package tga import (	"encoding/binary"	"errors"	"image"	"image/draw"	"io") // Encode encodes an image into TARGA format.func Encode(w io.Writer, m image.Image) (err error) {	b := m.Bounds()	mw, mh := b.Dx(), b.Dy() 	h := rawHeader{		Width:  uint16(mw),		Height: uint16(mh),	} 	if int(h.Width) != mw || int(h.Height) != mh {		return errors.New("uint16 width/height overflow")	} 	h.Flags = flagOriginTop 	switch tm := m.(type) {	case *image.Gray:		h.ImageType = imageTypeMonoChrome		err = encodeGray(w, tm, h) 	case *image.NRGBA:		h.ImageType = imageTypeTrueColor		err = encodeRGBA(w, tm, h, attrTypeAlpha) 	case *image.RGBA:		h.ImageType = imageTypeTrueColor		err = encodeRGBA(w, (*image.NRGBA)(tm), h, attrTypePremultipliedAlpha) 	default:		// convert to non-premultiplied alpha by default		h.ImageType = imageTypeTrueColor		newm := image.NewNRGBA(b)		draw.Draw(newm, b, m, b.Min, draw.Src)		err = encodeRGBA(w, newm, h, attrTypeAlpha)	} 	return} func encodeGray(w io.Writer, m *image.Gray, h rawHeader) (err error) {	h.BPP = 8 // 8-bit monochrome 	if err = binary.Write(w, binary.LittleEndian, &h); err != nil {		return	} 	offset := -(m.Rect.Min.Y*m.Stride + m.Rect.Min.X)	max := offset + int(h.Height)*m.Stride 	for ; offset < max; offset += m.Stride {		if _, err = w.Write(m.Pix[offset : offset+int(h.Width)]); err != nil {			return		}	} 	// no extension area, only a footer	err = binary.Write(w, binary.LittleEndian, newFooter()) 	return} func encodeRGBA(w io.Writer, m *image.NRGBA, h rawHeader, attrType byte) (err error) {	h.BPP = 32   // always save as 32-bit (faster this way)	h.Flags |= 8 // 8-bit alpha channel 	if err = binary.Write(w, binary.LittleEndian, &h); err != nil {		return	} 	lineSize := int(h.Width) * 4	offset := -m.Rect.Min.Y*m.Stride - m.Rect.Min.X*4	max := offset + int(h.Height)*m.Stride	b := make([]byte, lineSize) 	for ; offset < max; offset += m.Stride {		copy(b, m.Pix[offset:offset+lineSize]) 		for i := 0; i < lineSize; i += 4 {			b[i+0], b[i+2] = b[i+2], b[i+0] // RGBA -> BGRA		} 		if _, err = w.Write(b); err != nil {			return		}	} 	// add extension area and footer to define attribute type	_, err = w.Write(newExtArea(attrType))	footer := newFooter()	footer.ExtAreaOffset = uint32(tgaRawHeaderSize + int(h.Height)*lineSize)	err = binary.Write(w, binary.LittleEndian, footer) 	return}