util.go

package go_qoi

import (
	"bufio"
	"encoding/binary"
	"image"
	"image/color"
	"image/png"
	"io"
	"os"
)

const (
	QOI_OP_INDEX         = 0x00
	QOI_OP_DIFF          = 0x40
	QOI_OP_LUMA          = 0x80
	QOI_OP_RUN           = 0xC0
	QOI_OP_RGB           = 0xFE
	QOI_OP_RGBA          = 0xFF
	QOI_OP_MASK2         = 0xC0
	QOI_MAGIC            = "qoif"
	QOI_END_PADDING_SIZE = 8
	QOI_HEADER_SIZE      = 14
)

var QOI_END_PADDING = [8]byte{0, 0, 0, 0, 0, 0, 0, 1}

func readUint32(reader *bufio.Reader) (uint32, error) {
	bytes := make([]byte, 4)
	_, err := reader.Read(bytes)
	if err != nil {
		return 0, err
	}
	value := binary.BigEndian.Uint32(bytes)
	return value, nil
}

func writeUint32(writer io.Writer, value uint32) error {
	bytes := make([]byte, 4)
	binary.BigEndian.PutUint32(bytes, value)
	_, err := writer.Write(bytes)
	if err != nil {
		return err
	}
	return nil
}

func colorToNRGBA(c color.Color) color.NRGBA {
	return color.NRGBAModel.Convert(c).(color.NRGBA)
}

func colorEquals(c, o color.Color) bool {
	c1 := colorToNRGBA(c)
	o1 := colorToNRGBA(o)
	return c1 == o1
}

func indexPositionHash(px color.NRGBA) uint8 {
	return (px.R*3 + px.G*5 + px.B*7 + px.A*11) % 64
}

// Calculate the maximum (worst case) number of bytes necessary to convert the image.
func MaxQoiSize(img image.Image) int {
	channels := 4
	b := img.Bounds().Max
	return b.X*b.Y*(channels+1) +
		QOI_HEADER_SIZE +
		QOI_END_PADDING_SIZE
}

func ReadPngFile(filename string) (image.Image, error) {
	i, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer i.Close()

	img, err := png.Decode(i)
	if err != nil {
		return nil, err
	}

	return img, nil
}

func ReadQoiFile(filename string) (image.Image, error) {
	i, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer i.Close()

	img, err := Decode(i)
	if err != nil {
		return nil, err
	}

	return img, nil
}

func SaveImageToPngFile(img *image.Image, filename string) error {
	f, err := os.Create(filename)
	if err != nil {
		return err
	}

	if err := png.Encode(f, *img); err != nil {
		f.Close()
		return err
	}

	if err := f.Close(); err != nil {
		return err
	}

	return nil
}

func ReadPngAndSaveImageToQoi(input, output string) error {
	o, err := os.Create(output)
	if err != nil {
		return err
	}
	defer o.Close()

	img, err := ReadPngFile(input)

	if err := Encode(o, img); err != nil {
		return err
	}

	return nil
}