Fix ImageSlice.cgImage which contains the last row of the original image

Author: koher

Sources/EasyImagy/ImageSlice.swift

@@ -56,13 +56,24 @@ extension ImageSlice { // Gray or PremultipliedRGBA
         bitmapInfo: CGBitmapInfo,
         componentType: Component.Type
     ) -> CGImage {
-        let length = slice.image.width * slice.height * MemoryLayout<Pixel>.size
+        let imageCount = slice.image.count
+        let pixelCount = slice.image.width * slice.height
+        let length = pixelCount * MemoryLayout<Pixel>.size
+        let offset = slice.yRange.lowerBound * slice.image.width + slice.xRange.lowerBound
 
-        let bytes: UnsafeMutablePointer<Pixel> = UnsafeMutablePointer(mutating: slice.image.pixels) + (slice.yRange.lowerBound * slice.image.width + slice.xRange.lowerBound)
-        let provider: CGDataProvider = CGDataProvider(data: Data(
-            bytes: bytes,
-            count: length
-        ) as CFData)!
+        var data: Data
+        if offset + pixelCount <= imageCount {
+            let bytes: UnsafeMutablePointer<Pixel> = UnsafeMutablePointer(mutating: slice.image.pixels) + (slice.yRange.lowerBound * slice.image.width + slice.xRange.lowerBound)
+            data = Data(bytes: bytes, count: length)
+        } else {
+            let bytes: UnsafeMutablePointer<Pixel> = UnsafeMutablePointer(mutating: slice.image.pixels) + (slice.yRange.lowerBound * slice.image.width + slice.xRange.lowerBound)
+            let pointer: UnsafeMutablePointer<UInt8> = UnsafeMutableRawPointer(bytes).bindMemory(to: UInt8.self, capacity: length)
+            data = Data(capacity: pixelCount * MemoryLayout<Pixel>.size)
+            data.append(pointer, count: (imageCount - offset) * MemoryLayout<Pixel>.size)
+            data.append(pointer, count: (offset + pixelCount - imageCount) * MemoryLayout<Pixel>.size)
+        }
+        
+        let provider: CGDataProvider = CGDataProvider(data: data as CFData)!
 
         return CGImage(
             width: slice.width,

Tests/EasyImagyTests/ImageCoreGraphicsTest.swift

@@ -201,6 +201,46 @@ import EasyImagy
                 XCTAssertEqual(restored[0, 0], PremultipliedRGBA<UInt8>(red: 24, green: 49, blue: 99, alpha: 127))
                 XCTAssertEqual(restored[0, 1], PremultipliedRGBA<UInt8>(red: 1, green: 2, blue: 3, alpha: 4))
             }
+            
+            do { // slices which contains the last row of the original images
+                let slice: ImageSlice<UInt8> = Image<UInt8>(width: 4, height: 3, pixels: [
+                    0, 0, 0, 0,
+                    0, 1, 2, 3,
+                    0, 4, 5, 6,
+                ])[1...3, 1...2]
+                
+                let cgImage = slice.cgImage
+                let restored = Image<UInt8>(cgImage: cgImage)
+                
+                XCTAssertEqual(restored.width, 3)
+                XCTAssertEqual(restored.height, 2)
+                
+                XCTAssertEqual(restored[0, 0], 1)
+                XCTAssertEqual(restored[1, 0], 2)
+                XCTAssertEqual(restored[2, 0], 3)
+                
+                XCTAssertEqual(restored[0, 1], 4)
+                XCTAssertEqual(restored[1, 1], 5)
+                XCTAssertEqual(restored[2, 1], 6)
+            }
+            
+            do { // slices which contains the last row of the original images
+                let transparent = PremultipliedRGBA<UInt8>(red: 0, green: 0, blue: 0, alpha: 0)
+                let slice: ImageSlice<PremultipliedRGBA<UInt8>> = Image<PremultipliedRGBA<UInt8>>(width: 2, height: 3, pixels: [
+                    transparent, transparent,
+                    transparent, PremultipliedRGBA<UInt8>(red: 24, green: 49, blue: 99, alpha: 127),
+                    transparent, PremultipliedRGBA<UInt8>(red: 1, green: 2, blue: 3, alpha: 4),
+                ])[1...1, 1...2]
+                
+                let cgImage = slice.cgImage
+                let restored = Image<PremultipliedRGBA<UInt8>>(cgImage: cgImage)
+                
+                XCTAssertEqual(restored.width, 1)
+                XCTAssertEqual(restored.height, 2)
+                
+                XCTAssertEqual(restored[0, 0], PremultipliedRGBA<UInt8>(red: 24, green: 49, blue: 99, alpha: 127))
+                XCTAssertEqual(restored[0, 1], PremultipliedRGBA<UInt8>(red: 1, green: 2, blue: 3, alpha: 4))
+            }
         }
 
         func testWithCGImage() {