Gradients made easy

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

public class ColorWheel:IDisposable 
{

	// These resources should be disposed
	// of when you're done with them.
	private Graphics g;
	private Region colorRegion;
	private Region brightnessRegion;
	private Bitmap colorImage;

	public delegate void ColorChangedEventHandler( object sender, ColorChangedEventArgs e);
	public ColorChangedEventHandler ColorChanged;

	// Keep track of the current mouse state. 
	public enum MouseState
	{
		MouseUp,
		ClickOnColor,
		DragInColor,
		ClickOnBrightness,
		DragInBrightness,
		ClickOutsideRegion,
		DragOutsideRegion,
	}
	private MouseState currentState = MouseState.MouseUp;

	// The code needs to convert back and forth between 
	// degrees and radians. There are 2*PI radians in a 
	// full circle, and 360 degrees. This constant allows
	// you to convert back and forth.
	private const double DEGREES_PER_RADIAN = 180.0 / Math.PI;

	// COLOR_COUNT represents the number of distinct colors
	// used to create the circular gradient. Its value 
	// is somewhat arbitrary -- change this to 6, for 
	// example, to see what happens. 1536 (6 * 256) seems 
	// a good compromise -- it's enough to get a full 
	// range of colors, but it doesn't overwhelm the processor
	// attempting to generate the image. The color wheel
	// contains 6 sections, and each section displays 
	// 256 colors. Seems like a reasonable compromise.
	private const int COLOR_COUNT = 6 * 256;

	private Point centerPoint;
	private int radius;

	private Rectangle colorRectangle;
	private Rectangle brightnessRectangle;
	private Rectangle selectedColorRectangle;
	private int brightnessX;
	private double brightnessScaling;

	// selectedColor is the actual value selected
	// by the user. fullColor is the same color, 
	// with its brightness set to 255.
	private Color selectedColor = Color.White;
	private Color fullColor;

	private ColorHandler.RGB RGB;
	private ColorHandler.HSV HSV;

	// Locations for the two "pointers" on the form.
	private Point colorPoint;
	private Point brightnessPoint;

	private int brightness;
	private int brightnessMin;
	private int brightnessMax;

	public ColorWheel(  Rectangle colorRectangle,  Rectangle brightnessRectangle,  Rectangle selectedColorRectangle) 
	{

		// Caller must provide locations for color wheel
		// (colorRectangle), brightness "strip" (brightnessRectangle)
		// and location to display selected color (selectedColorRectangle).

		using (GraphicsPath path = new GraphicsPath())
		{
			// Store away locations for later use. 
			this.colorRectangle = colorRectangle;
			this.brightnessRectangle = brightnessRectangle;
			this.selectedColorRectangle = selectedColorRectangle;

			// Calculate the center of the circle.
			// Start with the location, then offset
			// the point by the radius.
			// Use the smaller of the width and height of
			// the colorRectangle value.
			this.radius = (int) Math.Min(colorRectangle.Width, colorRectangle.Height) / 2;
			this.centerPoint = colorRectangle.Location;
			this.centerPoint.Offset(radius, radius);

			// Start the pointer in the center.
			this.colorPoint = this.centerPoint;

			// Create a region corresponding to the color circle.
			// Code uses this later to determine if a specified
			// point is within the region, using the IsVisible 
			// method.
			path.AddEllipse(colorRectangle);
			colorRegion = new Region(path);

			// set { the range for the brightness selector.
			this.brightnessMin = this.brightnessRectangle.Top;
			this.brightnessMax = this.brightnessRectangle.Bottom;

			// Create a region corresponding to the
			// brightness rectangle, with a little extra 
			// "breathing room". 
      
			path.AddRectangle(new Rectangle(brightnessRectangle.Left, brightnessRectangle.Top - 10, brightnessRectangle.Width + 10, brightnessRectangle.Height + 20));
			// Create region corresponding to brightness
			// rectangle. Later code uses this to 
			// determine if a specified point is within
			// the region, using the IsVisible method.
			brightnessRegion = new Region(path);

			// Set the location for the brightness indicator "marker".
			// Also calculate the scaling factor, scaling the height
			// to be between 0 and 255. 
			brightnessX = brightnessRectangle.Left + brightnessRectangle.Width;
			brightnessScaling = (double) 255 / (brightnessMax - brightnessMin);

			// Calculate the location of the brightness
			// pointer. Assume it's at the highest position.
			brightnessPoint =  new Point(brightnessX, brightnessMax);

			// Create the bitmap that contains the circular gradient.
			CreateGradient();
		} 
	}
	
	protected void OnColorChanged(ColorHandler.RGB RGB,  ColorHandler.HSV HSV) 
	{
		ColorChangedEventArgs  e = new ColorChangedEventArgs(RGB, HSV);
		ColorChanged(this, e);
	}

	public Color Color  
	{
		get 
		{
			return selectedColor;
		}
	}

	void IDisposable.Dispose()
	{
    // Dispose of graphic resources
    if (colorImage != null)
      colorImage.Dispose();
    if (colorRegion != null)
      colorRegion.Dispose();
    if (brightnessRegion != null)
      brightnessRegion.Dispose();
    if (g != null)
      g.Dispose();
	}

	public void SetMouseUp() 
	{
		// Indicate that the user has
		// released the mouse.
		currentState = MouseState.MouseUp;
	}

	public void Draw( Graphics g, ColorHandler.HSV HSV ) 
	{
		// Given HSV values, update the screen.
		this.g = g;
		this.HSV = HSV;
		CalcCoordsAndUpdate(this.HSV);
		UpdateDisplay();
	}

	public void Draw( Graphics g, ColorHandler.RGB RGB) 
	{
		// Given RGB values, calculate HSV and then update the screen.
		this.g = g;
		this.HSV = ColorHandler.RGBtoHSV(RGB);
		CalcCoordsAndUpdate(this.HSV);
		UpdateDisplay();
	}

	public void Draw(Graphics g, Point mousePoint) 
	{
		// You've moved the mouse. 
		// Now update the screen to match.

		double distance;
		int degrees;
		Point delta;
		Point newColorPoint;
		Point newBrightnessPoint;
		Point newPoint;

		// Keep track of the previous color pointer point, 
		// so you can put the mouse there in case the 
		// user has clicked outside the circle.
		newColorPoint = colorPoint;
		newBrightnessPoint = brightnessPoint;

		// Store this away for later use.
		this.g = g;

		if ( currentState == MouseState.MouseUp ) 
		{
			if (! mousePoint.IsEmpty ) 
			{
				if ( colorRegion.IsVisible(mousePoint) ) 
				{
					// Is the mouse point within the color circle?
					// If so, you just clicked on the color wheel.
					currentState = MouseState.ClickOnColor;
				} 
				else if ( brightnessRegion.IsVisible(mousePoint) ) 
				{
					// Is the mouse point within the brightness area?
					// You clicked on the brightness area.
					currentState = MouseState.ClickOnBrightness;
				} 
				else 
				{
					// Clicked outside the color and the brightness
					// regions. In that case, just put the 
					// pointers back where they were.
					currentState = MouseState.ClickOutsideRegion;
				}
			}
		}

		switch (currentState)
		{
			case MouseState.ClickOnBrightness:
			case MouseState.DragInBrightness:
				// Calculate new color information
				// based on the brightness, which may have changed.
				newPoint = mousePoint;
				if ( newPoint.Y < brightnessMin ) 
				{
					newPoint.Y = brightnessMin;
				} 
				else if ( newPoint.Y > brightnessMax ) 
				{
					newPoint.Y = brightnessMax;
				}
				newBrightnessPoint = new Point(brightnessX, newPoint.Y);
				brightness = (int)((brightnessMax - newPoint.Y) * brightnessScaling);
				HSV.value = brightness;
				RGB = ColorHandler.HSVtoRGB(HSV);
				break;

			case MouseState.ClickOnColor:
			case MouseState.DragInColor:
				// Calculate new color information
				// based on selected color, which may have changed.
				newColorPoint = mousePoint;

				// Calculate x and y distance from the center,
				// and then calculate the angle corresponding to the
				// new location.
				delta = new Point(
					mousePoint.X - centerPoint.X, mousePoint.Y - centerPoint.Y);
				degrees = CalcDegrees(delta);

				// Calculate distance from the center to the new point 
				// as a fraction of the radius. Use your old friend, 
				// the Pythagorean theorem, to calculate this value.
				distance = Math.Sqrt(delta.X * delta.X + delta.Y * delta.Y) / radius;

				if ( currentState == MouseState.DragInColor ) 
				{
					if ( distance > 1 ) 
					{
						// Mouse is down, and outside the circle, but you 
						// were previously dragging in the color circle. 
						// What to do?
						// In that case, move the point to the edge of the 
						// circle at the correct angle.
						distance = 1;
						newColorPoint = GetPoint(degrees, radius, centerPoint);
					}
				}

				// Calculate the new HSV and RGB values.
				HSV.Hue = (int)(degrees * 255 / 360);
				HSV.Saturation = (int)(distance * 255);
				HSV.value = brightness;
				RGB = ColorHandler.HSVtoRGB(HSV);
				fullColor = ColorHandler.HSVtoColor(HSV.Alpha, HSV.Hue, HSV.Saturation, 255);
				break;
		}
		selectedColor = ColorHandler.HSVtoColor(HSV);

		// Raise an event back to the parent form,
		// so the form can update any UI it's using 
		// to display selected color values.
		OnColorChanged(RGB, HSV);

		// On the way out, set the new state.
		switch (currentState)
		{
			case MouseState.ClickOnBrightness:
				currentState = MouseState.DragInBrightness;
				break;
			case MouseState.ClickOnColor:
				currentState = MouseState.DragInColor;
				break;
			case MouseState.ClickOutsideRegion:
				currentState = MouseState.DragOutsideRegion;
				break;
		}

		// Store away the current points for next time.
		colorPoint = newColorPoint;
		brightnessPoint = newBrightnessPoint;

		// Draw the gradients and points. 
		UpdateDisplay();
	}

	private Point CalcBrightnessPoint(int brightness) 
	{
		// Take the value for brightness (0 to 255), scale to the 
		// scaling used in the brightness bar, then add the value 
		// to the bottom of the bar. return the correct point at which 
		// to display the brightness pointer.
		return new Point(brightnessX,     
			(int)(brightnessMax - brightness / brightnessScaling));
	}

	private void UpdateDisplay() 
	{
		// Update the gradients, and place the 
		// pointers correctly based on colors and 
		// brightness.

		using (Brush selectedBrush = new SolidBrush(selectedColor))
		{
			// Draw the saved color wheel image.
			g.DrawImage(colorImage, colorRectangle);

			// Draw the "selected color" rectangle.
			g.FillRectangle(selectedBrush, selectedColorRectangle);

			// Draw the "brightness" rectangle.
			DrawLinearGradient(fullColor);
			// Draw the two pointers.
			DrawColorPointer(colorPoint);
			DrawBrightnessPointer(brightnessPoint);
		} 
	}

	private void CalcCoordsAndUpdate( ColorHandler.HSV HSV) 
	{
		// Convert color to real-world coordinates and then calculate
		// the various points. HSV.Hue represents the degrees (0 to 360), 
		// HSV.Saturation represents the radius. 
		// This procedure doesn't draw anything--it simply 
		// updates class-level variables. The UpdateDisplay
		// procedure uses these values to update the screen.

		// Given the angle (HSV.Hue), and distance from 
		// the center (HSV.Saturation), and the center, 
		// calculate the point corresponding to 
		// the selected color, on the color wheel.
		colorPoint = GetPoint((double)HSV.Hue / 255 * 360, 
			(double)HSV.Saturation / 255 * radius, 
			centerPoint);

		// Given the brightness (HSV.value), calculate the 
		// point corresponding to the brightness indicator.
		brightnessPoint = CalcBrightnessPoint(HSV.value);

		// Store information about the selected color.
		brightness = HSV.value;
		selectedColor = ColorHandler.HSVtoColor(HSV);
		RGB = ColorHandler.HSVtoRGB(HSV);

		// The full color is the same as HSV, except that the 
		// brightness is set to full (255). This is the top-most
		// color in the brightness gradient.
		fullColor = ColorHandler.HSVtoColor(HSV.Alpha, HSV.Hue, HSV.Saturation, 255);
	}

	private void DrawLinearGradient( Color TopColor) 
	{
		// Given the top color, draw a linear gradient
		// ranging from black to the top color. Use the 
		// brightness rectangle as the area to fill.
		using (LinearGradientBrush lgb = 
						 new LinearGradientBrush(brightnessRectangle, TopColor, 
						 Color.Black, LinearGradientMode.Vertical))
		{
			g.FillRectangle(lgb, brightnessRectangle);
		} 
	}

	private int CalcDegrees(Point pt) 
	{
		int degrees;

		if ( pt.X == 0 ) 
		{
			// The point is on the y-axis. Determine whether 
			// it's above or below the x-axis, and return the 
			// corresponding angle. Note that the orientation of the
			// y-coordinate is backwards. That is, A positive Y value 
			// indicates a point BELOW the x-axis.
			if ( pt.Y > 0 ) 
			{
				degrees = 270;
			} 
			else 
			{
				degrees = 90;
			}
		} 
		else 
		{
			// This value needs to be multiplied
			// by -1 because the y-coordinate
			// is opposite from the normal direction here.
			// That is, a y-coordinate that's "higher" on 
			// the form has a lower y-value, in this coordinate
			// system. So everything's off by a factor of -1 when
			// performing the ratio calculations.
			degrees = (int)(-Math.Atan((double)pt.Y / pt.X) * DEGREES_PER_RADIAN);

			// If the x-coordinate of the selected point
			// is to the left of the center of the circle, you 
			// need to add 180 degrees to the angle. ArcTan only
			// gives you a value on the right-hand side of the circle.
			if ( pt.X < 0 ) 
			{
				degrees += 180;
			}

			// Ensure that the return value is 
			// between 0 and 360.
			degrees = (degrees + 360) % 360;
		}
		return degrees;
	}

	private void CreateGradient() 
	{
		// Create a new PathGradientBrush, supplying
		// an array of points created by calling
		// the GetPoints method.
		using (PathGradientBrush pgb = 
			new PathGradientBrush(GetPoints(radius, new Point(radius, radius))))
		{
			// Set the various properties. Note the SurroundColors
			// property, which contains an array of points, 
			// in a one-to-one relationship with the points
			// that created the gradient.
			pgb.CenterColor = Color.White;
			pgb.CenterPoint = new PointF(radius, radius);
			pgb.SurroundColors = GetColors();

			// Create a new bitmap containing
			// the color wheel gradient, so the 
			// code only needs to do all this 
			// work once. Later code uses the bitmap
			// rather than recreating the gradient.
			colorImage = new Bitmap(
				colorRectangle.Width, colorRectangle.Height, 
				PixelFormat.Format32bppArgb);
	
			using (Graphics newGraphics = 
							 Graphics.FromImage(colorImage))
			{
				newGraphics.FillEllipse(pgb, 0, 0, 
					colorRectangle.Width, colorRectangle.Height);
			}
		} 
	}

	private Color[] GetColors() 
	{
		// Create an array of COLOR_COUNT
		// colors, looping through all the 
		// hues between 0 and 255, broken
		// into COLOR_COUNT intervals. HSV is
		// particularly well-suited for this, 
		// because the only value that changes
		// as you create colors is the Hue.
		Color[] Colors = new Color[COLOR_COUNT];

		for ( int i = 0 ; i <= COLOR_COUNT - 1; i++)
			Colors[i] = ColorHandler.HSVtoColor(255, (int)((double)(i * 255) / COLOR_COUNT), 255, 255);
		return Colors;
	}

	private Point[] GetPoints(double radius,  Point centerPoint) 
	{
		// Generate the array of points that describe
		// the locations of the COLOR_COUNT colors to be 
		// displayed on the color wheel.
		Point[] Points = new Point[COLOR_COUNT];

		for ( int i = 0 ; i <= COLOR_COUNT - 1; i++ )
			Points[i] = GetPoint((double)(i * 360) / COLOR_COUNT, radius, centerPoint);
		return Points;
	}

	private Point GetPoint(double degrees, double radius, Point centerPoint) 
	{
		// Given the center of a circle and its radius, along
		// with the angle corresponding to the point, find the coordinates. 
		// In other words, conver  t from polar to rectangular coordinates.
		double radians = degrees / DEGREES_PER_RADIAN;

		return new Point((int)(centerPoint.X + Math.Floor(radius * Math.Cos(radians))), 
			(int)(centerPoint.Y - Math.Floor(radius * Math.Sin(radians))));
	}

	private void DrawColorPointer( Point pt) 
	{
		// Given a point, draw the color selector. 
		// The constant SIZE represents half
		// the width -- the square will be twice
		// this value in width and height.
		const int SIZE = 5;
		g.DrawEllipse(Pens.Black, 
			pt.X - SIZE, pt.Y - SIZE, SIZE * 2, SIZE * 2);
        g.FillEllipse(Brushes.Black,
        pt.X - 3, pt.Y - 3, 6, 6);
    }

	private void DrawBrightnessPointer( Point pt) 
	{
		// Draw a triangle for the 
		// brightness indicator that "points"
		// at the provided point.
		const int HEIGHT = 10;
		const int WIDTH = 7;

		Point[] Points = new Point[3];
		Points[0] = pt;
		Points[1] = new Point(pt.X + WIDTH, pt.Y + HEIGHT / 2);
		Points[2] = new Point(pt.X + WIDTH, pt.Y - HEIGHT / 2);
		g.DrawPolygon(new Pen(Color.Black), Points);
	}
}