helpers.go

package imaging

import (
	"bytes"
	"errors"
	"image"
	"image/color"
	"image/draw"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"os"
	"path/filepath"
	"strings"

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

// Format is an image file format.
type Format int

// Image file formats.
const (
	JPEG Format = iota
	PNG
	GIF
	TIFF
	BMP
)

func (f Format) String() string {
	switch f {
	case JPEG:
		return "JPEG"
	case PNG:
		return "PNG"
	case GIF:
		return "GIF"
	case TIFF:
		return "TIFF"
	case BMP:
		return "BMP"
	default:
		return "Unsupported"
	}
}

var formatFromExt = map[string]Format{
	".jpg":  JPEG,
	".jpeg": JPEG,
	".png":  PNG,
	".tif":  TIFF,
	".tiff": TIFF,
	".bmp":  BMP,
	".gif":  GIF,
}

// FormatFromFilename parses image format from filename extension:
// "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.
func FormatFromFilename(filename string) (Format, error) {
	ext := strings.ToLower(filepath.Ext(filename))
	if f, ok := formatFromExt[ext]; ok {
		return f, nil
	}
	return -1, ErrUnsupportedFormat
}

var (
	// ErrUnsupportedFormat means the given image format (or file extension) is unsupported.
	ErrUnsupportedFormat = errors.New("imaging: unsupported image format")
)

type fileSystem interface {
	Create(string) (io.WriteCloser, error)
	Open(string) (io.ReadCloser, error)
}

type localFS struct{}

func (localFS) Create(name string) (io.WriteCloser, error) { return os.Create(name) }
func (localFS) Open(name string) (io.ReadCloser, error)    { return os.Open(name) }

var fs fileSystem = localFS{}

// Decode reads an image from r.
func Decode(r io.Reader) (image.Image, error) {
	img, _, err := image.Decode(r)
	return img, err
}

// Open loads an image from file
func Open(filename string) (image.Image, error) {
	file, err := fs.Open(filename)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	return Decode(file)
}

type encodeConfig struct {
	jpegQuality         int
	gifNumColors        int
	gifQuantizer        draw.Quantizer
	gifDrawer           draw.Drawer
	pngCompressionLevel png.CompressionLevel
}

var defaultEncodeConfig = encodeConfig{
	jpegQuality:         95,
	gifNumColors:        256,
	gifQuantizer:        nil,
	gifDrawer:           nil,
	pngCompressionLevel: png.DefaultCompression,
}

// EncodeOption sets an optional parameter for the Encode and Save functions.
type EncodeOption func(*encodeConfig)

// JPEGQuality returns an EncodeOption that sets the output JPEG quality.
// Quality ranges from 1 to 100 inclusive, higher is better. Default is 95.
func JPEGQuality(quality int) EncodeOption {
	return func(c *encodeConfig) {
		c.jpegQuality = quality
	}
}

// GIFNumColors returns an EncodeOption that sets the maximum number of colors
// used in the GIF-encoded image. It ranges from 1 to 256.  Default is 256.
func GIFNumColors(numColors int) EncodeOption {
	return func(c *encodeConfig) {
		c.gifNumColors = numColors
	}
}

// GIFQuantizer returns an EncodeOption that sets the quantizer that is used to produce
// a palette of the GIF-encoded image.
func GIFQuantizer(quantizer draw.Quantizer) EncodeOption {
	return func(c *encodeConfig) {
		c.gifQuantizer = quantizer
	}
}

// GIFDrawer returns an EncodeOption that sets the drawer that is used to convert
// the source image to the desired palette of the GIF-encoded image.
func GIFDrawer(drawer draw.Drawer) EncodeOption {
	return func(c *encodeConfig) {
		c.gifDrawer = drawer
	}
}

// PNGCompressionLevel returns an EncodeOption that sets the compression level
// of the PNG-encoded image. Default is png.DefaultCompression.
func PNGCompressionLevel(level png.CompressionLevel) EncodeOption {
	return func(c *encodeConfig) {
		c.pngCompressionLevel = level
	}
}

// Encode writes the image img to w in the specified format (JPEG, PNG, GIF, TIFF or BMP).
func Encode(w io.Writer, img image.Image, format Format, opts ...EncodeOption) error {
	cfg := defaultEncodeConfig
	for _, option := range opts {
		option(&cfg)
	}

	var err error
	switch format {
	case JPEG:
		var rgba *image.RGBA
		if nrgba, ok := img.(*image.NRGBA); ok {
			if nrgba.Opaque() {
				rgba = &image.RGBA{
					Pix:    nrgba.Pix,
					Stride: nrgba.Stride,
					Rect:   nrgba.Rect,
				}
			}
		}
		if rgba != nil {
			err = jpeg.Encode(w, rgba, &jpeg.Options{Quality: cfg.jpegQuality})
		} else {
			err = jpeg.Encode(w, img, &jpeg.Options{Quality: cfg.jpegQuality})
		}

	case PNG:
		enc := png.Encoder{CompressionLevel: cfg.pngCompressionLevel}
		err = enc.Encode(w, img)

	case GIF:
		err = gif.Encode(w, img, &gif.Options{
			NumColors: cfg.gifNumColors,
			Quantizer: cfg.gifQuantizer,
			Drawer:    cfg.gifDrawer,
		})

	case TIFF:
		err = tiff.Encode(w, img, &tiff.Options{Compression: tiff.Deflate, Predictor: true})

	case BMP:
		err = bmp.Encode(w, img)

	default:
		err = ErrUnsupportedFormat
	}
	return err
}

// Save saves the image to file with the specified filename.
// The format is determined from the filename extension: "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.
//
// Examples:
//
//	// Save the image as PNG.
//	err := imaging.Save(img, "out.png")
//
//	// Save the image as JPEG with optional quality parameter set to 80.
//	err := imaging.Save(img, "out.jpg", imaging.JPEGQuality(80))
//
func Save(img image.Image, filename string, opts ...EncodeOption) (err error) {
	f, err := FormatFromFilename(filename)
	if err != nil {
		return err
	}
	file, err := fs.Create(filename)
	if err != nil {
		return err
	}

	defer func() {
		cerr := file.Close()
		if err == nil {
			err = cerr
		}
	}()

	return Encode(file, img, f, opts...)
}

// New creates a new image with the specified width and height, and fills it with the specified color.
func New(width, height int, fillColor color.Color) *image.NRGBA {
	if width <= 0 || height <= 0 {
		return &image.NRGBA{}
	}

	c := color.NRGBAModel.Convert(fillColor).(color.NRGBA)
	if (c == color.NRGBA{0, 0, 0, 0}) {
		return image.NewNRGBA(image.Rect(0, 0, width, height))
	}

	return &image.NRGBA{
		Pix:    bytes.Repeat([]byte{c.R, c.G, c.B, c.A}, width*height),
		Stride: 4 * width,
		Rect:   image.Rect(0, 0, width, height),
	}
}

// Clone returns a copy of the given image.
func Clone(img image.Image) *image.NRGBA {
	src := newScanner(img)
	dst := image.NewNRGBA(image.Rect(0, 0, src.w, src.h))
	size := src.w * 4
	parallel(0, src.h, func(ys <-chan int) {
		for y := range ys {
			i := y * dst.Stride
			src.scan(0, y, src.w, y+1, dst.Pix[i:i+size])
		}
	})
	return dst
}