collage-maker/collage/collage.go

// Package collage makes a pic collage
package collage

import (
	"errors"
	"image"
	"image/color"
	"image/draw"
	"image/jpeg"
	"io"
	"io/fs"

	"go.oneofone.dev/resize"
)

type Dimension struct {
	Width  uint `json:"width"`
	Height uint `json:"height"`
}

type Point struct {
	X uint `json:"x"`
	Y uint `json:"y"`
}

type Rectangle struct {
	Start Point `json:"start"`
	End   Point `json:"end"`
}

func (r Rectangle) ToImgRect() image.Rectangle {
	return image.Rectangle{
		Min: image.Point{int(r.Start.X), int(r.Start.Y)},
		Max: image.Point{int(r.End.X), int(r.End.Y)},
	}
}

type Photo struct {
	ImageName string    `json:"image"`
	Crop      Rectangle `json:"crop"`
	Frame     Rectangle `json:"frame"`
}

type Request struct {
	BackgroundImage string    `json:"background_image"`
	Aspect          Dimension `json:"aspect"`
	Dimension       Dimension `json:"dimension"`
	Photos          []Photo   `json:"photos"`
}

func Make(req Request, source fs.FS, output io.Writer) error {
	rec := image.Rect(0, 0, int(req.Aspect.Width), int(req.Aspect.Height))
	canvas := image.NewRGBA64(rec)
	white := color.RGBA{255, 255, 255, 255}
	draw.Draw(canvas, rec, &image.Uniform{white}, image.Point{}, draw.Src)
	for _, photo := range req.Photos {
		img, err := GetImage(source, photo.ImageName)
		if err != nil {
			return err
		}
		croppedImage, err := Crop(img, photo.Crop)
		if err != nil {
			return err
		}

		destRect := FrameTranslate(req.Aspect, req.Dimension, photo.Frame).ToImgRect()
		resizedImg := resize.Resize(uint(destRect.Dx()), uint(destRect.Dy()), croppedImage, resize.Lanczos3)
		draw.Draw(canvas, destRect, resizedImg, image.Point{0, 0}, draw.Src)
	}
	var opt jpeg.Options
	opt.Quality = 100

	return jpeg.Encode(output, canvas, &opt)
}

func FrameTranslate(resolution Dimension, frameSize Dimension, frame Rectangle) Rectangle {
	newX := func(oldX uint) uint {
		return oldX * resolution.Width / frameSize.Width
	}
	newY := func(oldY uint) uint {
		return oldY * resolution.Height / frameSize.Height
	}
	return Rectangle{
		Start: Point{newX(frame.Start.X), newY(frame.Start.Y)},
		End:   Point{newX(frame.End.X), newY(frame.End.Y)},
	}
}

type HasSubImage interface {
	SubImage(r image.Rectangle) image.Image
}

func Crop(img image.Image, r Rectangle) (image.Image, error) {
	if imgHS, ok := img.(HasSubImage); ok {
		return imgHS.SubImage(r.ToImgRect()), nil
	}
	return nil, errors.New("image does not support cropping")
}

func GetImage(source fs.FS, imageName string) (image.Image, error) {
	imgF, err := source.Open(imageName)
	if err != nil {
		return nil, err
	}
	img, _, err := image.Decode(imgF)
	return img, err
}