCoordIndex = 1;
			Aspect = 1f;

			scale = Vector2.One;
		}

		public Renderer ()
		{
			// initialize properties
			sampleCount = 1;
			depthPixelFormat = MTLPixelFormat.Depth32Float;
			stencilPixelFormat = MTLPixelFormat.Invalid;

			// find a usable Device
			device = MTLDevice.SystemDefault;

			// create a new command queue
			commandQueue = device.CreateCommandQueue ();

			NSError error;
			shaderLibrary = device.CreateLibrary ("default.metallib", out error);

			// if the shader libary isnt loading, nothing good will happen
			if (shaderLibrary == null)
				throw new Exception ("ERROR: Couldnt create a default shader library");

			inflightSemaphore = new Semaphore (maxInflightBuffers, maxInflightBuffers);
		}

		public Renderer ()
		{
			sampleCount = 4;
			depthPixelFormat = MTLPixelFormat.Depth32Float;
			stencilPixelFormat = MTLPixelFormat.Invalid;

			// find a usable Device
			device = MTLDevice.SystemDefault;

			// create a new command queue
			commandQueue = device.CreateCommandQueue ();

			NSError error;
			defaultLibrary = device.CreateLibrary ("default.metallib", out error);

			// if the shader libary isnt loading, nothing good will happen
			if (defaultLibrary == null)
				throw new Exception ("ERROR: Couldnt create a default shader library");

			constantDataBufferIndex = 0;
			inflightSemaphore = new Semaphore (max_inflight_buffers, max_inflight_buffers);

			constantBuffer = new Uniforms[2];
			constantBuffer [0].ambientColor = box1AmbientColor;
			constantBuffer [0].diffuseColor = box1DiffuseColor;

			constantBuffer [1].ambientColor = box2AmbientColor;
			constantBuffer [1].diffuseColor = box2DiffuseColor;

			multiplier = 1;
		}