From 7ce2543be63caed3a3f16c4565de65563a2c9494 Mon Sep 17 00:00:00 2001
From: Peter <peter.dyumin@gmail.com>
Date: Sat, 14 Jan 2023 23:36:44 +0300
Subject: [PATCH 1/2] Fix horizontal and vertical flipping

---
 processing/flip-horizontal.go | 6 +++++-
 processing/flip-vertical.go   | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/processing/flip-horizontal.go b/processing/flip-horizontal.go
index 6464129..7222897 100644
--- a/processing/flip-horizontal.go
+++ b/processing/flip-horizontal.go
@@ -9,7 +9,11 @@ import (
 func FlipHorizontal(source [][]color.Color) [][]color.Color {
 	width, height := len(source), len(source[0])
 	destination := utilities.CreateGrid(width, height)
-	for x := 0; x < width/2; x += 1 {
+	correction := 0
+	if width%2 != 0 {
+		correction = 1
+	}
+	for x := 0; x < width/2+correction; x += 1 {
 		for y := 0; y < height; y += 1 {
 			z := width - x - 1
 			destination[x][y], destination[z][y] = source[z][y], source[x][y]
diff --git a/processing/flip-vertical.go b/processing/flip-vertical.go
index 7dde204..932ef91 100644
--- a/processing/flip-vertical.go
+++ b/processing/flip-vertical.go
@@ -9,8 +9,12 @@ import (
 func FlipVertical(source [][]color.Color) [][]color.Color {
 	width, height := len(source), len(source[0])
 	destination := utilities.CreateGrid(width, height)
+	correction := 0
+	if height%2 != 0 {
+		correction = 1
+	}
 	for x := 0; x < width; x += 1 {
-		for y := 0; y < height/2; y += 1 {
+		for y := 0; y < height/2+correction; y += 1 {
 			z := height - y - 1
 			destination[x][y], destination[x][z] = source[x][z], source[x][y]
 		}

From 1771718682836061524f949ebb7828a92273a066 Mon Sep 17 00:00:00 2001
From: Peter <peter.dyumin@gmail.com>
Date: Sat, 14 Jan 2023 23:46:56 +0300
Subject: [PATCH 2/2] Add hue rotation filter

---
 README.md                |  6 +++++
 index.go                 | 17 ++++++++++++++
 processing/hue-rotate.go | 49 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)
 create mode 100644 processing/hue-rotate.go

diff --git a/README.md b/README.md
index e1580b0..2660cd9 100644
--- a/README.md
+++ b/README.md
@@ -179,6 +179,12 @@ func controller(context *fiber.Ctx) error {
   )
   ```
 
+- **Hue rotation**: rotate image hue to change the colors. Requires an angle to be provided. Angle represents degree of a hue rotation, can be any `int` number:
+
+  ```golang
+  rotated, format, processingError := brille.HueRotate(file, 278)
+  ```
+
 - **Laplasian filter**: a static edge detection filter that uses a 3x3 kernel. It can be used to outline edges on an image:
 
   ```golang
diff --git a/index.go b/index.go
index b692792..3388b03 100644
--- a/index.go
+++ b/index.go
@@ -203,6 +203,23 @@ func Grayscale(file io.Reader, grayscaleType string) (io.Reader, string, error)
 	return encoded, format, nil
 }
 
+// angle: any int value
+func HueRotate(file io.Reader, angle int) (io.Reader, string, error) {
+	if file == nil {
+		return nil, "", errors.New(constants.ERROR_NO_FILE_PROVIDED)
+	}
+	source, format, preparationError := utilities.PrepareSource(file)
+	if preparationError != nil {
+		return nil, "", preparationError
+	}
+	rotated := processing.HueRotate(source, angle)
+	encoded, encodingError := utilities.PrepareResult(rotated, format)
+	if encodingError != nil {
+		return nil, "", encodingError
+	}
+	return encoded, format, nil
+}
+
 func LaplasianFilter(file io.Reader) (io.Reader, string, error) {
 	if file == nil {
 		return nil, "", errors.New(constants.ERROR_NO_FILE_PROVIDED)
diff --git a/processing/hue-rotate.go b/processing/hue-rotate.go
new file mode 100644
index 0000000..490ae24
--- /dev/null
+++ b/processing/hue-rotate.go
@@ -0,0 +1,49 @@
+package processing
+
+import (
+	"image/color"
+	"math"
+
+	"github.com/julyskies/brille/utilities"
+)
+
+const DEG float64 = math.Pi / 180
+
+func HueRotate(source [][]color.Color, angle int) [][]color.Color {
+	width, height := len(source), len(source[0])
+	destination := utilities.CreateGrid(width, height)
+	cos := math.Cos(float64(angle) * DEG)
+	sin := math.Sin(float64(angle) * DEG)
+	matrix := [3]float64{
+		cos + (1-cos)/3,
+		(1-cos)/3 - math.Sqrt(float64(1)/3)*sin,
+		(1-cos)/3 + math.Sqrt(float64(1)/3)*sin,
+	}
+	for x := 0; x < width; x += 1 {
+		for y := 0; y < height; y += 1 {
+			r, g, b, alpha := utilities.RGBA(source[x][y])
+			rr := utilities.MaxMin(
+				float64(r)*matrix[0]+float64(g)*matrix[1]+float64(b)*matrix[2],
+				255,
+				0,
+			)
+			rg := utilities.MaxMin(
+				float64(r)*matrix[2]+float64(g)*matrix[0]+float64(b)*matrix[1],
+				255,
+				0,
+			)
+			rb := utilities.MaxMin(
+				float64(r)*matrix[1]+float64(g)*matrix[2]+float64(b)*matrix[0],
+				255,
+				0,
+			)
+			destination[x][y] = color.RGBA{
+				uint8(rr),
+				uint8(rg),
+				uint8(rb),
+				alpha,
+			}
+		}
+	}
+	return destination
+}