--- /dev/null
+// Copyright 2011 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 implements a BMP image decoder.
+//
+// The BMP specification is at http://www.digicamsoft.com/bmp/bmp.html.
+package bmp
+
+import (
+ "image"
+ "io"
+ "os"
+)
+
+// ErrUnsupported means that the input BMP image uses a valid but unsupported
+// feature.
+var ErrUnsupported = os.NewError("bmp: unsupported BMP image")
+
+func readUint16(b []byte) uint16 {
+ return uint16(b[0]) | uint16(b[1])<<8
+}
+
+func readUint32(b []byte) uint32 {
+ return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+}
+
+// decodePaletted reads an 8 bit-per-pixel BMP image from r.
+func decodePaletted(r io.Reader, c image.Config) (image.Image, os.Error) {
+ var tmp [4]byte
+ paletted := image.NewPaletted(c.Width, c.Height, c.ColorModel.(image.PalettedColorModel))
+ // BMP images are stored bottom-up rather than top-down.
+ for y := c.Height - 1; y >= 0; y-- {
+ p := paletted.Pix[y*paletted.Stride : y*paletted.Stride+c.Width]
+ _, err := io.ReadFull(r, p)
+ if err != nil {
+ return nil, err
+ }
+ // Each row is 4-byte aligned.
+ if c.Width%4 != 0 {
+ _, err := io.ReadFull(r, tmp[:4-c.Width%4])
+ if err != nil {
+ return nil, err
+ }
+ }
+ }
+ return paletted, nil
+}
+
+// decodeRGBA reads a 24 bit-per-pixel BMP image from r.
+func decodeRGBA(r io.Reader, c image.Config) (image.Image, os.Error) {
+ rgba := image.NewRGBA(c.Width, c.Height)
+ // There are 3 bytes per pixel, and each row is 4-byte aligned.
+ b := make([]byte, (3*c.Width+3)&^3)
+ // BMP images are stored bottom-up rather than top-down.
+ for y := c.Height - 1; y >= 0; y-- {
+ _, err := io.ReadFull(r, b)
+ if err != nil {
+ return nil, err
+ }
+ p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width]
+ for x := range p {
+ // BMP images are stored in BGR order rather than RGB order.
+ p[x] = image.RGBAColor{b[3*x+2], b[3*x+1], b[3*x+0], 0xFF}
+ }
+ }
+ return rgba, nil
+}
+
+// Decode reads a BMP image from r and returns it as an image.Image.
+// Limitation: The file must be 8 or 24 bits per pixel.
+func Decode(r io.Reader) (image.Image, os.Error) {
+ c, err := DecodeConfig(r)
+ if err != nil {
+ return nil, err
+ }
+ if c.ColorModel == image.RGBAColorModel {
+ return decodeRGBA(r, c)
+ }
+ return decodePaletted(r, c)
+}
+
+// DecodeConfig returns the color model and dimensions of a BMP image without
+// decoding the entire image.
+// Limitation: The file must be 8 or 24 bits per pixel.
+func DecodeConfig(r io.Reader) (config image.Config, err os.Error) {
+ // We only support those BMP images that are a BITMAPFILEHEADER
+ // immediately followed by a BITMAPINFOHEADER.
+ const (
+ fileHeaderLen = 14
+ infoHeaderLen = 40
+ )
+ var b [1024]byte
+ if _, err = io.ReadFull(r, b[:fileHeaderLen+infoHeaderLen]); err != nil {
+ return
+ }
+ if string(b[:2]) != "BM" {
+ err = os.NewError("bmp: invalid format")
+ return
+ }
+ offset := readUint32(b[10:14])
+ if readUint32(b[14:18]) != infoHeaderLen {
+ err = ErrUnsupported
+ return
+ }
+ width := int(readUint32(b[18:22]))
+ height := int(readUint32(b[22:26]))
+ if width < 0 || height < 0 {
+ err = ErrUnsupported
+ return
+ }
+ // We only support 1 plane, 8 or 24 bits per pixel and no compression.
+ planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34])
+ if planes != 1 || compression != 0 {
+ err = ErrUnsupported
+ return
+ }
+ switch bpp {
+ case 8:
+ if offset != fileHeaderLen+infoHeaderLen+256*4 {
+ err = ErrUnsupported
+ return
+ }
+ _, err = io.ReadFull(r, b[:256*4])
+ if err != nil {
+ return
+ }
+ pcm := make(image.PalettedColorModel, 256)
+ for i := range pcm {
+ // BMP images are stored in BGR order rather than RGB order.
+ // Every 4th byte is padding.
+ pcm[i] = image.RGBAColor{b[4*i+2], b[4*i+1], b[4*i+0], 0xFF}
+ }
+ return image.Config{pcm, width, height}, nil
+ case 24:
+ if offset != fileHeaderLen+infoHeaderLen {
+ err = ErrUnsupported
+ return
+ }
+ return image.Config{image.RGBAColorModel, width, height}, nil
+ }
+ err = ErrUnsupported
+ return
+}
+
+func init() {
+ image.RegisterFormat("bmp", "BM????\x00\x00\x00\x00", Decode, DecodeConfig)
+}