#674 – Mapping Mouse Position to Color, part II

In the previous post, we used the mouse position to map to the Hue and Saturation portions of an HSV color value and then set the background color of a window based on the mouse position.

This post adds to the example, by using the mouse wheel to control the Value portion of the color (which ranges from 0.0 to 1.0).

Here’s the updated XAML:

<Window Name="win1" x:Class="WpfApplication1.MainWindow"
        Title="Color from Mouse Position"
        MouseMove="win1_MouseMove_1" MouseWheel="win1_MouseWheel_1">

    <Canvas x:Name="canv1" Width="400" Height="400">
        <Label x:Name="lblInfo" Content="{Binding RGBInfo}" HorizontalAlignment="Center" />
        <Ellipse x:Name="ellipseCenter" Stroke="Black" Width="2" Height="2" Fill="Black" Canvas.Left="199" Canvas.Top="199"/>

And the updated code-behind:

    public partial class MainWindow : Window, INotifyPropertyChanged
        SolidColorBrush backBrush = new SolidColorBrush();
        double value = 1.0;

        public MainWindow()

            this.DataContext = this;
            win1.Background = backBrush;

        private string rgbInfo;
        public string RGBInfo
            get { return rgbInfo; }
                if (value != rgbInfo)
                    rgbInfo = value;

        private void win1_MouseMove_1(object sender, MouseEventArgs e)

        private void win1_MouseWheel_1(object sender, MouseWheelEventArgs e)
            if ((e.Delta > 0) && (value < 1.0))
                value += 0.1;
            else if ((e.Delta < 0) && (value > 0.0))
                value -= 0.1;


        private void RecalcColor(Point mousePos)
            double radius = (canv1.ActualWidth / 2);

            double hue;
            double saturation;
            Color c = ColorFromMousePosition(mousePos, radius, out hue, out saturation);
            backBrush.Color = c;
            RGBInfo = string.Format("R={0}, G={1}, B={2}.  H={3:F1}, S={4:F1}, V={5:F1}",
                c.R, c.G, c.B,
                hue, saturation, value);

            if (value < 0.5)
                lblInfo.Foreground = Brushes.White;
                ellipseCenter.Stroke = Brushes.White;
                lblInfo.Foreground = Brushes.Black;
                ellipseCenter.Stroke = Brushes.Black;

        private Color ColorFromMousePosition(Point mousePos, double radius, out double hue, out double saturation)
            // Position relative to center of canvas
            double xRel = mousePos.X - radius;
            double yRel = mousePos.Y - radius;

            // Hue is angle in deg, 0-360
            double angleRadians = Math.Atan2(yRel, xRel);
            hue = angleRadians * (180 / Math.PI);
            if (hue < 0)
                hue = 360 + hue;

            // Saturation is distance from center
            saturation = Math.Min(Math.Sqrt(xRel * xRel + yRel * yRel) / radius, 1.0);

            byte r, g, b;
            ColorUtil.HsvToRgb(hue, saturation, value, out r, out g, out b);
            return Color.FromRgb(r, g, b);

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged(string prop)
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));

(See the earlier post for the ColorUtil code).
We can now roll the mouse wheel down to reduce the value, making the colors darker.


About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

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