Creating Bitmap Regions for Forms and Buttons

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace BitmapRegionTest
{
	/// <summary>
	/// Summary description for BitmapRegion.
	/// </summary>
	public class BitmapRegion
	{
		public BitmapRegion()
		{}

		/// <summary>
		/// Create and apply the region on the supplied control
		/// </summary>
		/// <param name="control">The Control object to apply the region to</param>
		/// <param name="bitmap">The Bitmap object to create the region from</param>
		public static void CreateControlRegion(Control control, Bitmap bitmap)
		{
			// Return if control and bitmap are null
			if(control == null || bitmap == null)
				return;
			
			// Set our control's size to be the same as the bitmap
			control.Width = bitmap.Width;
			control.Height = bitmap.Height;

			// Check if we are dealing with Form here
			if(control is System.Windows.Forms.Form)
			{
				// Cast to a Form object
				Form form = (Form)control;

				// Set our form's size to be a little larger that the bitmap just 
				// in case the form's border style is not set to none in the first place
				form.Width += 15;
				form.Height += 35;

				// No border
				form.FormBorderStyle = FormBorderStyle.None;

				// Set bitmap as the background image
				form.BackgroundImage = bitmap;

				// Calculate the graphics path based on the bitmap supplied
				GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);

				// Apply new region
				form.Region = new Region(graphicsPath);
			}

			// Check if we are dealing with Button here
			else if(control is System.Windows.Forms.Button)
			{
				// Cast to a button object
				Button button = (Button)control;

				// Do not show button text
				button.Text = "";
				
				// Change cursor to hand when over button
				button.Cursor = Cursors.Hand;

				// Set background image of button
				button.BackgroundImage = bitmap;
				
				// Calculate the graphics path based on the bitmap supplied
				GraphicsPath graphicsPath = CalculateControlGraphicsPath(bitmap);

				// Apply new region
				button.Region = new Region(graphicsPath);
			}
		}

		/// <summary>
		/// Calculate the graphics path that representing the figure in the bitmap 
		/// excluding the transparent color which is the top left pixel.
		/// </summary>
		/// <param name="bitmap">The Bitmap object to calculate our graphics path from</param>
		/// <returns>Calculated graphics path</returns>
		private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)
		{
			// Create GraphicsPath for our bitmap calculation
			GraphicsPath graphicsPath = new GraphicsPath();

			// Use the top left pixel as our transparent color
			Color colorTransparent = bitmap.GetPixel(0, 0);

			// This is to store the column value where an opaque pixel is first found.
			// This value will determine where we start scanning for trailing opaque pixels.
			int colOpaquePixel = 0;

			// Go through all rows (Y axis)
			for(int row = 0; row < bitmap.Height; row ++)
			{
				// Reset value
				colOpaquePixel = 0;

				// Go through all columns (X axis)
				for(int col = 0; col < bitmap.Width; col ++)
				{
					// If this is an opaque pixel, mark it and search for anymore trailing behind
					if(bitmap.GetPixel(col, row) != colorTransparent)
					{
						// Opaque pixel found, mark current position
						colOpaquePixel = col;

						// Create another variable to set the current pixel position
						int colNext = col;

						// Starting from current found opaque pixel, search for anymore opaque pixels 
						// trailing behind, until a transparent pixel is found or minimum width is reached
						for(colNext = colOpaquePixel; colNext < bitmap.Width; colNext ++)
							if(bitmap.GetPixel(colNext, row) == colorTransparent)
								break;

						// Form a rectangle for line of opaque pixels found and add it to our graphics path
						graphicsPath.AddRectangle(new Rectangle(colOpaquePixel, row, colNext - colOpaquePixel, 1));

						// No need to scan the line of opaque pixels just found
						col = colNext;
					}
				}
			}

			// Return calculated graphics path
			return graphicsPath;
		}
	}
}