From 64bc85565239e9e810c7bdc67375a20fb0254b69 Mon Sep 17 00:00:00 2001
From: RKrom <robin@getgreenshot.org>
Date: Wed, 21 Mar 2012 13:12:19 +0000
Subject: [PATCH] Fixed missing alpha blending and optimized performance.

git-svn-id: http://svn.code.sf.net/p/greenshot/code/trunk@1718 7dccd23d-a4a3-4e1f-8c07-b4c1b4018ab4
---
 GreenshotPlugin/Core/BitmapBuffer.cs    | 36 ++++++++++++++++++++---
 GreenshotPlugin/Core/QuantizerHelper.cs | 38 ++-----------------------
 2 files changed, 34 insertions(+), 40 deletions(-)

diff --git a/GreenshotPlugin/Core/BitmapBuffer.cs b/GreenshotPlugin/Core/BitmapBuffer.cs
index e12600cd2..075931156 100644
--- a/GreenshotPlugin/Core/BitmapBuffer.cs
+++ b/GreenshotPlugin/Core/BitmapBuffer.cs
@@ -33,6 +33,22 @@ namespace GreenshotPlugin.Core {
 		private static log4net.ILog LOG = log4net.LogManager.GetLogger(typeof(BitmapBuffer));
 		private bool clone;
 		private Bitmap bitmap;
+		private static int[] factors = new int[256];
+		private static int[] remainings = new int[256];
+
+		static BitmapBuffer() {
+			// Pre calculate for alpha blending
+			for (int i = 0; i < 256; i++) {
+				int factor = 0x10000 * i / 255;
+				factors[i] = factor;
+				remainings[i] = (0x10000 * 255) - factor;
+			}
+		}
+
+		public static Color BackgroundBlendColor {
+			get;
+			set;
+		}
 
 		/// <summary>
 		/// Get the bitmap, you will always need to dispose the returned bitmap!!
@@ -309,16 +325,28 @@ namespace GreenshotPlugin.Core {
 		}
 
 		/// <summary>
-		/// Retrieve the color, without alpha, at location x,y
+		/// Retrieve the color, without alpha (is blended), at location x,y
 		/// Before the first time this is called the Lock() should be called once!
 		/// </summary>
 		/// <param name="x">X coordinate</param>
 		/// <param name="y">Y Coordinate</param>
 		/// <returns>Color</returns>
 		public Color GetColorAtWithoutAlpha(int x, int y) {
-			if(x>=0 && y>=0 && x<rect.Width && y<rect.Height) {
-				int offset = x*bytesPerPixel+y*stride;
-				return Color.FromArgb(255, pointer[rIndex+offset], pointer[gIndex+offset], pointer[bIndex+offset]);
+			if (x >= 0 && y >= 0 && x < rect.Width && y < rect.Height) {
+				int offset = x * bytesPerPixel + y * stride;
+				int a = (aIndex == -1) ? (byte)255 : pointer[aIndex + offset];
+				int red = pointer[rIndex + offset];
+				int green = pointer[gIndex + offset];
+				int blue = pointer[bIndex + offset];
+
+				if (a < 255) {
+					int aMult = factors[a];
+					int rem = remainings[a];
+					red = (red * rem + BackgroundBlendColor.R * aMult) >> 16;
+					green = (green * rem + BackgroundBlendColor.G * aMult) >> 16;
+					blue = (blue * rem + BackgroundBlendColor.B * aMult) >> 16;
+				}
+				return Color.FromArgb(255, red, green, blue);
 			} else {
 				return Color.Empty;
 			}
diff --git a/GreenshotPlugin/Core/QuantizerHelper.cs b/GreenshotPlugin/Core/QuantizerHelper.cs
index 37490d4c6..92f6fc8a6 100644
--- a/GreenshotPlugin/Core/QuantizerHelper.cs
+++ b/GreenshotPlugin/Core/QuantizerHelper.cs
@@ -71,8 +71,6 @@ namespace GreenshotPlugin.Core {
 
 	public class WuQuantizer {
 		private static log4net.ILog LOG = log4net.LogManager.GetLogger(typeof(WuQuantizer));
-		private static readonly Color BackgroundColor;
-		private static readonly Double[] Factors;
 
 		private const Int32 MAXCOLOR = 512;
 		private const Int32 RED = 2;
@@ -102,14 +100,6 @@ namespace GreenshotPlugin.Core {
 		private Bitmap sourceBitmap;
 		private Bitmap resultBitmap;
 
-		static WuQuantizer() {
-			BackgroundColor = Color.White;
-			Factors = new Double[256];
-			for (Int32 value = 0; value < 256; value++) {
-				Factors[value] = value / 255.0;
-			}
-		}
-
 		/// <summary>
 		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
 		/// </summary>
@@ -157,8 +147,7 @@ namespace GreenshotPlugin.Core {
 					bbbDest.Lock();
 					for (int y = 0; y < bbbSrc.Height; y++) {
 						for (int x = 0; x < bbbSrc.Width; x++) {
-							Color color = bbbSrc.GetColorAt(x, y);
-							color = ConvertAlpha(color);
+							Color color = bbbSrc.GetColorAtWithoutAlpha(x, y);
 							// To count the colors
 							int index = color.ToArgb() & 0x00ffffff;
 							// Check if we already have this color
@@ -270,8 +259,7 @@ namespace GreenshotPlugin.Core {
 					byte bestMatch;
 					for (int y = 0; y < bbbSrc.Height; y++) {
 						for (int x = 0; x < bbbSrc.Width; x++) {
-							Color color = bbbSrc.GetColorAt(x, y);
-
+							Color color = bbbSrc.GetColorAtWithoutAlpha(x, y);
 							// Check if we already matched the color
 							if (!lookup.ContainsKey(color)) {
 								// If not we need to find the best match
@@ -329,28 +317,6 @@ namespace GreenshotPlugin.Core {
 			return resultBitmap;
 		}
 
-		/// <summary>
-		/// Converts the alpha blended color to a non-alpha blended color.
-		/// </summary>
-		/// <param name="color">The alpha blended color (ARGB).</param>
-		/// <returns>The non-alpha blended color (RGB).</returns>
-		private static Color ConvertAlpha(Color color) {
-			Color result = color;
-
-			if (color.A < 255) {
-				// performs a alpha blending (second color is BackgroundColor, by default a Control color)
-				Double colorFactor = Factors[color.A];
-				Double backgroundFactor = Factors[255 - color.A];
-				Int32 red = (Int32)(color.R * colorFactor + BackgroundColor.R * backgroundFactor);
-				Int32 green = (Int32)(color.G * colorFactor + BackgroundColor.G * backgroundFactor);
-				Int32 blue = (Int32)(color.B * colorFactor + BackgroundColor.B * backgroundFactor);
-				Int32 argb = 255 << 24 | red << 16 | green << 8 | blue;
-				result = Color.FromArgb(argb);
-			}
-
-			return result;
-		}
-
 		/// <summary>
 		/// Converts the histogram to a series of moments.
 		/// </summary>