// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for details.

/* 
  THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF 
  ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO 
  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A 
  PARTICULAR PURPOSE. 
  
    This is sample code and is freely distributable. 
*/ 

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

namespace ImageManipulation
{
	/// <summary>
	/// Summary description for Class1.
	/// </summary>
	public unsafe abstract class Quantizer
	{
		/// <summary>
		/// Construct the quantizer
		/// </summary>
		/// <param name="singlePass">If true, the quantization only needs to loop through the source pixels once</param>
		/// <remarks>
		/// If you construct this class with a true value for singlePass, then the code will, when quantizing your image,
		/// only call the 'QuantizeImage' function. If two passes are required, the code will call 'InitialQuantizeImage'
		/// and then 'QuantizeImage'.
		/// </remarks>
		public Quantizer ( bool singlePass )
		{
			_singlePass = singlePass ;
		}

		/// <summary>
		/// Quantize an image and return the resulting output bitmap
		/// </summary>
		/// <param name="source">The image to quantize</param>
		/// <returns>A quantized version of the image</returns>
		public Bitmap Quantize ( Image source )
		{
			// Get the size of the source image
			int	height = source.Height ;
			int width = source.Width ;

			// And construct a rectangle from these dimensions
			Rectangle	bounds = new Rectangle ( 0 , 0 , width , height ) ;

			// First off take a 32bpp copy of the image
			Bitmap	copy = new Bitmap ( width , height , PixelFormat.Format32bppArgb ) ;

			// And construct an 8bpp version
			Bitmap	output = new Bitmap ( width , height , PixelFormat.Format8bppIndexed ) ;

			// Now lock the bitmap into memory
			using ( Graphics g = Graphics.FromImage ( copy ) )
			{
				g.PageUnit = GraphicsUnit.Pixel ;

				// Draw the source image onto the copy bitmap,
				// which will effect a widening as appropriate.
				g.DrawImageUnscaled  ( source , bounds ) ;
			}

			// Define a pointer to the bitmap data
			BitmapData	sourceData = null ;

			try
			{
				// Get the source image bits and lock into memory
				sourceData = copy.LockBits ( bounds , ImageLockMode.ReadOnly , PixelFormat.Format32bppArgb ) ;

				// Call the FirstPass function if not a single pass algorithm.
				// For something like an octree quantizer, this will run through
				// all image pixels, build a data structure, and create a palette.
				if ( !_singlePass )
					FirstPass ( sourceData , width , height ) ;

				// Then set the color palette on the output bitmap. I'm passing in the current palette 
				// as there's no way to construct a new, empty palette.
				output.Palette = this.GetPalette ( output.Palette ) ;

				// Then call the second pass which actually does the conversion
				SecondPass ( sourceData , output , width , height , bounds ) ;
			}
			finally
			{
				// Ensure that the bits are unlocked
				copy.UnlockBits ( sourceData ) ;
			}

			// Last but not least, return the output bitmap
			return output;
		}

		/// <summary>
		/// Execute the first pass through the pixels in the image
		/// </summary>
		/// <param name="sourceData">The source data</param>
		/// <param name="width">The width in pixels of the image</param>
		/// <param name="height">The height in pixels of the image</param>
		protected virtual void FirstPass ( BitmapData sourceData , int width , int height )
		{
			// Define the source data pointers. The source row is a byte to
			// keep addition of the stride value easier (as this is in bytes)
			byte*	pSourceRow = (byte*)sourceData.Scan0.ToPointer ( ) ;
			Int32*	pSourcePixel ;

			// Loop through each row
			for ( int row = 0 ; row < height ; row++ )
			{
				// Set the source pixel to the first pixel in this row
				pSourcePixel = (Int32*) pSourceRow ;

				// And loop through each column
				for ( int col = 0 ; col < width ; col++ , pSourcePixel++ )
					// Now I have the pixel, call the FirstPassQuantize function...
					InitialQuantizePixel ( (Color32*)pSourcePixel ) ;

				// Add the stride to the source row
				pSourceRow += sourceData.Stride ;
			}
		}

		/// <summary>
		/// Execute a second pass through the bitmap
		/// </summary>
		/// <param name="sourceData">The source bitmap, locked into memory</param>
		/// <param name="output">The output bitmap</param>
		/// <param name="width">The width in pixels of the image</param>
		/// <param name="height">The height in pixels of the image</param>
		/// <param name="bounds">The bounding rectangle</param>
		protected virtual void SecondPass ( BitmapData sourceData , Bitmap output , int width , int height , Rectangle bounds )
		{
			BitmapData	outputData = null ;

			try
			{
				// Lock the output bitmap into memory
				outputData = output.LockBits ( bounds , ImageLockMode.WriteOnly , PixelFormat.Format8bppIndexed ) ;

				// Define the source data pointers. The source row is a byte to
				// keep addition of the stride value easier (as this is in bytes)
				byte*	pSourceRow = (byte*)sourceData.Scan0.ToPointer ( ) ;
				Int32*	pSourcePixel = (Int32*)pSourceRow ;
				Int32*	pPreviousPixel = pSourcePixel ;

				// Now define the destination data pointers
				byte*	pDestinationRow = (byte*) outputData.Scan0.ToPointer();
				byte*	pDestinationPixel = pDestinationRow ;

				// And convert the first pixel, so that I have values going into the loop
				byte	pixelValue = QuantizePixel ( (Color32*)pSourcePixel ) ;

				// Assign the value of the first pixel
				*pDestinationPixel = pixelValue ;

				// Loop through each row
				for ( int row = 0 ; row < height ; row++ )
				{
					// Set the source pixel to the first pixel in this row
					pSourcePixel = (Int32*) pSourceRow ;

					// And set the destination pixel pointer to the first pixel in the row
					pDestinationPixel = pDestinationRow ;

					// Loop through each pixel on this scan line
					for ( int col = 0 ; col < width ; col++ , pSourcePixel++ , pDestinationPixel++ )
					{
						// Check if this is the same as the last pixel. If so use that value
						// rather than calculating it again. This is an inexpensive optimisation.
						if ( *pPreviousPixel != *pSourcePixel )
						{
							// Quantize the pixel
							pixelValue = QuantizePixel ( (Color32*)pSourcePixel ) ;

							// And setup the previous pointer
							pPreviousPixel = pSourcePixel ;
						}

						// And set the pixel in the output
						*pDestinationPixel = pixelValue ;
					}

					// Add the stride to the source row
					pSourceRow += sourceData.Stride ;

					// And to the destination row
					pDestinationRow += outputData.Stride ;
				}
			}
			finally
			{
				// Ensure that I unlock the output bits
				output.UnlockBits ( outputData ) ;
			}
		}

		/// <summary>
		/// Override this to process the pixel in the first pass of the algorithm
		/// </summary>
		/// <param name="pixel">The pixel to quantize</param>
		/// <remarks>
		/// This function need only be overridden if your quantize algorithm needs two passes,
		/// such as an Octree quantizer.
		/// </remarks>
		protected virtual void InitialQuantizePixel ( Color32* pixel )
		{
		}

		/// <summary>
		/// Override this to process the pixel in the second pass of the algorithm
		/// </summary>
		/// <param name="pixel">The pixel to quantize</param>
		/// <returns>The quantized value</returns>
		protected abstract byte QuantizePixel ( Color32* pixel ) ;

		/// <summary>
		/// Retrieve the palette for the quantized image
		/// </summary>
		/// <param name="original">Any old palette, this is overrwritten</param>
		/// <returns>The new color palette</returns>
		protected abstract ColorPalette GetPalette ( ColorPalette original ) ;

		/// <summary>
		/// Flag used to indicate whether a single pass or two passes are needed for quantization.
		/// </summary>
		private bool	_singlePass ;

		/// <summary>
		/// Struct that defines a 32 bpp colour
		/// </summary>
		/// <remarks>
		/// This struct is used to read data from a 32 bits per pixel image
		/// in memory, and is ordered in this manner as this is the way that
		/// the data is layed out in memory
		/// </remarks>
		[StructLayout(LayoutKind.Explicit)]
		public struct Color32
		{
			/// <summary>
			/// Holds the blue component of the colour
			/// </summary>
			[FieldOffset(0)]
			public byte Blue ;
			/// <summary>
			/// Holds the green component of the colour
			/// </summary>
			[FieldOffset(1)]
			public byte Green ;
			/// <summary>
			/// Holds the red component of the colour
			/// </summary>
			[FieldOffset(2)]
			public byte Red ;
			/// <summary>
			/// Holds the alpha component of the colour
			/// </summary>
			[FieldOffset(3)]
			public byte Alpha ;

			/// <summary>
			/// Permits the color32 to be treated as an int32
			/// </summary>
			[FieldOffset(0)]
			public int ARGB ;

			/// <summary>
			/// Return the color for this Color32 object
			/// </summary>
			public Color Color
			{
				get	{ return Color.FromArgb ( Alpha , Red , Green , Blue ) ; }
			}
		}
	}
}
