color-interpolation.cs

using System;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Imaging;

class ColorInterpolationApplication {
	public static void Main() {
		Application.Run(new ColorInterpolation());
	}
}

class ColorInterpolation : Form {
	public ColorInterpolation() : base() {
		this.Paint += this.ColorInterpolation_Paint;
		this.SetStyle(ControlStyles.ResizeRedraw, true);
	}

	private static double Distance(int x, int y) {
		return Math.Sqrt(x * x + y * y);
	}

	private void ColorInterpolation_Paint(object sender, PaintEventArgs e) {
		int width = this.ClientSize.Width;
		int height = this.ClientSize.Height;

		using (var b = new Bitmap(width, height, PixelFormat.Format24bppRgb)) {
			var d = b.LockBits(this.ClientRectangle, ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);

			unsafe {
				byte* p = (byte*)d.Scan0;

				for (int y = 0; y < d.Height; y++) {
					for (int x = 0; x < d.Width; x++) {
						double rDist = Distance(x, y);
						double gDist = Distance(width - x, y);
						double bDist = Distance(x, height - y);

						byte r = (byte)(255 - Math.Min(255, rDist / width * 255));
						byte g = (byte)(255 - Math.Min(255, gDist / width * 255));
						byte bl = (byte)(255 - Math.Min(255, bDist / height * 255));

						*p++ = bl;
						*p++ = g;
						*p++ = r;
						*p++ = 255;
					}
				}
			}

			b.UnlockBits(d);

			e.Graphics.SetClip(this.ClientRectangle);
			e.Graphics.DrawImageUnscaled(b, 0, 0);
		}
	}
}