Now throws a better excpetion DrawImage source does not overlap target

src/ImageSharp.Drawing/Processing/Processors/Drawing/DrawImageProcessor.cs

@@ -81,6 +81,12 @@ protected override void OnFrameApply(ImageFrame<TPixelDst> source, Rectangle sou
 
             var workingRect = Rectangle.FromLTRB(minX, minY, maxX, maxY);
 
+            if (workingRect.Width < 0 || workingRect.Height < 0)
+            {
+                // no effect because rectangle does not overlap with this image.
+                return;
+            }
+
             ParallelHelper.IterateRows(
                 workingRect,
                 configuration,

src/ImageSharp/Common/ParallelUtils/ParallelHelper.cs

@@ -45,7 +45,8 @@ public static void IterateRows(
             in ParallelExecutionSettings parallelSettings,
             Action<RowInterval> body)
         {
-            DebugGuard.MustBeGreaterThan(rectangle.Width, 0, nameof(rectangle));
+            Guard.MustBeGreaterThan(rectangle.Width, 0, nameof(rectangle));
+            Guard.MustBeGreaterThan(rectangle.Height, 0, nameof(rectangle));
 
             int maxSteps = DivideCeil(rectangle.Width * rectangle.Height, parallelSettings.MinimumPixelsProcessedPerTask);
 

tests/ImageSharp.Tests/Drawing/DrawImageTest.cs

@@ -132,6 +132,26 @@ public void ImageShouldHandlePositiveLocation(TestImageProvider<Rgba32> provider
             }
         }
 
+        [Theory]
+        [WithSolidFilledImages(100, 100, 255, 255, 255, PixelTypes.Rgba32, -30, -30)]
+        [WithSolidFilledImages(100, 100, 255, 255, 255, PixelTypes.Rgba32, 130, -30)]
+        [WithSolidFilledImages(100, 100, 255, 255, 255, PixelTypes.Rgba32, 130, 130)]
+        [WithSolidFilledImages(100, 100, 255, 255, 255, PixelTypes.Rgba32, -30, 130)]
+        public void NonOverlappingImageHasNoEffect(TestImageProvider<Rgba32> provider, int x, int y)
+        {
+            using (Image<Rgba32> original = provider.GetImage())
+            using (Image<Rgba32> background = provider.GetImage())
+            using (var overlay = new Image<Rgba32>(Configuration.Default, 10, 10, Rgba32.Black))
+            {
+                background.Mutate(context => context.DrawImage(overlay, new Point(x, y), GraphicsOptions.Default));
+
+                // background image should be unmodified
+                ImageComparer.Exact.CompareImagesOrFrames(original, background);
+
+                background.DebugSave(provider, testOutputDetails: "NonOverlapping");
+            }
+        }
+
         private static void VerifyImage<TPixel>(
             TestImageProvider<TPixel> provider,
             PixelColorBlendingMode mode,

tests/ImageSharp.Tests/Helpers/ParallelHelperTests.cs

@@ -334,5 +334,20 @@ void FillRow(int y, Buffer2D<Point> buffer)
                 TestImageExtensions.CompareBuffers(expected.Span, actual.Span);
             }
         }
+
+        [Theory]
+        [InlineData(0, 10)]
+        [InlineData(10, 0)]
+        [InlineData(-10, 10)]
+        [InlineData(10, -10)]
+        public void IterateRowsRequiresValidRectangle(int width, int height)
+        {
+            var parallelSettings = new ParallelExecutionSettings();
+
+            var rect = new Rectangle(0, 0, width, height);
+
+            Assert.Throws<ArgumentOutOfRangeException>(
+                () => { ParallelHelper.IterateRows(rect, parallelSettings, (rows) => { }); });
+        }
     }
 }