Resize should respect source rectangle Fix #118

src/ImageSharp.Processing/Processors/Transforms/CompandingResizeProcessor.cs

@@ -56,6 +56,8 @@ namespace ImageSharp.Processing.Processors
 
             int width = this.Width;
             int height = this.Height;
+            int sourceX = sourceRectangle.X;
+            int sourceY = sourceRectangle.Y;
             int startY = this.ResizeRectangle.Y;
             int endY = this.ResizeRectangle.Bottom;
             int startX = this.ResizeRectangle.X;
@@ -83,12 +85,12 @@ namespace ImageSharp.Processing.Processors
                             y =>
                             {
                                 // Y coordinates of source points
-                                int originY = (int)((y - startY) * heightFactor);
+                                int originY = (int)(((y - startY) * heightFactor) + sourceY);
 
                                 for (int x = minX; x < maxX; x++)
                                 {
                                     // X coordinates of source points
-                                    targetPixels[x, y] = sourcePixels[(int)((x - startX) * widthFactor), originY];
+                                    targetPixels[x, y] = sourcePixels[(int)(((x - startX) * widthFactor) + sourceX), originY];
                                 }
                             });
                     }
@@ -110,7 +112,7 @@ namespace ImageSharp.Processing.Processors
                 {
                     Parallel.For(
                         0,
-                        sourceRectangle.Height,
+                        sourceRectangle.Bottom,
                         this.ParallelOptions,
                         y =>
                         {
@@ -125,7 +127,7 @@ namespace ImageSharp.Processing.Processors
                                 for (int i = 0; i < horizontalValues.Length; i++)
                                 {
                                     Weight xw = horizontalValues[i];
-                                    destination += sourcePixels[xw.Index, y].ToVector4().Expand() * xw.Value;
+                                    destination += sourcePixels[xw.Index + sourceX, y].ToVector4().Expand() * xw.Value;
                                 }
 
                                 TColor d = default(TColor);
@@ -152,7 +154,7 @@ namespace ImageSharp.Processing.Processors
                                 for (int i = 0; i < verticalValues.Length; i++)
                                 {
                                     Weight yw = verticalValues[i];
-                                    destination += firstPassPixels[x, yw.Index].ToVector4().Expand() * yw.Value;
+                                    destination += firstPassPixels[x, yw.Index + sourceY].ToVector4().Expand() * yw.Value;
                                 }
 
                                 TColor d = default(TColor);

src/ImageSharp.Processing/Processors/Transforms/ResizeProcessor.cs

@@ -55,6 +55,8 @@ namespace ImageSharp.Processing.Processors
 
             int width = this.Width;
             int height = this.Height;
+            int sourceX = sourceRectangle.X;
+            int sourceY = sourceRectangle.Y;
             int startY = this.ResizeRectangle.Y;
             int endY = this.ResizeRectangle.Bottom;
             int startX = this.ResizeRectangle.X;
@@ -82,12 +84,12 @@ namespace ImageSharp.Processing.Processors
                             y =>
                             {
                                 // Y coordinates of source points
-                                int originY = (int)((y - startY) * heightFactor);
+                                int originY = (int)(((y - startY) * heightFactor) + sourceY);
 
                                 for (int x = minX; x < maxX; x++)
                                 {
                                     // X coordinates of source points
-                                    targetPixels[x, y] = sourcePixels[(int)((x - startX) * widthFactor), originY];
+                                    targetPixels[x, y] = sourcePixels[(int)(((x - startX) * widthFactor) + sourceX), originY];
                                 }
                             });
                     }
@@ -109,7 +111,7 @@ namespace ImageSharp.Processing.Processors
                 {
                     Parallel.For(
                         0,
-                        sourceRectangle.Height,
+                        sourceRectangle.Bottom,
                         this.ParallelOptions,
                         y =>
                         {
@@ -124,7 +126,7 @@ namespace ImageSharp.Processing.Processors
                                 for (int i = 0; i < horizontalValues.Length; i++)
                                 {
                                     Weight xw = horizontalValues[i];
-                                    destination += sourcePixels[xw.Index, y].ToVector4() * xw.Value;
+                                    destination += sourcePixels[xw.Index + sourceX, y].ToVector4() * xw.Value;
                                 }
 
                                 TColor d = default(TColor);
@@ -151,7 +153,7 @@ namespace ImageSharp.Processing.Processors
                                 for (int i = 0; i < verticalValues.Length; i++)
                                 {
                                     Weight yw = verticalValues[i];
-                                    destination += firstPassPixels[x, yw.Index].ToVector4() * yw.Value;
+                                    destination += firstPassPixels[x, yw.Index + sourceY].ToVector4() * yw.Value;
                                 }
 
                                 TColor d = default(TColor);

tests/ImageSharp.Tests/Processors/Filters/ResizeTests.cs

@@ -50,6 +50,27 @@ namespace ImageSharp.Tests
             }
         }
 
+        [Theory]
+        [MemberData(nameof(ReSamplers))]
+        public void ImageShouldResizeFromSourceRectangle(string name, IResampler sampler)
+        {
+            name = $"{name}-SourceRect";
+
+            string path = this.CreateOutputDirectory("Resize");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName(name);
+                using (Image image = file.CreateImage())
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    var sourceRectangle = new Rectangle(image.Width / 8, image.Height / 8, image.Width / 4, image.Height / 4);
+                    var destRectangle = new Rectangle(image.Width / 4, image.Height / 4, image.Width / 2, image.Height / 2);
+                    image.Resize(image.Width, image.Height, sampler, sourceRectangle, destRectangle, false).Save(output);
+                }
+            }
+        }
+
         [Theory]
         [MemberData(nameof(ReSamplers))]
         public void ImageShouldResizeWidthAndKeepAspect(string name, IResampler sampler)