C# CGGradient类代码示例

        //Generated with PaintCode 2.2
        public override void Draw(CGRect rect)
        {
            base.Draw(rect);

            // General Declarations
            var colorSpace = CGColorSpace.CreateDeviceRGB();
            var context = UIGraphics.GetCurrentContext();

            // Color Declarations
            var darkBlue = UIColor.FromRGBA(0.053f, 0.123f, 0.198f, 1.000f);
            var lightBlue = UIColor.FromRGBA(0.191f, 0.619f, 0.845f, 1.000f);

            // Gradient Declarations
            var backgroundGradientColors = new CGColor [] {lightBlue.CGColor, darkBlue.CGColor};
            var backgroundGradientLocations = new nfloat [] {0.0f, 1.0f};
            var backgroundGradient = new CGGradient(colorSpace, backgroundGradientColors, backgroundGradientLocations);

            // Rectangle Drawing
            var rectangleRect = new CGRect(rect.GetMinX() + (float)Math.Floor(rect.Width * -0.12917f + 0.5f), rect.GetMinY() + (float)Math.Floor(rect.Height * 0.00000f + 0.5f), (float)Math.Floor(rect.Width * 1.00000f + 0.5f) - (float)Math.Floor(rect.Width * -0.12917f + 0.5f), (float)Math.Floor(rect.Height * 1.00000f + 0.5f) - (float)Math.Floor(rect.Height * 0.00000f + 0.5f));
            var rectanglePath = UIBezierPath.FromRect(rectangleRect);
            context.SaveState();
            rectanglePath.AddClip();
            context.DrawLinearGradient(backgroundGradient,
                new PointF((float)rectangleRect.GetMidX(), (float)rectangleRect.GetMinY()),
                new PointF((float)rectangleRect.GetMidX(), (float)rectangleRect.GetMaxY()),
                0);
            context.RestoreState();
        }

        void Renderer_Element_SizeChanged(object sender, EventArgs e)
        {
            var element = sender as GradientView;
            if (element == null)
                return;
            
            var bounds = element.Bounds;
            var rect = new CGRect(bounds.X, bounds.Y, bounds.Width, bounds.Height);

            UIGraphics.BeginImageContext(rect.Size);
            using (CGContext g = UIGraphics.GetCurrentContext())
            {
                using (var rgb = CGColorSpace.CreateDeviceRGB())
                {
                    nfloat[] colors = GetFloatArrayFromColors(element.StartColor, element.EndColor);

                    var gradient = new CGGradient(rgb, colors, null);

                    g.DrawRadialGradient(gradient, new CGPoint(0, 0), new nfloat(0), new CGPoint(100, 100), new nfloat(1000), CGGradientDrawingOptions.None);
                }


                using (var im = UIGraphics.GetImageFromCurrentImageContext())
                using (var imageHolder = new UIImageView(im))
                    Container.AddSubview(imageHolder);
                UIGraphics.EndImageContext();
            }

        }

        public static UIImage MakeBlueSea()
        {
            UIGraphics.BeginImageContext(new System.Drawing.SizeF(640,1136));
            //BEGIN PAINTCODE

            //// General Declarations
            var colorSpace = CGColorSpace.CreateDeviceRGB();
            var context = UIGraphics.GetCurrentContext();

            //// Color Declarations
            UIColor color = UIColor.FromRGBA(0.114f, 0.705f, 1.000f, 1.000f);
            UIColor gradientColor = UIColor.FromRGBA(0.088f, 0.606f, 0.676f, 1.000f);
            UIColor gradientColor2 = UIColor.FromRGBA(0.018f, 0.509f, 0.675f, 1.000f);

            //// Gradient Declarations
            var gradientColors = new CGColor [] {color.CGColor, UIColor.FromRGBA(0.066f, 0.607f, 0.837f, 1.000f).CGColor, gradientColor2.CGColor, gradientColor.CGColor};
            var gradientLocations = new float [] {0, 0.21f, 0.46f, 1};
            var gradient = new CGGradient(colorSpace, gradientColors, gradientLocations);

            //// Rectangle Drawing
            var rectanglePath = UIBezierPath.FromRect(new RectangleF(-46.5f, -35.5f, 728, 1192));
            context.SaveState();
            rectanglePath.AddClip();
            context.DrawLinearGradient(gradient, new PointF(317.5f, -35.5f), new PointF(317.5f, 1156.5f), 0);
            context.RestoreState();
            UIColor.Black.SetStroke();
            rectanglePath.LineWidth = 1;
            rectanglePath.Stroke();

            //END PAINTCODE

            var converted = UIGraphics.GetImageFromCurrentImageContext ();
            UIGraphics.EndImageContext ();
            return converted;
        }

		static MessageSummaryView ()
		{
			using (var colorspace = CGColorSpace.CreateDeviceRGB ())
			{
				gradient = new CGGradient (colorspace, new float [] { /* first */ .52f, .69f, .96f, 1, /* second */ .12f, .31f, .67f, 1 }, null); //new float [] { 0, 1 });
			}
		}

        public override void Draw(CGRect rect)
        {
            using (CGContext context = UIGraphics.GetCurrentContext())
            {
                switch (_Style)
                {
                    case SIAlertViewBackgroundStyle.Gradient:
                        {
                            nfloat[] locations = { 0.0f, 1.0f };
                            nfloat[] colors = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.75f };
                            CGGradient gradient = new CGGradient(CGColorSpace.CreateDeviceRGB(), colors, locations);

                            CGPoint center = new CGPoint(Bounds.Size.Width / 2, Bounds.Size.Height / 2);
                            nfloat radius = (nfloat)Math.Min(Bounds.Size.Width, Bounds.Size.Height);
                            context.DrawRadialGradient(gradient, center, 0, center, radius, CGGradientDrawingOptions.DrawsAfterEndLocation);
                            break;
                        }
                    case SIAlertViewBackgroundStyle.Solid:
                        {
                            UIColor.FromWhiteAlpha(0f, 0.5f).SetColor();
                            context.SetFillColor(UIColor.FromWhiteAlpha(0f, 0.5f).CGColor);
                            context.FillRect(Bounds);
                            break;
                        }
                }
            }
        }

 private void SetUp()
 {
     CGColorSpace colorSpace = CGColorSpace.CreateDeviceRGB ();
     gradient = new CGGradient (
         colorSpace,
         new float[] { 0.95f, 0.95f, 0.95f, 1,
                       0.85f, 0.85f, 0.85f, 1},
         new float[] { 0, 1 });
 }

		public GradientTheme()
		{
			//BackgroundColor = UIColor.Clear;
			TextColor = UIColor.Black;
			TextShadowColor = UIColor.LightGray;
			TextShadowOffset = new SizeF(1, 0);
			
			gradient = new CGGradient(CGColorSpace.CreateDeviceRGB(), new float[] { 0.95f, 0.95f, 0.95f, 1, 0.85f, 0.85f, 0.85f, 1 }, new float[] { 0, 1 });
		}

        public static UIImage AddImageReflection(UIImage image, float reflectionFraction)
        {
            int reflectionHeight = (int) (image.Size.Height * reflectionFraction);

            // Create a 2 bit CGImage containing a gradient that will be used for masking the
            // main view content to create the 'fade' of the reflection.  The CGImageCreateWithMask
            // function will stretch the bitmap image as required, so we can create a 1 pixel wide gradient

            // gradient is always black and white and the mask must be in the gray colorspace
            var colorSpace = CGColorSpace.CreateDeviceGray ();

            // Creat the bitmap context
            var gradientBitmapContext = new CGBitmapContext (IntPtr.Zero, 1, reflectionHeight, 8, 0, colorSpace, CGImageAlphaInfo.None);

            // define the start and end grayscale values (with the alpha, even though
            // our bitmap context doesn't support alpha the gradien requires it)
            float [] colors = { 0, 1, 1, 1 };

            // Create the CGGradient and then release the gray color space
            var grayScaleGradient = new CGGradient (colorSpace, colors, null);
            colorSpace.Dispose ();

            // create the start and end points for the gradient vector (straight down)
            var gradientStartPoint = new PointF (0, reflectionHeight);
            var gradientEndPoint = PointF.Empty;

            // draw the gradient into the gray bitmap context
            gradientBitmapContext.DrawLinearGradient (grayScaleGradient, gradientStartPoint,
                                                      gradientEndPoint, CGGradientDrawingOptions.DrawsAfterEndLocation);
            grayScaleGradient.Dispose ();

            // Add a black fill with 50% opactiy
            gradientBitmapContext.SetGrayFillColor (0, 0.5f);
            gradientBitmapContext.FillRect (new RectangleF (0, 0, 1, reflectionHeight));

            // conver the context into a CGImage and release the context
            var gradientImageMask = gradientBitmapContext.ToImage ();
            gradientBitmapContext.Dispose ();

            // create an image by masking the bitmap of the mainView content with the gradient view
            // then release the pre-masked content bitmap and the gradient bitmap
            var reflectionImage = image.CGImage.WithMask (gradientImageMask);
            gradientImageMask.Dispose ();

            var size = new SizeF (image.Size.Width, image.Size.Height + reflectionHeight);

            UIGraphics.BeginImageContext (size);
            image.Draw (PointF.Empty);
            var context = UIGraphics.GetCurrentContext ();
            context.DrawImage (new RectangleF (0, image.Size.Height, image.Size.Width, reflectionHeight), reflectionImage);

            var result = UIGraphics.GetImageFromCurrentImageContext ();
            UIGraphics.EndImageContext ();
            reflectionImage.Dispose ();

            return result;
        }

		public MovieElement(string caption) : base(UITableViewCellStyle.Default)
		{
			Caption = caption;
			CGColorSpace colorSpace = CGColorSpace.CreateDeviceRGB();
			gradient = new CGGradient(
			    colorSpace,
			    new float[] { 0.95f, 0.95f, 0.95f, 1, 
							  0.85f, 0.85f, 0.85f, 1},
				new float[] { 0, 1 } );
		}

 static HeaderView()
 {
     using (var rgb = CGColorSpace.CreateDeviceRGB()){
         float [] colorsBottom = {
             1, 1, 1, 1f,
             0.97f, 0.97f, 0.97f, 1f
         };
         Gradient = new CGGradient (rgb, colorsBottom, null);
     }
 }

        public override void DrawInContext(CoreGraphics.CGContext ctx)
        {
            base.DrawInContext (ctx);

            var knobFrame = CGRect.Inflate(PaintFrame, -2.0f, -2.0f);

            UIBezierPath knobPath = UIBezierPath.FromRoundedRect((CGRect)knobFrame, (nfloat)knobFrame.Height * Slider.Curvaceousness / 2.0f);

            // 1) fill - with a subtle shadow
            ctx.SetShadow(new CGSize(0, 1), 1.0f, UIColor.Gray.CGColor);
            ctx.SetFillColor( Slider.KnobColor.CGColor);
            ctx.AddPath( knobPath.CGPath);
            ctx.FillPath ();

            // 2) outline
            ctx.SetStrokeColor(UIColor.Gray.CGColor);
            ctx.SetLineWidth((nfloat)0.5f);
            ctx.AddPath(knobPath.CGPath);
            ctx.StrokePath ();

            // 3) inner gradient
            var rect = CGRect.Inflate(knobFrame, -2.0f, -2.0f);
            var clipPath = UIBezierPath.FromRoundedRect ((CGRect)rect, (nfloat)rect.Height * Slider.Curvaceousness / 2.0f);

            CGGradient myGradient;
            CGColorSpace myColorspace;

            nfloat[] locations = { 0.0f, 1.0f };
            nfloat[] components = { 0.0f, 0.0f, 0.0f , 0.15f,  // Start color
                0.0f, 0.0f, 0.0f, 0.05f }; // End color

            myColorspace = CGColorSpace.CreateDeviceRGB (); // CGColorSpaceCreateDeviceRGB();
            myGradient = new CGGradient( myColorspace, components, locations);

            CGPoint startPoint = new CGPoint((float)rect.GetMidX(), (float)rect.GetMinY());
            CGPoint endPoint = new CGPoint((float)rect.GetMidX(), (float)rect.GetMaxY());

            ctx.SaveState ();
            ctx.AddPath( clipPath.CGPath);
            ctx.Clip ();
            ctx.DrawLinearGradient( (CGGradient)myGradient, (CGPoint)startPoint, (CGPoint)endPoint, (CGGradientDrawingOptions)0);

            myGradient.Dispose ();
            myColorspace.Dispose();
            ctx.RestoreState();

            // 4) highlight
            if (Highlighted)
            {
                // fill
                ctx.SetFillColor(UIColor.FromWhiteAlpha((nfloat)0.0f, (nfloat)0.1f).CGColor);
                ctx.AddPath( knobPath.CGPath);
                ctx.FillPath();
            }
        }

		public GradientTheme()
		{
			//BackgroundColor = UIColor.Clear;
			TextColor = UIColor.Black;
			TextShadowColor = UIColor.LightGray;
			TextShadowOffset = new SizeF(1, 0);
			
			gradient = new CGGradient(CGColorSpace.CreateDeviceRGB(), new float[] { 0.95f, 0.95f, 0.95f, 1, 0.85f, 0.85f, 0.85f, 1 }, new float[] { 0, 1 });
			
			DrawElementViewAction = (rect, context, cell) => { DrawElementView(rect, context, cell); };
		}

	public GradientDrawingView () : base ()
	{
		using (var rgb = CGColorSpace.CreateDeviceRGB ()) {
			nfloat[] colors = {
					204f / 255f, 224f / 255f, 244f / 255f, 10f,
					29f / 255f, 156f / 255f, 215f / 255f, 10f,
					0f / 255f,  50f / 255f, 126f / 255f, 10f,
				};
			gradient = new CGGradient (rgb, colors, null);
		}
	}

		public void DrawContentView(RectangleF rect, CGContext context, UITableViewElementCell cell)
		{
			context.SaveState();
			float r = 0;
			float g = 0;
			float b = 0;

			var gradient = new CGGradient(CGColorSpace.CreateDeviceRGB(), new float[] { r, g, b, 0.20f, r, g, b, 0.40f }, new float[] { 0, 1 });			
			context.DrawLinearGradient(gradient, new PointF(rect.Left, rect.Top), new PointF(rect.Left, rect.Bottom), CGGradientDrawingOptions.DrawsBeforeStartLocation);

			context.RestoreState();
		}

		public SampleOwnerDrawnElement (string text, DateTime sent, string from) : base(UITableViewCellStyle.Default, "sampleOwnerDrawnElement")
		{
			this.Subject = text;
			this.From = from;
			this.Sent = FormatDate(sent);
			CGColorSpace colorSpace = CGColorSpace.CreateDeviceRGB();
			gradient = new CGGradient(
			    colorSpace,
			    new float[] { 0.95f, 0.95f, 0.95f, 1, 
							  0.85f, 0.85f, 0.85f, 1},
				new float[] { 0, 1 } );
		}