From cf82096887d8fc5ed9a1efd85d8ca1522857f5ff Mon Sep 17 00:00:00 2001
From: Alexey 'Cluster' Avdyukhin <clusterrr@clusterrr.com>
Date: Thu, 27 Oct 2022 20:46:03 +0400
Subject: Minor optimization.

---
 NesTiler/ColorExtensions.cs |  5 +++--
 NesTiler/FastBitmap.cs      | 31 ++++++++++++++++++-------------
 2 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/NesTiler/ColorExtensions.cs b/NesTiler/ColorExtensions.cs
index 70f8bc0..239497d 100644
--- a/NesTiler/ColorExtensions.cs
+++ b/NesTiler/ColorExtensions.cs
@@ -14,7 +14,8 @@ namespace com.clusterrr.Famicom.NesTiler
 
     static class ColorExtensions
     {
-        static Dictionary<ColorPair, double> cache = new();
+        private static Dictionary<ColorPair, double> cache = new();
+        private static CieDe2000Comparison comparer = new();
 
         public static void ClearCache() => cache.Clear();
 
@@ -38,7 +39,7 @@ namespace com.clusterrr.Famicom.NesTiler
                 return cache[pair];
             var a = new Rgb { R = color1.Red, G = color1.Green, B = color1.Blue };
             var b = new Rgb { R = color2.Red, G = color2.Green, B = color2.Blue };
-            var delta = a.Compare(b, new CieDe2000Comparison());
+            var delta = a.Compare(b, comparer);
             cache[pair] = delta;
             return delta;
         }
diff --git a/NesTiler/FastBitmap.cs b/NesTiler/FastBitmap.cs
index 1015354..5831170 100644
--- a/NesTiler/FastBitmap.cs
+++ b/NesTiler/FastBitmap.cs
@@ -11,27 +11,32 @@ namespace com.clusterrr.Famicom.NesTiler
         public int Width { get; }
         public int Height { get; }
 
-        private readonly SKColor[] colors;
-        private static Dictionary<string, SKBitmap> imagesCache = new Dictionary<string, SKBitmap>();
+        private readonly int verticalOffset;
+        private readonly SKColor[] pixels;
+        private static Dictionary<string, (SKColor[] pixels, int w, int h)> imagesCache = new();
 
-        private FastBitmap(SKBitmap skBitmap, int verticalOffset = 0, int height = -1)
+        private FastBitmap(SKColor[] pixels, int originalWidth, int originalHeight, int verticalOffset = 0, int height = -1)
         {
-            Width = skBitmap.Width;
-            Height = height <= 0 ? skBitmap.Height - verticalOffset : height;
-            if (skBitmap.Height - verticalOffset - Height < 0 || Height <= 0) throw new InvalidOperationException("Invalid image height.");
-            var pixels = skBitmap.Pixels;
-            colors = skBitmap.Pixels.Skip(verticalOffset * Width).Take(Width * Height).ToArray();
+            Width = originalWidth;
+            Height = height <= 0 ? originalHeight - verticalOffset : height;
+            this.verticalOffset = verticalOffset;
+            this.pixels = pixels;
         }
 
         public static FastBitmap? Decode(string filename, int verticalOffset = 0, int height = -1)
         {
+            if (imagesCache.TryGetValue(filename, out (SKColor[] pixels, int w, int h) cachedImage))
+            {
+                return new FastBitmap(cachedImage.pixels, cachedImage.w, cachedImage.h, verticalOffset, height);
+            }
             try
             {
                 using (var image = SKBitmap.Decode(filename))
                 {
                     if (image == null) return null;
-                    imagesCache[filename] = image;
-                    return new FastBitmap(image, verticalOffset, height);
+                    var pixels = image.Pixels;
+                    imagesCache[filename] = (pixels, image.Width, image.Height);
+                    return new FastBitmap(pixels, image.Width, image.Height, verticalOffset, height);
                 }
             }
             finally
@@ -42,12 +47,12 @@ namespace com.clusterrr.Famicom.NesTiler
 
         public SKColor GetPixelColor(int x, int y)
         {
-            return colors[(y * Width) + x];
+            return pixels[((y + verticalOffset) * Width) + x];
         }
 
         public void SetPixelColor(int x, int y, SKColor color)
         {
-            colors[(y * Width) + x] = color;
+            pixels[((y + verticalOffset) * Width) + x] = color;
         }
 
         public byte[] Encode(SKEncodedImageFormat format, int v)
@@ -57,7 +62,7 @@ namespace com.clusterrr.Famicom.NesTiler
             {
                 for (int x = 0; x < Width; x++)
                 {
-                    var color = colors[(y * Width) + x];
+                    var color = GetPixelColor(x, y);
                     skImage.SetPixel(x, y, color);
                 }
             }
-- 
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