ColorWheel.cs

This code demonstrates how to draw a color wheel into a RGBA ImageView. The part outside the wheel is transparent, using alpha channel.

using IOLink;
using System;
using System.Numerics;
using System.Runtime.Intrinsics;
 
namespace Examples
{
    public class ColorWheel
    {
        private static Vector3u8 HsvToRgb(double h, double s, double v)
        {
            double hp = h / 60.0;
            double c = s * v;
            double x = c * (1 - Math.Abs((hp % 2) - 1));
            double m = v - c;
            double r = 0, g = 0, b = 0;
            if (hp <= 1)
            {
                r = c;
                g = x;
            }
            else if (hp <= 2)
            {
                r = x;
                g = c;
            }
            else if (hp <= 3)
            {
                g = c;
                b = x;
            }
            else if (hp <= 4)
            {
                g = x;
                b = c;
            }
            else if (hp <= 5)
            {
                r = x;
                b = c;
            }
            else
            {
                r = c;
                b = x;
            }
            Vector3d rgb_double = new Vector3d( r, g, b);
            rgb_double += Vector3d.CreateUniform(m);
            rgb_double *= 255.0;
            return new Vector3u8((byte)rgb_double[0], (byte)rgb_double[1], (byte)rgb_double[2]);
        }
 
        private static ImageView Generate(VectorXu64 shape)
        {
            // first we can check if given shape has exactly 2
            // dimensions
            if (shape.Size() != 2)
            {
                throw new ApplicationException("Shape must have 2 dimensions");
            }
 
            // To create a RGBA ImageView, the datatype of the
            // image must have 4 components, and so should be be
            // VEC4_XXX (with XXX: INT8, INT16, INT32, INT64,
            // UINT8, ...) We choose VEC4_UINT8 as the datatype
            // for this example.
            DataType dt = DataTypeId.VEC4_UINT8;
 
            // create an image view in CPU memory
            ImageView image = ImageViewFactory.Allocate(shape, dt);
 
            // indicate the created image is a 2D IMAGE with RGB
            // color interpretation and alpha channel
            image.AxesInterpretation = ImageTypeId.IMAGE;
            image.ImageInterpretation = ImageInterpretation.RGB;
            image.HasAlpha = true;
 
            // draw the color wheel
            // all pixels outside the wheel are transparent
            // (alpha=0)
            Vector2d center = new Vector2d(shape[0] / 2.0, shape[1] / 2.0);
 
            for (ulong y = 0; y < shape[1]; ++y)
            {
                for (ulong x = 0; x < shape[0]; ++x)
                {
                    Vector2d position = new Vector2d((double)x, (double)y);
                    Vector2d delta = position - center;
                    VectorXu64 positionPixel = new VectorXu64(x, y);
                    double r = delta.Length();
                    if (r > center[0])
                    {
                        // write transparent pixel
                        // use a byte array with 4 elements
                        // (RGBA)
                        byte[] pixVal = { 0, 0, 0, 0 };
                        image.Write(positionPixel, pixVal);
                    }
                    else
                    {
                        // determine HSV value for current pixel
                        // position
                        double h = Math.Atan2(delta[1], delta[0]) * 180 / Math.PI + 180;
                        double s = r / center[0];
                        double v = 1;
                        // convert HSV to RGB
                        var rgb = ColorWheel.HsvToRgb(h, s, v);
                        // write RGBA pixel (with alpha = 255)
                        // use a byte array with 4 elements
                        // (RGBA)
                        byte[] pixVal = { rgb[0], rgb[1], rgb[2], 255 };
                        image.Write(positionPixel, pixVal);
                    }
                }
            }
            return image;
        }
 
        public static void Main(string[] args)
        {
            ImageView image = Generate(new VectorXu64(512, 512));
 
            Console.WriteLine("Generated image: " + image.ToString());
 
            Console.WriteLine("SUCCESS");
        }
    }
}