[DW-34] fix GetRGBABuffer and add TestGetRGBABuffer

Author: ikkyuland

IronSoftware.Drawing/IronSoftware.Drawing.Common.Tests/UnitTests/AnyBitmapFunctionality.cs

@@ -798,6 +798,25 @@ public void TestGetRGBBuffer()
             Assert.Equal(firstPixel.B, buffer[2]);
         }
 
+        [FactWithAutomaticDisplayName]
+        public void TestGetRGBABuffer()
+        {
+            string imagePath = GetRelativeFilePath("checkmark.jpg");
+            using var bitmap = new AnyBitmap(imagePath);
+            var expectedSize = bitmap.Width * bitmap.Height * 4; // 3 bytes per pixel (RGB)
+
+            byte[] buffer = bitmap.GetRGBABuffer();
+
+            Assert.Equal(expectedSize, buffer.Length);
+
+            // Verify the first pixel's RGB values
+            var firstPixel = bitmap.GetPixel(0, 0);
+            Assert.Equal(firstPixel.R, buffer[0]);
+            Assert.Equal(firstPixel.G, buffer[1]);
+            Assert.Equal(firstPixel.B, buffer[2]);
+            Assert.Equal(firstPixel.A, buffer[3]);
+        }
+
         [FactWithAutomaticDisplayName]
         public void Test_LoadFromRGBBuffer()
         {

IronSoftware.Drawing/IronSoftware.Drawing.Common/AnyBitmap.cs

@@ -1625,7 +1625,7 @@ public byte[] GetRGBABuffer()
             var image = _lazyImage.Value.First();
             int width = image.Width;
             int height = image.Height;
-            byte[] rgbBuffer = new byte[width * height * 3]; // 3 bytes per pixel (RGB)
+            byte[] rgbBuffer = new byte[width * height * 4]; // 3 bytes per pixel (RGB)
             switch (image)
             {
                 case Image<Rgba32> imageAsFormat: