CheckDimensions

src/ImageSharp/Formats/Jpg/Utils/JpegUtils.cs

@@ -13,12 +13,9 @@ namespace ImageSharp.Formats.Jpg
     internal static unsafe class JpegUtils
     {
         /// <summary>
-        /// Copy a region of an image into dest. De "outlier" area will be stretched out with pixels on the right and bottom of
-        ///     the image.
+        /// Copy a region of an image into dest. De "outlier" area will be stretched out with pixels on the right and bottom of the image.
         /// </summary>
-        /// <typeparam name="TColor">
-        /// The pixel type
-        /// </typeparam>
+        /// <typeparam name="TColor">The pixel type</typeparam>
         /// <param name="pixels">The input pixel acessor</param>
         /// <param name="dest">The destination <see cref="PixelArea{TColor}"/></param>
         /// <param name="sourceY">Starting Y coord</param>
@@ -30,27 +27,57 @@ namespace ImageSharp.Formats.Jpg
             int sourceX)
             where TColor : struct, IPackedPixel, IEquatable<TColor>
         {
-            pixels.CopyTo(dest, sourceY, sourceX);
+            pixels.UncheckedCopyTo(dest, sourceY, sourceX);
             int stretchFromX = pixels.Width - sourceX;
             int stretchFromY = pixels.Height - sourceY;
             StretchPixels(dest, stretchFromX, stretchFromY);
         }
 
+        /// <summary>
+        /// Copy a region of image into the image destination area. Does not throw when requesting a 0-size copy.
+        /// </summary>
+        /// <typeparam name="TColor">The pixel type</typeparam>
+        /// <param name="sourcePixels">The source <see cref="PixelAccessor{TColor}"/> </param>
+        /// <param name="destinationArea">The destination area.</param>
+        /// <param name="sourceY">The source row index.</param>
+        /// <param name="sourceX">The source column index.</param>
+        /// <exception cref="NotSupportedException">
+        /// Thrown when an unsupported component order value is passed.
+        /// </exception>
+        public static void UncheckedCopyTo<TColor>(
+            this PixelAccessor<TColor> sourcePixels,
+            PixelArea<TColor> destinationArea,
+            int sourceY,
+            int sourceX)
+            where TColor : struct, IPackedPixel, IEquatable<TColor>
+        {
+            // TODO: Code smell! This is exactly the same code PixelArea<TColor>.CopyTo() starts with!
+            int width = Math.Min(destinationArea.Width, sourcePixels.Width - sourceX);
+            int height = Math.Min(destinationArea.Height, sourcePixels.Height - sourceY);
+            if (width < 1 || height < 1)
+            {
+                return;
+            }
+
+            sourcePixels.CopyTo(destinationArea, sourceY, sourceX);
+        }
+
         /// <summary>
         /// Copy an RGB value
         /// </summary>
         /// <param name="source">Source pointer</param>
         /// <param name="dest">Destination pointer</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal static void CopyRgb(byte* source, byte* dest)
+        public static void CopyRgb(byte* source, byte* dest)
         {
             *dest++ = *source++; // R
             *dest++ = *source++; // G
             *dest = *source; // B
         }
 
+        // Nothing to stretch if (fromX, fromY) is outside the area, or is at (0,0)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static bool IsInvalidStretchArea<TColor>(PixelArea<TColor> area, int fromX, int fromY)
+        private static bool IsInvalidStretchStartingPosition<TColor>(PixelArea<TColor> area, int fromX, int fromY)
             where TColor : struct, IPackedPixel, IEquatable<TColor>
         {
             return fromX <= 0 || fromY <= 0 || fromX >= area.Width || fromY >= area.Height;
@@ -59,7 +86,7 @@ namespace ImageSharp.Formats.Jpg
         private static void StretchPixels<TColor>(PixelArea<TColor> area, int fromX, int fromY)
             where TColor : struct, IPackedPixel, IEquatable<TColor>
         {
-            if (IsInvalidStretchArea(area, fromX, fromY))
+            if (IsInvalidStretchStartingPosition(area, fromX, fromY))
             {
                 return;
             }

src/ImageSharp/Image/PixelAccessor{TColor}.cs

@@ -186,7 +186,7 @@ namespace ImageSharp
             int width = Math.Min(area.Width, this.Width - targetX);
             int height = Math.Min(area.Height, this.Height - targetY);
 
-            // this.CheckDimensions(width, height); TODO: Why was width == 0 or height == 0 considered a problem? Copy implementations do not fail on this (just do nothing)!
+            this.CheckDimensions(width, height);
             switch (area.ComponentOrder)
             {
                 case ComponentOrder.ZYX:
@@ -220,7 +220,7 @@ namespace ImageSharp
             int width = Math.Min(area.Width, this.Width - sourceX);
             int height = Math.Min(area.Height, this.Height - sourceY);
 
-            // this.CheckDimensions(width, height); TODO: Why was width == 0 or height == 0 considered a problem? Copy implementations do not fail on this (just do nothing)!
+            this.CheckDimensions(width, height);
             switch (area.ComponentOrder)
             {
                 case ComponentOrder.ZYX: