Now throws a better excpetion DrawImage source does not overlap target

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

@@ -71,7 +71,7 @@ protected override void OnFrameApply(ImageFrame<TPixelDst> source, Rectangle sou
             Rectangle bounds = targetImage.Bounds();
 
             int minX = Math.Max(this.Location.X, sourceRectangle.X);
-            int maxX = Math.Min(this.Location.X + bounds.Width, sourceRectangle.Width);
+            int maxX = Math.Min(this.Location.X + bounds.Width, sourceRectangle.Right);
             int targetX = minX - this.Location.X;
 
             int minY = Math.Max(this.Location.Y, sourceRectangle.Y);
@@ -81,6 +81,12 @@ protected override void OnFrameApply(ImageFrame<TPixelDst> source, Rectangle sou
 
             var workingRect = Rectangle.FromLTRB(minX, minY, maxX, maxY);
 
+            // not a valid operation because rectangle does not overlap with this image.
+            if (workingRect.Width <= 0 || workingRect.Height <= 0)
+            {
+                throw new ImageProcessingException("Cannot draw image because the source image does not overlap the target image.");
+            }
+
             ParallelHelper.IterateRows(
                 workingRect,
                 configuration,

src/ImageSharp/Common/ParallelUtils/ParallelHelper.cs

@@ -45,7 +45,7 @@ public static void IterateRows(
             in ParallelExecutionSettings parallelSettings,
             Action<RowInterval> body)
         {
-            DebugGuard.MustBeGreaterThan(rectangle.Width, 0, nameof(rectangle));
+            ValidateRectangle(rectangle);
 
             int maxSteps = DivideCeil(rectangle.Width * rectangle.Height, parallelSettings.MinimumPixelsProcessedPerTask);
 
@@ -87,6 +87,8 @@ public static void IterateRowsWithTempBuffer<T>(
             Action<RowInterval, Memory<T>> body)
             where T : unmanaged
         {
+            ValidateRectangle(rectangle);
+
             int maxSteps = DivideCeil(rectangle.Width * rectangle.Height, parallelSettings.MinimumPixelsProcessedPerTask);
 
             int numOfSteps = Math.Min(parallelSettings.MaxDegreeOfParallelism, maxSteps);
@@ -142,5 +144,18 @@ public static void IterateRowsWithTempBuffer<T>(
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static int DivideCeil(int dividend, int divisor) => 1 + ((dividend - 1) / divisor);
+
+        private static void ValidateRectangle(Rectangle rectangle)
+        {
+            Guard.MustBeGreaterThan(
+                rectangle.Width,
+                0,
+                $"{nameof(rectangle)}.{nameof(rectangle.Width)}");
+
+            Guard.MustBeGreaterThan(
+                rectangle.Height,
+                0,
+                $"{nameof(rectangle)}.{nameof(rectangle.Height)}");
+        }
     }
 }

tests/ImageSharp.Tests/Drawing/DrawImageTest.cs

@@ -131,6 +131,48 @@ public void ImageShouldHandlePositiveLocation(TestImageProvider<Rgba32> provider
                 background.DebugSave(provider, testOutputDetails: "Positive");
             }
         }
+        [Theory]
+        [WithSolidFilledImages(100, 100, 255, 255, 255, PixelTypes.Rgba32)]
+        public void ImageShouldHandlePositiveLocationTruncatedOverlay(TestImageProvider<Rgba32> provider)
+        {
+            using (Image<Rgba32> background = provider.GetImage())
+            using (var overlay = new Image<Rgba32>(50, 50))
+            {
+                overlay.Mutate(x => x.Fill(Rgba32.Black));
+
+                const int xy = 75;
+                Rgba32 backgroundPixel = background[xy - 1, xy - 1];
+                Rgba32 overlayPixel = overlay[0, 0];
+
+                background.Mutate(x => x.DrawImage(overlay, new Point(xy, xy), PixelColorBlendingMode.Normal, 1F));
+
+                Assert.Equal(Rgba32.White, backgroundPixel);
+                Assert.Equal(overlayPixel, background[xy, xy]);
+
+                background.DebugSave(provider, testOutputDetails: "PositiveTruncated");
+            }
+        }
+
+        [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 NonOverlappingImageThrows(TestImageProvider<Rgba32> provider, int x, int y)
+        {
+            using (Image<Rgba32> background = provider.GetImage())
+            using (var overlay = new Image<Rgba32>(Configuration.Default, 10, 10, Rgba32.Black))
+            {
+                ImageProcessingException ex = Assert.Throws<ImageProcessingException>(Test);
+
+                Assert.Contains("does not overlap", ex.ToString());
+
+                void Test()
+                {
+                    background.Mutate(context => context.DrawImage(overlay, new Point(x, y), GraphicsOptions.Default));
+                }
+            }
+        }
 
         private static void VerifyImage<TPixel>(
             TestImageProvider<TPixel> provider,

tests/ImageSharp.Tests/Helpers/ParallelHelperTests.cs

@@ -9,6 +9,7 @@
 
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.ParallelUtils;
+using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Memory;
 using SixLabors.Primitives;
 
@@ -334,5 +335,39 @@ 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);
+
+            ArgumentOutOfRangeException ex = Assert.Throws<ArgumentOutOfRangeException>(
+                () => ParallelHelper.IterateRows(rect, parallelSettings, (rows) => { }));
+
+            Assert.Contains(width <= 0 ? "Width" : "Height", ex.Message);
+        }
+
+        [Theory]
+        [InlineData(0, 10)]
+        [InlineData(10, 0)]
+        [InlineData(-10, 10)]
+        [InlineData(10, -10)]
+        public void IterateRowsWithTempBufferRequiresValidRectangle(int width, int height)
+        {
+            var parallelSettings = new ParallelExecutionSettings();
+
+            var rect = new Rectangle(0, 0, width, height);
+
+            ArgumentOutOfRangeException ex = Assert.Throws<ArgumentOutOfRangeException>(
+                () => ParallelHelper.IterateRowsWithTempBuffer<Rgba32>(rect, parallelSettings, (rows, memory) => { }));
+
+            Assert.Contains(width <= 0 ? "Width" : "Height", ex.Message);
+        }
     }
 }