76 lines
1.8 KiB
Go
76 lines
1.8 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package webp implements a decoder for WEBP images.
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//
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// WEBP is defined in the VP8 specification at:
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// http://datatracker.ietf.org/doc/rfc6386/
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package webp
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import (
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"errors"
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"image"
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"image/color"
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"io"
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"code.google.com/p/go.image/vp8"
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)
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func decode(r io.Reader) (d *vp8.Decoder, fh vp8.FrameHeader, err error) {
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var b [20]byte
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if _, err = io.ReadFull(r, b[:]); err != nil {
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return
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}
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if string(b[0:4]) != "RIFF" || string(b[8:16]) != "WEBPVP8 " {
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err = errors.New("webp: invalid format")
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return
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}
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riffLen := uint32(b[4]) | uint32(b[5])<<8 | uint32(b[6])<<16 | uint32(b[7])<<24
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dataLen := uint32(b[16]) | uint32(b[17])<<8 | uint32(b[18])<<16 | uint32(b[19])<<24
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if riffLen < dataLen+12 {
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err = errors.New("webp: invalid format")
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return
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}
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if dataLen >= 1<<31 {
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err = errors.New("webp: invalid format")
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return
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}
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d = vp8.NewDecoder()
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d.Init(r, int(dataLen))
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fh, err = d.DecodeFrameHeader()
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if err != nil {
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d, fh = nil, vp8.FrameHeader{}
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return
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}
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return
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}
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// Decode reads a WEBP image from r and returns it as an image.Image.
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func Decode(r io.Reader) (image.Image, error) {
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d, _, err := decode(r)
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if err != nil {
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return nil, err
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}
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return d.DecodeFrame()
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}
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// DecodeConfig returns the color model and dimensions of a WEBP image without
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// decoding the entire image.
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func DecodeConfig(r io.Reader) (image.Config, error) {
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_, fh, err := decode(r)
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if err != nil {
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return image.Config{}, err
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}
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c := image.Config{
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ColorModel: color.YCbCrModel,
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Width: fh.Width,
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Height: fh.Height,
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}
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return c, nil
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}
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func init() {
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image.RegisterFormat("webp", "RIFF????WEBPVP8 ", Decode, DecodeConfig)
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}
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