Properly copy bitmaps. Fixes #497

binding/Binding/SKBitmap.cs

@@ -210,9 +210,6 @@ namespace SkiaSharp
 
 		public bool CopyTo (SKBitmap destination, SKColorType colorType)
 		{
-			// TODO: instead of working on `destination` directly, we should
-			//       create a temporary bitmap and then inject the data
-
 			if (destination == null) {
 				throw new ArgumentNullException (nameof (destination));
 			}
@@ -248,8 +245,10 @@ namespace SkiaSharp
 					break;
 			}
 
-			destination.Reset (); // TODO: is this needed?
+			// TODO: handle copying two Index8 images - copy/reference the color tables
-			if (!destination.TryAllocPixels (dstInfo, colorType == SKColorType.Index8 ? ColorTable : null)) {
+
+			var tmpDst = new SKBitmap ();
+			if (!tmpDst.TryAllocPixels (dstInfo, colorType == SKColorType.Index8 ? ColorTable : null)) {
 				return false;
 			}
 
@@ -274,6 +273,8 @@ namespace SkiaSharp
 				return false;
 			}
 
+			destination.Swap (tmpDst);
+
 			return true;
 		}
 
@@ -729,6 +730,11 @@ namespace SkiaSharp
 				return PeekPixels (pixmap) && pixmap.Encode (dst, format, quality);
 			}
 		}
+		
+		private void Swap (SKBitmap other)
+		{
+			SkiaApi.sk_bitmap_swap (Handle, other.Handle);
+		}
 
 		private static SKStream WrapManagedStream (Stream stream)
 		{

binding/Binding/SkiaApi.cs

@@ -1366,6 +1366,9 @@ namespace SkiaSharp
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
 		public extern static void sk_bitmap_notify_pixels_changed(sk_bitmap_t cbitmap);
 
+		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
+		public extern static void sk_bitmap_swap(sk_bitmap_t cbitmap, sk_bitmap_t cother);
+
 		// SKColor
 
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]

externals/skia

@@ -1 +1 @@
-Subproject commit 864434895d0487be35d1435ada049870d8664203
+Subproject commit ceff8e6562f6909837741b7798cd8727c10cf8e6

tests/Tests/SKBitmapTest.cs

@@ -25,6 +25,30 @@ namespace SkiaSharp.Tests
 			Assert.False(bmp.CanCopyTo(SKColorType.Gray8));
 		}
 
+		[SkippableFact]
+		public void CopyIndex8ToPlatformPreservesData()
+		{
+			var path = Path.Combine(PathToImages, "index8.png");
+			var bmp = SKBitmap.Decode(path);
+
+			var platform = bmp.Copy(SKImageInfo.PlatformColorType);
+
+			Assert.Equal((SKColor)0x7EA4C639, platform.GetPixel(182, 348));
+			Assert.Equal(SKImageInfo.PlatformColorType, platform.ColorType);
+		}
+
+		[SkippableFact]
+		public void OverwriteIndex8ToPlatformPreservesData()
+		{
+			var path = Path.Combine(PathToImages, "index8.png");
+			var bmp = SKBitmap.Decode(path);
+
+			bmp.CopyTo(bmp, SKImageInfo.PlatformColorType);
+
+			Assert.Equal((SKColor)0x7EA4C639, bmp.GetPixel(182, 348));
+			Assert.Equal(SKImageInfo.PlatformColorType, bmp.ColorType);
+		}
+
 		[SkippableFact]
 		public void BitmapCopyToAlpha8PreservesData()
 		{