How to rotate an image by a certain angle in Go?

To rotate an image by a certain angle in Go, you can use the golang.org/x/image/draw package. Follow the steps below:

Import the necessary packages:

import (
    "image"
    "image/draw"
    "golang.org/x/image/math/fixed"
    "golang.org/x/image/vector"
)

Create a new draw.Image from the original image:

originalImg, _ := // load the original image
originalBounds := originalImg.Bounds()
rotatedImg := image.NewRGBA(originalBounds)

Create a draw.Context using the rotatedImg:

rotatedCtx := draw.NewContext(rotatedImg, originalBounds)

Define the rotation angle in radians:

angle := // specify the angle in radians

Calculate the center point of the original image:

center := fixed.Point26_6{
    X: fixed.Int26_6(originalBounds.Dx() / 2),
    Y: fixed.Int26_6(originalBounds.Dy() / 2),
}

Use a vector.Affine2D to rotate the image:

matrix := vector.NewMatrix()
matrix = matrix.Translate(center.X, center.Y)
matrix = matrix.Rotate(angle)
matrix = matrix.Translate(-center.X, -center.Y)
rotatedCtx.SetTransform(matrix)

Draw the rotated image onto the rotatedCtx:

rotatedCtx.DrawImage(originalBounds, originalImg, originalBounds.Min, draw.Src)

Use the rotatedImg as the output image.

Here's an example of how you can rotate an image by 45 degrees:

package main

import (
	"image"
	"image/draw"
	"log"
	"os"

	"golang.org/x/image/math/fixed"
	"golang.org/x/image/vector"
)

func main() {
	// Load the original image
	file, err := os.Open("input.png")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	originalImg, _, err := image.Decode(file)
	if err != nil {
		log.Fatal(err)
	}

	originalBounds := originalImg.Bounds()
	rotatedImg := image.NewRGBA(originalBounds)
	rotatedCtx := draw.NewContext(rotatedImg, originalBounds)

	angle := 45.0 * (3.14159 / 180.0) // Convert degrees to radians

	center := fixed.Point26_6{
		X: fixed.Int26_6(originalBounds.Dx() / 2),
		Y: fixed.Int26_6(originalBounds.Dy() / 2),
	}

	matrix := vector.NewMatrix()
	matrix = matrix.Translate(center.X, center.Y)
	matrix = matrix.Rotate(angle)
	matrix = matrix.Translate(-center.X, -center.Y)
	rotatedCtx.SetTransform(matrix)

	rotatedCtx.DrawImage(originalBounds, originalImg, originalBounds.Min, draw.Src)

	// Save the rotated image
	outFile, err := os.Create("output.png")
	if err != nil {
		log.Fatal(err)
	}
	defer outFile.Close()

	err = png.Encode(outFile, rotatedImg)
	if err != nil {
		log.Fatal(err)
	}
}

Make sure to replace "input.png" with the path to your input image, and "output.png" with the desired path for the output image.