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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bmp
import (
"encoding/binary"
"errors"
"image"
"io"
)
type header struct {
sigBM [2]byte
fileSize uint32
resverved [2]uint16
pixOffset uint32
dibHeaderSize uint32
width uint32
height uint32
colorPlane uint16
bpp uint16
compression uint32
imageSize uint32
xPixelsPerMeter uint32
yPixelsPerMeter uint32
colorUse uint32
colorImportant uint32
}
func encodePaletted(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
var padding []byte
if dx < step {
padding = make([]byte, step-dx)
}
for y := dy - 1; y >= 0; y-- {
min := y*stride + 0
max := y*stride + dx
if _, err := w.Write(pix[min:max]); err != nil {
return err
}
if padding != nil {
if _, err := w.Write(padding); err != nil {
return err
}
}
}
return nil
}
func encodeRGBA(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
buf := make([]byte, step)
for y := dy - 1; y >= 0; y-- {
min := y*stride + 0
max := y*stride + dx*4
off := 0
for i := min; i < max; i += 4 {
buf[off+2] = pix[i+0]
buf[off+1] = pix[i+1]
buf[off+0] = pix[i+2]
off += 3
}
if _, err := w.Write(buf); err != nil {
return err
}
}
return nil
}
func encode(w io.Writer, m image.Image, step int) error {
b := m.Bounds()
buf := make([]byte, step)
for y := b.Max.Y - 1; y >= b.Min.Y; y-- {
off := 0
for x := b.Min.X; x < b.Max.X; x++ {
r, g, b, _ := m.At(x, y).RGBA()
buf[off+2] = byte(r >> 8)
buf[off+1] = byte(g >> 8)
buf[off+0] = byte(b >> 8)
off += 3
}
if _, err := w.Write(buf); err != nil {
return err
}
}
return nil
}
// Encode writes the image m to w in BMP format.
func Encode(w io.Writer, m image.Image) error {
d := m.Bounds().Size()
if d.X < 0 || d.Y < 0 {
return errors.New("bmp: negative bounds")
}
h := &header{
sigBM: [2]byte{'B', 'M'},
fileSize: 14 + 40,
pixOffset: 14 + 40,
dibHeaderSize: 40,
width: uint32(d.X),
height: uint32(d.Y),
colorPlane: 1,
}
var step int
var palette []byte
switch m := m.(type) {
case *image.Gray:
step = (d.X + 3) &^ 3
palette = make([]byte, 1024)
for i := 0; i < 256; i++ {
palette[i*4+0] = uint8(i)
palette[i*4+1] = uint8(i)
palette[i*4+2] = uint8(i)
palette[i*4+3] = 0xFF
}
h.imageSize = uint32(d.Y * step)
h.fileSize += uint32(len(palette)) + h.imageSize
h.pixOffset += uint32(len(palette))
h.bpp = 8
case *image.Paletted:
step = (d.X + 3) &^ 3
palette = make([]byte, 1024)
for i := 0; i < len(m.Palette) && i < 256; i++ {
r, g, b, _ := m.Palette[i].RGBA()
palette[i*4+0] = uint8(b >> 8)
palette[i*4+1] = uint8(g >> 8)
palette[i*4+2] = uint8(r >> 8)
palette[i*4+3] = 0xFF
}
h.imageSize = uint32(d.Y * step)
h.fileSize += uint32(len(palette)) + h.imageSize
h.pixOffset += uint32(len(palette))
h.bpp = 8
default:
step = (3*d.X + 3) &^ 3
h.imageSize = uint32(d.Y * step)
h.fileSize += h.imageSize
h.bpp = 24
}
if err := binary.Write(w, binary.LittleEndian, h); err != nil {
return err
}
if palette != nil {
if err := binary.Write(w, binary.LittleEndian, palette); err != nil {
return err
}
}
if d.X == 0 || d.Y == 0 {
return nil
}
switch m := m.(type) {
case *image.Gray:
return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
case *image.Paletted:
return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
case *image.RGBA:
return encodeRGBA(w, m.Pix, d.X, d.Y, m.Stride, step)
}
return encode(w, m, step)
}
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