forked from mirrors/gotosocial
1a3f26fb5c
* media: add webp support Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se> * bump exif-terminator to v0.5.0 Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se> Signed-off-by: Sigrid Solveig Haflínudóttir <sigrid@ftrv.se>
603 lines
15 KiB
Go
603 lines
15 KiB
Go
// Copyright 2014 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 vp8l implements a decoder for the VP8L lossless image format.
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//
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// The VP8L specification is at:
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// https://developers.google.com/speed/webp/docs/riff_container
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package vp8l // import "golang.org/x/image/vp8l"
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import (
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"bufio"
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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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)
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var (
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errInvalidCodeLengths = errors.New("vp8l: invalid code lengths")
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errInvalidHuffmanTree = errors.New("vp8l: invalid Huffman tree")
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)
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// colorCacheMultiplier is the multiplier used for the color cache hash
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// function, specified in section 4.2.3.
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const colorCacheMultiplier = 0x1e35a7bd
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// distanceMapTable is the look-up table for distanceMap.
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var distanceMapTable = [120]uint8{
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0x18, 0x07, 0x17, 0x19, 0x28, 0x06, 0x27, 0x29, 0x16, 0x1a,
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0x26, 0x2a, 0x38, 0x05, 0x37, 0x39, 0x15, 0x1b, 0x36, 0x3a,
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0x25, 0x2b, 0x48, 0x04, 0x47, 0x49, 0x14, 0x1c, 0x35, 0x3b,
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0x46, 0x4a, 0x24, 0x2c, 0x58, 0x45, 0x4b, 0x34, 0x3c, 0x03,
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0x57, 0x59, 0x13, 0x1d, 0x56, 0x5a, 0x23, 0x2d, 0x44, 0x4c,
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0x55, 0x5b, 0x33, 0x3d, 0x68, 0x02, 0x67, 0x69, 0x12, 0x1e,
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0x66, 0x6a, 0x22, 0x2e, 0x54, 0x5c, 0x43, 0x4d, 0x65, 0x6b,
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0x32, 0x3e, 0x78, 0x01, 0x77, 0x79, 0x53, 0x5d, 0x11, 0x1f,
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0x64, 0x6c, 0x42, 0x4e, 0x76, 0x7a, 0x21, 0x2f, 0x75, 0x7b,
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0x31, 0x3f, 0x63, 0x6d, 0x52, 0x5e, 0x00, 0x74, 0x7c, 0x41,
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0x4f, 0x10, 0x20, 0x62, 0x6e, 0x30, 0x73, 0x7d, 0x51, 0x5f,
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0x40, 0x72, 0x7e, 0x61, 0x6f, 0x50, 0x71, 0x7f, 0x60, 0x70,
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}
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// distanceMap maps a LZ77 backwards reference distance to a two-dimensional
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// pixel offset, specified in section 4.2.2.
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func distanceMap(w int32, code uint32) int32 {
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if int32(code) > int32(len(distanceMapTable)) {
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return int32(code) - int32(len(distanceMapTable))
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}
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distCode := int32(distanceMapTable[code-1])
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yOffset := distCode >> 4
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xOffset := 8 - distCode&0xf
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if d := yOffset*w + xOffset; d >= 1 {
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return d
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}
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return 1
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}
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// decoder holds the bit-stream for a VP8L image.
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type decoder struct {
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r io.ByteReader
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bits uint32
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nBits uint32
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}
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// read reads the next n bits from the decoder's bit-stream.
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func (d *decoder) read(n uint32) (uint32, error) {
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for d.nBits < n {
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c, err := d.r.ReadByte()
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if err != nil {
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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return 0, err
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}
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d.bits |= uint32(c) << d.nBits
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d.nBits += 8
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}
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u := d.bits & (1<<n - 1)
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d.bits >>= n
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d.nBits -= n
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return u, nil
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}
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// decodeTransform decodes the next transform and the width of the image after
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// transformation (or equivalently, before inverse transformation), specified
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// in section 3.
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func (d *decoder) decodeTransform(w int32, h int32) (t transform, newWidth int32, err error) {
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t.oldWidth = w
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t.transformType, err = d.read(2)
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if err != nil {
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return transform{}, 0, err
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}
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switch t.transformType {
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case transformTypePredictor, transformTypeCrossColor:
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t.bits, err = d.read(3)
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if err != nil {
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return transform{}, 0, err
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}
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t.bits += 2
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t.pix, err = d.decodePix(nTiles(w, t.bits), nTiles(h, t.bits), 0, false)
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if err != nil {
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return transform{}, 0, err
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}
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case transformTypeSubtractGreen:
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// No-op.
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case transformTypeColorIndexing:
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nColors, err := d.read(8)
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if err != nil {
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return transform{}, 0, err
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}
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nColors++
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t.bits = 0
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switch {
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case nColors <= 2:
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t.bits = 3
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case nColors <= 4:
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t.bits = 2
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case nColors <= 16:
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t.bits = 1
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}
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w = nTiles(w, t.bits)
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pix, err := d.decodePix(int32(nColors), 1, 4*256, false)
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if err != nil {
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return transform{}, 0, err
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}
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for p := 4; p < len(pix); p += 4 {
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pix[p+0] += pix[p-4]
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pix[p+1] += pix[p-3]
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pix[p+2] += pix[p-2]
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pix[p+3] += pix[p-1]
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}
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// The spec says that "if the index is equal or larger than color_table_size,
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// the argb color value should be set to 0x00000000 (transparent black)."
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// We re-slice up to 256 4-byte pixels.
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t.pix = pix[:4*256]
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}
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return t, w, nil
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}
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// repeatsCodeLength is the minimum code length for repeated codes.
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const repeatsCodeLength = 16
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// These magic numbers are specified at the end of section 5.2.2.
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// The 3-length arrays apply to code lengths >= repeatsCodeLength.
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var (
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codeLengthCodeOrder = [19]uint8{
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17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
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}
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repeatBits = [3]uint8{2, 3, 7}
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repeatOffsets = [3]uint8{3, 3, 11}
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)
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// decodeCodeLengths decodes a Huffman tree's code lengths which are themselves
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// encoded via a Huffman tree, specified in section 5.2.2.
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func (d *decoder) decodeCodeLengths(dst []uint32, codeLengthCodeLengths []uint32) error {
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h := hTree{}
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if err := h.build(codeLengthCodeLengths); err != nil {
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return err
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}
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maxSymbol := len(dst)
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useLength, err := d.read(1)
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if err != nil {
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return err
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}
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if useLength != 0 {
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n, err := d.read(3)
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if err != nil {
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return err
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}
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n = 2 + 2*n
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ms, err := d.read(n)
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if err != nil {
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return err
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}
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maxSymbol = int(ms) + 2
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if maxSymbol > len(dst) {
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return errInvalidCodeLengths
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}
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}
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// The spec says that "if code 16 [meaning repeat] is used before
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// a non-zero value has been emitted, a value of 8 is repeated."
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prevCodeLength := uint32(8)
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for symbol := 0; symbol < len(dst); {
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if maxSymbol == 0 {
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break
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}
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maxSymbol--
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codeLength, err := h.next(d)
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if err != nil {
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return err
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}
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if codeLength < repeatsCodeLength {
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dst[symbol] = codeLength
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symbol++
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if codeLength != 0 {
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prevCodeLength = codeLength
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}
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continue
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}
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repeat, err := d.read(uint32(repeatBits[codeLength-repeatsCodeLength]))
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if err != nil {
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return err
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}
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repeat += uint32(repeatOffsets[codeLength-repeatsCodeLength])
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if symbol+int(repeat) > len(dst) {
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return errInvalidCodeLengths
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}
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// A code length of 16 repeats the previous non-zero code.
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// A code length of 17 or 18 repeats zeroes.
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cl := uint32(0)
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if codeLength == 16 {
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cl = prevCodeLength
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}
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for ; repeat > 0; repeat-- {
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dst[symbol] = cl
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symbol++
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}
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}
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return nil
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}
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// decodeHuffmanTree decodes a Huffman tree into h.
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func (d *decoder) decodeHuffmanTree(h *hTree, alphabetSize uint32) error {
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useSimple, err := d.read(1)
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if err != nil {
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return err
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}
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if useSimple != 0 {
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nSymbols, err := d.read(1)
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if err != nil {
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return err
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}
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nSymbols++
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firstSymbolLengthCode, err := d.read(1)
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if err != nil {
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return err
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}
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firstSymbolLengthCode = 7*firstSymbolLengthCode + 1
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var symbols [2]uint32
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symbols[0], err = d.read(firstSymbolLengthCode)
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if err != nil {
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return err
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}
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if nSymbols == 2 {
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symbols[1], err = d.read(8)
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if err != nil {
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return err
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}
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}
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return h.buildSimple(nSymbols, symbols, alphabetSize)
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}
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nCodes, err := d.read(4)
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if err != nil {
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return err
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}
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nCodes += 4
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if int(nCodes) > len(codeLengthCodeOrder) {
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return errInvalidHuffmanTree
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}
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codeLengthCodeLengths := [len(codeLengthCodeOrder)]uint32{}
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for i := uint32(0); i < nCodes; i++ {
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codeLengthCodeLengths[codeLengthCodeOrder[i]], err = d.read(3)
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if err != nil {
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return err
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}
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}
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codeLengths := make([]uint32, alphabetSize)
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if err = d.decodeCodeLengths(codeLengths, codeLengthCodeLengths[:]); err != nil {
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return err
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}
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return h.build(codeLengths)
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}
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const (
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huffGreen = 0
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huffRed = 1
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huffBlue = 2
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huffAlpha = 3
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huffDistance = 4
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nHuff = 5
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)
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// hGroup is an array of 5 Huffman trees.
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type hGroup [nHuff]hTree
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// decodeHuffmanGroups decodes the one or more hGroups used to decode the pixel
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// data. If one hGroup is used for the entire image, then hPix and hBits will
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// be zero. If more than one hGroup is used, then hPix contains the meta-image
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// that maps tiles to hGroup index, and hBits contains the log-2 tile size.
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func (d *decoder) decodeHuffmanGroups(w int32, h int32, topLevel bool, ccBits uint32) (
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hGroups []hGroup, hPix []byte, hBits uint32, err error) {
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maxHGroupIndex := 0
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if topLevel {
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useMeta, err := d.read(1)
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if err != nil {
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return nil, nil, 0, err
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}
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if useMeta != 0 {
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hBits, err = d.read(3)
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if err != nil {
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return nil, nil, 0, err
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}
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hBits += 2
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hPix, err = d.decodePix(nTiles(w, hBits), nTiles(h, hBits), 0, false)
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if err != nil {
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return nil, nil, 0, err
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}
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for p := 0; p < len(hPix); p += 4 {
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i := int(hPix[p])<<8 | int(hPix[p+1])
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if maxHGroupIndex < i {
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maxHGroupIndex = i
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}
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}
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}
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}
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hGroups = make([]hGroup, maxHGroupIndex+1)
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for i := range hGroups {
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for j, alphabetSize := range alphabetSizes {
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if j == 0 && ccBits > 0 {
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alphabetSize += 1 << ccBits
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}
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if err := d.decodeHuffmanTree(&hGroups[i][j], alphabetSize); err != nil {
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return nil, nil, 0, err
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}
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}
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}
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return hGroups, hPix, hBits, nil
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}
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const (
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nLiteralCodes = 256
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nLengthCodes = 24
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nDistanceCodes = 40
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)
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var alphabetSizes = [nHuff]uint32{
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nLiteralCodes + nLengthCodes,
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nLiteralCodes,
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nLiteralCodes,
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nLiteralCodes,
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nDistanceCodes,
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}
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// decodePix decodes pixel data, specified in section 5.2.2.
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func (d *decoder) decodePix(w int32, h int32, minCap int32, topLevel bool) ([]byte, error) {
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// Decode the color cache parameters.
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ccBits, ccShift, ccEntries := uint32(0), uint32(0), ([]uint32)(nil)
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useColorCache, err := d.read(1)
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if err != nil {
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return nil, err
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}
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if useColorCache != 0 {
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ccBits, err = d.read(4)
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if err != nil {
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return nil, err
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}
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if ccBits < 1 || 11 < ccBits {
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return nil, errors.New("vp8l: invalid color cache parameters")
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}
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ccShift = 32 - ccBits
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ccEntries = make([]uint32, 1<<ccBits)
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}
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// Decode the Huffman groups.
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hGroups, hPix, hBits, err := d.decodeHuffmanGroups(w, h, topLevel, ccBits)
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if err != nil {
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return nil, err
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}
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hMask, tilesPerRow := int32(0), int32(0)
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if hBits != 0 {
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hMask, tilesPerRow = 1<<hBits-1, nTiles(w, hBits)
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}
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// Decode the pixels.
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if minCap < 4*w*h {
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minCap = 4 * w * h
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}
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pix := make([]byte, 4*w*h, minCap)
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p, cachedP := 0, 0
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x, y := int32(0), int32(0)
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hg, lookupHG := &hGroups[0], hMask != 0
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for p < len(pix) {
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if lookupHG {
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i := 4 * (tilesPerRow*(y>>hBits) + (x >> hBits))
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hg = &hGroups[uint32(hPix[i])<<8|uint32(hPix[i+1])]
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}
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green, err := hg[huffGreen].next(d)
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if err != nil {
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return nil, err
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}
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switch {
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case green < nLiteralCodes:
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// We have a literal pixel.
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red, err := hg[huffRed].next(d)
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if err != nil {
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return nil, err
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}
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blue, err := hg[huffBlue].next(d)
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if err != nil {
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return nil, err
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}
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alpha, err := hg[huffAlpha].next(d)
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if err != nil {
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return nil, err
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}
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pix[p+0] = uint8(red)
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pix[p+1] = uint8(green)
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pix[p+2] = uint8(blue)
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pix[p+3] = uint8(alpha)
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p += 4
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x++
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if x == w {
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x, y = 0, y+1
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}
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lookupHG = hMask != 0 && x&hMask == 0
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case green < nLiteralCodes+nLengthCodes:
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// We have a LZ77 backwards reference.
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length, err := d.lz77Param(green - nLiteralCodes)
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if err != nil {
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return nil, err
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}
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distSym, err := hg[huffDistance].next(d)
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if err != nil {
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return nil, err
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}
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distCode, err := d.lz77Param(distSym)
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if err != nil {
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return nil, err
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}
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dist := distanceMap(w, distCode)
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pEnd := p + 4*int(length)
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q := p - 4*int(dist)
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qEnd := pEnd - 4*int(dist)
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if p < 0 || len(pix) < pEnd || q < 0 || len(pix) < qEnd {
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return nil, errors.New("vp8l: invalid LZ77 parameters")
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}
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for ; p < pEnd; p, q = p+1, q+1 {
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pix[p] = pix[q]
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}
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x += int32(length)
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for x >= w {
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x, y = x-w, y+1
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}
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lookupHG = hMask != 0
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default:
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// We have a color cache lookup. First, insert previous pixels
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// into the cache. Note that VP8L assumes ARGB order, but the
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// Go image.RGBA type is in RGBA order.
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for ; cachedP < p; cachedP += 4 {
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argb := uint32(pix[cachedP+0])<<16 |
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uint32(pix[cachedP+1])<<8 |
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uint32(pix[cachedP+2])<<0 |
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uint32(pix[cachedP+3])<<24
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ccEntries[(argb*colorCacheMultiplier)>>ccShift] = argb
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}
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green -= nLiteralCodes + nLengthCodes
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if int(green) >= len(ccEntries) {
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return nil, errors.New("vp8l: invalid color cache index")
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}
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argb := ccEntries[green]
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pix[p+0] = uint8(argb >> 16)
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pix[p+1] = uint8(argb >> 8)
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pix[p+2] = uint8(argb >> 0)
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pix[p+3] = uint8(argb >> 24)
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p += 4
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x++
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if x == w {
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x, y = 0, y+1
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}
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lookupHG = hMask != 0 && x&hMask == 0
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}
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}
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return pix, nil
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}
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// lz77Param returns the next LZ77 parameter: a length or a distance, specified
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// in section 4.2.2.
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func (d *decoder) lz77Param(symbol uint32) (uint32, error) {
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if symbol < 4 {
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|
return symbol + 1, nil
|
|
}
|
|
extraBits := (symbol - 2) >> 1
|
|
offset := (2 + symbol&1) << extraBits
|
|
n, err := d.read(extraBits)
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
return offset + n + 1, nil
|
|
}
|
|
|
|
// decodeHeader decodes the VP8L header from r.
|
|
func decodeHeader(r io.Reader) (d *decoder, w int32, h int32, err error) {
|
|
rr, ok := r.(io.ByteReader)
|
|
if !ok {
|
|
rr = bufio.NewReader(r)
|
|
}
|
|
d = &decoder{r: rr}
|
|
magic, err := d.read(8)
|
|
if err != nil {
|
|
return nil, 0, 0, err
|
|
}
|
|
if magic != 0x2f {
|
|
return nil, 0, 0, errors.New("vp8l: invalid header")
|
|
}
|
|
width, err := d.read(14)
|
|
if err != nil {
|
|
return nil, 0, 0, err
|
|
}
|
|
width++
|
|
height, err := d.read(14)
|
|
if err != nil {
|
|
return nil, 0, 0, err
|
|
}
|
|
height++
|
|
_, err = d.read(1) // Read and ignore the hasAlpha hint.
|
|
if err != nil {
|
|
return nil, 0, 0, err
|
|
}
|
|
version, err := d.read(3)
|
|
if err != nil {
|
|
return nil, 0, 0, err
|
|
}
|
|
if version != 0 {
|
|
return nil, 0, 0, errors.New("vp8l: invalid version")
|
|
}
|
|
return d, int32(width), int32(height), nil
|
|
}
|
|
|
|
// DecodeConfig decodes the color model and dimensions of a VP8L image from r.
|
|
func DecodeConfig(r io.Reader) (image.Config, error) {
|
|
_, w, h, err := decodeHeader(r)
|
|
if err != nil {
|
|
return image.Config{}, err
|
|
}
|
|
return image.Config{
|
|
ColorModel: color.NRGBAModel,
|
|
Width: int(w),
|
|
Height: int(h),
|
|
}, nil
|
|
}
|
|
|
|
// Decode decodes a VP8L image from r.
|
|
func Decode(r io.Reader) (image.Image, error) {
|
|
d, w, h, err := decodeHeader(r)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
// Decode the transforms.
|
|
var (
|
|
nTransforms int
|
|
transforms [nTransformTypes]transform
|
|
transformsSeen [nTransformTypes]bool
|
|
originalW = w
|
|
)
|
|
for {
|
|
more, err := d.read(1)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
if more == 0 {
|
|
break
|
|
}
|
|
var t transform
|
|
t, w, err = d.decodeTransform(w, h)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
if transformsSeen[t.transformType] {
|
|
return nil, errors.New("vp8l: repeated transform")
|
|
}
|
|
transformsSeen[t.transformType] = true
|
|
transforms[nTransforms] = t
|
|
nTransforms++
|
|
}
|
|
// Decode the transformed pixels.
|
|
pix, err := d.decodePix(w, h, 0, true)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
// Apply the inverse transformations.
|
|
for i := nTransforms - 1; i >= 0; i-- {
|
|
t := &transforms[i]
|
|
pix = inverseTransforms[t.transformType](t, pix, h)
|
|
}
|
|
return &image.NRGBA{
|
|
Pix: pix,
|
|
Stride: 4 * int(originalW),
|
|
Rect: image.Rect(0, 0, int(originalW), int(h)),
|
|
}, nil
|
|
}
|