thumbnail/scaler.go

package thumbnail

import (
	"bytes"
	"image"
	"image/jpeg"
	"image/png"

	"golang.org/x/image/bmp"
)

func (this *DirectThumbnailer) scaleImage(src image.Image) image.Image {
	srcW := src.Bounds().Max.X
	srcH := src.Bounds().Max.Y
	destW := 0
	destH := 0

	if srcW > srcH {
		destW = this.cfg.Width
		destH = this.cfg.Height * srcH / srcW
	} else {
		destW = this.cfg.Width * srcW / srcH
		destH = this.cfg.Height
	}

	offsetX := (this.cfg.Width - destW) / 2
	offsetY := (this.cfg.Height - destH) / 2

	scaleW := float64(srcW) / float64(destW)
	scaleH := float64(srcH) / float64(destH)

	dest := image.NewRGBA(image.Rectangle{Max: image.Point{X: this.cfg.Width, Y: this.cfg.Height}})

	switch this.cfg.Scale {

	case Bilinear:

		for y := 0; y < destH; y += 1 {
			for x := 0; x < destW; x += 1 {
				c00 := src.At(int(float64(x)*scaleW), int(float64(y)*scaleH))
				c01 := src.At(int((float64(x)+0.5)*scaleW), int(float64(y)*scaleH))
				c10 := src.At(int(float64(x)*scaleW), int((float64(y)+0.5)*scaleH))
				c11 := src.At(int((float64(x)+0.5)*scaleW), int((float64(y)+0.5)*scaleH))
				cBlend := Blend(Blend(c00, c01), Blend(c10, c11))
				dest.Set(x+offsetX, y+offsetY, cBlend)

			}
		}

	case NearestNeighbour:

		for y := 0; y < destH; y += 1 {
			for x := 0; x < destW; x += 1 {
				mapx := int(float64(x) * scaleW)
				mapy := int(float64(y) * scaleH)
				dest.Set(x+offsetX, y+offsetY, src.At(mapx, mapy))
			}
		}

	}

	return dest
}

func (this *DirectThumbnailer) encode(dest image.Image) ([]byte, error) {

	switch this.cfg.Output {
	case Png:
		buff := bytes.Buffer{}
		err := png.Encode(&buff, dest)
		if err != nil {
			return nil, err
		}
		return buff.Bytes(), nil

	case PngCrush:
		return crushFast(dest)

	case Jpeg:
		buff := bytes.Buffer{}
		err := jpeg.Encode(&buff, dest, &jpeg.Options{Quality: jpeg.DefaultQuality})
		if err != nil {
			return nil, err
		}

		return buff.Bytes(), nil

	case Bmp:
		buff := bytes.Buffer{}
		err := bmp.Encode(&buff, dest)
		if err != nil {
			return nil, err
		}
		return buff.Bytes(), nil

	default:
		return nil, ErrInvalidOption

	}

}