Task: Color wheel



C#: 

public MainWindow()
{
    InitializeComponent();
    RenderOptions.SetBitmapScalingMode(imgMain, BitmapScalingMode.HighQuality);
    imgMain.Source = new WriteableBitmap(480, 480, 96, 96, PixelFormats.Bgr32, null);
    
    DrawHue(100);
}

void DrawHue(int saturation)
{
    var bmp = (WriteableBitmap)imgMain.Source;

    int centerX = (int)bmp.Width / 2;
    int centerY = (int)bmp.Height / 2;
    int radius = Math.Min(centerX, centerY);
    int radius2 = radius - 40;

    bmp.Lock();
    unsafe{
        var buf = bmp.BackBuffer;
        IntPtr pixLineStart;
        for(int y=0; y < bmp.Height; y++){
            pixLineStart = buf + bmp.BackBufferStride * y;
            double dy = (y - centerY);
            for(int x=0; x < bmp.Width; x++){
                double dx = (x - centerX);
                double dist = Math.Sqrt(dx * dx + dy * dy);
                if (radius2 <= dist && dist <= radius) {
                    double theta = Math.Atan2(dy, dx);
                    double hue = (theta + Math.PI) / (2.0 * Math.PI);
                    *((int*)(pixLineStart + x * 4)) = HSB_to_RGB((int)(hue * 360), saturation, 100);
                }
            }
        }
    }
    bmp.AddDirtyRect(new Int32Rect(0, 0, 480, 480));
    bmp.Unlock();
}

static int HSB_to_RGB(int h, int s, int v)
{
    var rgb = new int[3];

    var baseColor = (h + 60) % 360 / 120;
    var shift = (h + 60) % 360 - (120 * baseColor + 60 );
    var secondaryColor = (baseColor + (shift >= 0 ? 1 : -1) + 3) % 3;

    
    rgb[baseColor] = 255;
    rgb[secondaryColor] = (int) ((Math.Abs(shift) / 60.0f) * 255.0f);

    
    for (var i = 0; i < 3; i++)
        rgb[i] += (int) ((255 - rgb[i]) * ((100 - s) / 100.0f));

    
    for (var i = 0; i < 3; i++)
        rgb[i] -= (int) (rgb[i] * (100-v) / 100.0f);

    return RGB2int(rgb[0], rgb[1], rgb[2]);
}

public static int RGB2int(int r, int g, int b) => r << 16 | g << 8 | b;



Java: import java.awt.*;
import javax.swing.*;

public class ColorWheel {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                ColorWheelFrame frame = new ColorWheelFrame();
                frame.setVisible(true);
            }
        });
    }

    private static class ColorWheelFrame extends JFrame {
        private ColorWheelFrame() {
            super("Color Wheel");
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            getContentPane().add(new ColorWheelPanel());
            pack();
        }
    }

    private static class ColorWheelPanel extends JComponent {
        private ColorWheelPanel() {
            setPreferredSize(new Dimension(400, 400));
        }
        public void paint(Graphics g) {
            Graphics2D g2 = (Graphics2D)g;
            int w = getWidth();
            int h = getHeight();
            int margin = 10;
            int radius = (Math.min(w, h) - 2 * margin)/2;
            int cx = w/2;
            int cy = h/2;
            float[] dist = {0.F, 1.0F};
            g2.setColor(Color.BLACK);
            g2.fillRect(0, 0, w, h);
            for (int angle = 0; angle < 360; ++angle) {
                Color color = hsvToRgb(angle, 1.0, 1.0);
                Color[] colors = {Color.WHITE, color};
                RadialGradientPaint paint = new RadialGradientPaint(cx, cy,
                        radius, dist, colors);
                g2.setPaint(paint);
                g2.fillArc(cx - radius, cy - radius, radius*2, radius*2,
                        angle, 1);
            }
        }
    }

    private static Color hsvToRgb(int h, double s, double v) {
        double hp = h/60.0;
        double c = s * v;
        double x = c * (1 - Math.abs(hp % 2.0 - 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;
        }
        r += m;
        g += m;
        b += m;
        return new Color((int)(r * 255), (int)(g * 255), (int)(b * 255));
    }
}