| // 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 webp implements a decoder for WEBP images. |
| // |
| // WEBP is defined in the VP8 specification at: |
| // http://datatracker.ietf.org/doc/rfc6386/ |
| package webp |
| |
| import ( |
| "errors" |
| "image" |
| "image/color" |
| "io" |
| |
| "code.google.com/p/go.image/vp8" |
| ) |
| |
| func decode(r io.Reader) (d *vp8.Decoder, fh vp8.FrameHeader, err error) { |
| var b [20]byte |
| if _, err = io.ReadFull(r, b[:]); err != nil { |
| return |
| } |
| if string(b[0:4]) != "RIFF" || string(b[8:16]) != "WEBPVP8 " { |
| err = errors.New("webp: invalid format") |
| return |
| } |
| riffLen := uint32(b[4]) | uint32(b[5])<<8 | uint32(b[6])<<16 | uint32(b[7])<<24 |
| dataLen := uint32(b[16]) | uint32(b[17])<<8 | uint32(b[18])<<16 | uint32(b[19])<<24 |
| if riffLen < dataLen+12 { |
| err = errors.New("webp: invalid format") |
| return |
| } |
| if dataLen >= 1<<31 { |
| err = errors.New("webp: invalid format") |
| return |
| } |
| d = vp8.NewDecoder() |
| d.Init(r, int(dataLen)) |
| fh, err = d.DecodeFrameHeader() |
| if err != nil { |
| d, fh = nil, vp8.FrameHeader{} |
| return |
| } |
| return |
| } |
| |
| // Decode reads a WEBP image from r and returns it as an image.Image. |
| func Decode(r io.Reader) (image.Image, error) { |
| d, _, err := decode(r) |
| if err != nil { |
| return nil, err |
| } |
| return d.DecodeFrame() |
| } |
| |
| // DecodeConfig returns the color model and dimensions of a WEBP image without |
| // decoding the entire image. |
| func DecodeConfig(r io.Reader) (image.Config, error) { |
| _, fh, err := decode(r) |
| if err != nil { |
| return image.Config{}, err |
| } |
| c := image.Config{ |
| ColorModel: color.YCbCrModel, |
| Width: fh.Width, |
| Height: fh.Height, |
| } |
| return c, nil |
| } |
| |
| func init() { |
| image.RegisterFormat("webp", "RIFF????WEBPVP8 ", Decode, DecodeConfig) |
| } |