Demonstrate how to rotate and then crop image.

rotate_and_crop.go

// http://dev.pawelsz.eu/2016/04/go-imagick-image-croping-after-rotation.html
//
package main

import (
	"gopkg.in/gographics/imagick.v2/imagick"

	"log"
	"math"
)

func minUint(a, b uint) uint {
	if a < b {
		return a
	}
	return b
}

func calcSize(w, h uint) uint {
	return uint(math.Sqrt(2.) / 2. * float64(minUint(w, h)))
}

func main() {
	s := "example.jpeg"
	d := "example.cut.jpeg"

	iwand := imagick.NewMagickWand()
	defer iwand.Destroy()
	if err := iwand.ReadImage(s); err != nil {
		log.Panicf("cannot open image %s", err)
	}
	w := iwand.GetImageWidth()
	h := iwand.GetImageHeight()
	log.Printf("old size: %d,%d", w, h)
	pwand := imagick.NewPixelWand()
	pwand.SetColor("yellow")
	if err := iwand.RotateImage(pwand, 45); err != nil {
		log.Panicf("problem with rotation: %s", err)
	}

	newW := calcSize(w, h)
	newH := newW

	w = iwand.GetImageWidth()
	h = iwand.GetImageHeight()
	log.Printf("new size: %d,%d", w, h)

	x := int((w - newW) / 2)
	y := int((h - newH) / 2)
	// draw red rectangle around the area
	dwand := imagick.NewDrawingWand()
	pwand.SetColor("red")
	pwand.SetOpacity(0.5)
	dwand.SetFillColor(pwand)
	dwand.Rectangle(float64(x), float64(y), float64(newW+uint(x)), float64(newH+uint(y)))
	iwand.DrawImage(dwand)

	log.Printf("w,h,x,y: %d,%d,%d,%d", newW, newH, x, y)
	iwand.ResetImagePage("")
	if err := iwand.CropImage(newW, newH, x, y); err != nil {
		log.Fatalf("problem with crop: %s", err)
	}
	iwand.WriteImage(d)
}