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Diffstat (limited to 'vendor/golang.org/x/image/vp8/decode.go')
| -rw-r--r-- | vendor/golang.org/x/image/vp8/decode.go | 403 |
1 files changed, 0 insertions, 403 deletions
diff --git a/vendor/golang.org/x/image/vp8/decode.go b/vendor/golang.org/x/image/vp8/decode.go deleted file mode 100644 index 2aa9fee..0000000 --- a/vendor/golang.org/x/image/vp8/decode.go +++ /dev/null @@ -1,403 +0,0 @@ -// 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 vp8 implements a decoder for the VP8 lossy image format. -// -// The VP8 specification is RFC 6386. -package vp8 // import "golang.org/x/image/vp8" - -// This file implements the top-level decoding algorithm. - -import ( - "errors" - "image" - "io" -) - -// limitReader wraps an io.Reader to read at most n bytes from it. -type limitReader struct { - r io.Reader - n int -} - -// ReadFull reads exactly len(p) bytes into p. -func (r *limitReader) ReadFull(p []byte) error { - if len(p) > r.n { - return io.ErrUnexpectedEOF - } - n, err := io.ReadFull(r.r, p) - r.n -= n - return err -} - -// FrameHeader is a frame header, as specified in section 9.1. -type FrameHeader struct { - KeyFrame bool - VersionNumber uint8 - ShowFrame bool - FirstPartitionLen uint32 - Width int - Height int - XScale uint8 - YScale uint8 -} - -const ( - nSegment = 4 - nSegmentProb = 3 -) - -// segmentHeader holds segment-related header information. -type segmentHeader struct { - useSegment bool - updateMap bool - relativeDelta bool - quantizer [nSegment]int8 - filterStrength [nSegment]int8 - prob [nSegmentProb]uint8 -} - -const ( - nRefLFDelta = 4 - nModeLFDelta = 4 -) - -// filterHeader holds filter-related header information. -type filterHeader struct { - simple bool - level int8 - sharpness uint8 - useLFDelta bool - refLFDelta [nRefLFDelta]int8 - modeLFDelta [nModeLFDelta]int8 - perSegmentLevel [nSegment]int8 -} - -// mb is the per-macroblock decode state. A decoder maintains mbw+1 of these -// as it is decoding macroblocks left-to-right and top-to-bottom: mbw for the -// macroblocks in the row above, and one for the macroblock to the left. -type mb struct { - // pred is the predictor mode for the 4 bottom or right 4x4 luma regions. - pred [4]uint8 - // nzMask is a mask of 8 bits: 4 for the bottom or right 4x4 luma regions, - // and 2 + 2 for the bottom or right 4x4 chroma regions. A 1 bit indicates - // that region has non-zero coefficients. - nzMask uint8 - // nzY16 is a 0/1 value that is 1 if the macroblock used Y16 prediction and - // had non-zero coefficients. - nzY16 uint8 -} - -// Decoder decodes VP8 bitstreams into frames. Decoding one frame consists of -// calling Init, DecodeFrameHeader and then DecodeFrame in that order. -// A Decoder can be re-used to decode multiple frames. -type Decoder struct { - // r is the input bitsream. - r limitReader - // scratch is a scratch buffer. - scratch [8]byte - // img is the YCbCr image to decode into. - img *image.YCbCr - // mbw and mbh are the number of 16x16 macroblocks wide and high the image is. - mbw, mbh int - // frameHeader is the frame header. When decoding multiple frames, - // frames that aren't key frames will inherit the Width, Height, - // XScale and YScale of the most recent key frame. - frameHeader FrameHeader - // Other headers. - segmentHeader segmentHeader - filterHeader filterHeader - // The image data is divided into a number of independent partitions. - // There is 1 "first partition" and between 1 and 8 "other partitions" - // for coefficient data. - fp partition - op [8]partition - nOP int - // Quantization factors. - quant [nSegment]quant - // DCT/WHT coefficient decoding probabilities. - tokenProb [nPlane][nBand][nContext][nProb]uint8 - useSkipProb bool - skipProb uint8 - // Loop filter parameters. - filterParams [nSegment][2]filterParam - perMBFilterParams []filterParam - - // The eight fields below relate to the current macroblock being decoded. - // - // Segment-based adjustments. - segment int - // Per-macroblock state for the macroblock immediately left of and those - // macroblocks immediately above the current macroblock. - leftMB mb - upMB []mb - // Bitmasks for which 4x4 regions of coeff contain non-zero coefficients. - nzDCMask, nzACMask uint32 - // Predictor modes. - usePredY16 bool // The libwebp C code calls this !is_i4x4_. - predY16 uint8 - predC8 uint8 - predY4 [4][4]uint8 - - // The two fields below form a workspace for reconstructing a macroblock. - // Their specific sizes are documented in reconstruct.go. - coeff [1*16*16 + 2*8*8 + 1*4*4]int16 - ybr [1 + 16 + 1 + 8][32]uint8 -} - -// NewDecoder returns a new Decoder. -func NewDecoder() *Decoder { - return &Decoder{} -} - -// Init initializes the decoder to read at most n bytes from r. -func (d *Decoder) Init(r io.Reader, n int) { - d.r = limitReader{r, n} -} - -// DecodeFrameHeader decodes the frame header. -func (d *Decoder) DecodeFrameHeader() (fh FrameHeader, err error) { - // All frame headers are at least 3 bytes long. - b := d.scratch[:3] - if err = d.r.ReadFull(b); err != nil { - return - } - d.frameHeader.KeyFrame = (b[0] & 1) == 0 - d.frameHeader.VersionNumber = (b[0] >> 1) & 7 - d.frameHeader.ShowFrame = (b[0]>>4)&1 == 1 - d.frameHeader.FirstPartitionLen = uint32(b[0])>>5 | uint32(b[1])<<3 | uint32(b[2])<<11 - if !d.frameHeader.KeyFrame { - return d.frameHeader, nil - } - // Frame headers for key frames are an additional 7 bytes long. - b = d.scratch[:7] - if err = d.r.ReadFull(b); err != nil { - return - } - // Check the magic sync code. - if b[0] != 0x9d || b[1] != 0x01 || b[2] != 0x2a { - err = errors.New("vp8: invalid format") - return - } - d.frameHeader.Width = int(b[4]&0x3f)<<8 | int(b[3]) - d.frameHeader.Height = int(b[6]&0x3f)<<8 | int(b[5]) - d.frameHeader.XScale = b[4] >> 6 - d.frameHeader.YScale = b[6] >> 6 - d.mbw = (d.frameHeader.Width + 0x0f) >> 4 - d.mbh = (d.frameHeader.Height + 0x0f) >> 4 - d.segmentHeader = segmentHeader{ - prob: [3]uint8{0xff, 0xff, 0xff}, - } - d.tokenProb = defaultTokenProb - d.segment = 0 - return d.frameHeader, nil -} - -// ensureImg ensures that d.img is large enough to hold the decoded frame. -func (d *Decoder) ensureImg() { - if d.img != nil { - p0, p1 := d.img.Rect.Min, d.img.Rect.Max - if p0.X == 0 && p0.Y == 0 && p1.X >= 16*d.mbw && p1.Y >= 16*d.mbh { - return - } - } - m := image.NewYCbCr(image.Rect(0, 0, 16*d.mbw, 16*d.mbh), image.YCbCrSubsampleRatio420) - d.img = m.SubImage(image.Rect(0, 0, d.frameHeader.Width, d.frameHeader.Height)).(*image.YCbCr) - d.perMBFilterParams = make([]filterParam, d.mbw*d.mbh) - d.upMB = make([]mb, d.mbw) -} - -// parseSegmentHeader parses the segment header, as specified in section 9.3. -func (d *Decoder) parseSegmentHeader() { - d.segmentHeader.useSegment = d.fp.readBit(uniformProb) - if !d.segmentHeader.useSegment { - d.segmentHeader.updateMap = false - return - } - d.segmentHeader.updateMap = d.fp.readBit(uniformProb) - if d.fp.readBit(uniformProb) { - d.segmentHeader.relativeDelta = !d.fp.readBit(uniformProb) - for i := range d.segmentHeader.quantizer { - d.segmentHeader.quantizer[i] = int8(d.fp.readOptionalInt(uniformProb, 7)) - } - for i := range d.segmentHeader.filterStrength { - d.segmentHeader.filterStrength[i] = int8(d.fp.readOptionalInt(uniformProb, 6)) - } - } - if !d.segmentHeader.updateMap { - return - } - for i := range d.segmentHeader.prob { - if d.fp.readBit(uniformProb) { - d.segmentHeader.prob[i] = uint8(d.fp.readUint(uniformProb, 8)) - } else { - d.segmentHeader.prob[i] = 0xff - } - } -} - -// parseFilterHeader parses the filter header, as specified in section 9.4. -func (d *Decoder) parseFilterHeader() { - d.filterHeader.simple = d.fp.readBit(uniformProb) - d.filterHeader.level = int8(d.fp.readUint(uniformProb, 6)) - d.filterHeader.sharpness = uint8(d.fp.readUint(uniformProb, 3)) - d.filterHeader.useLFDelta = d.fp.readBit(uniformProb) - if d.filterHeader.useLFDelta && d.fp.readBit(uniformProb) { - for i := range d.filterHeader.refLFDelta { - d.filterHeader.refLFDelta[i] = int8(d.fp.readOptionalInt(uniformProb, 6)) - } - for i := range d.filterHeader.modeLFDelta { - d.filterHeader.modeLFDelta[i] = int8(d.fp.readOptionalInt(uniformProb, 6)) - } - } - if d.filterHeader.level == 0 { - return - } - if d.segmentHeader.useSegment { - for i := range d.filterHeader.perSegmentLevel { - strength := d.segmentHeader.filterStrength[i] - if d.segmentHeader.relativeDelta { - strength += d.filterHeader.level - } - d.filterHeader.perSegmentLevel[i] = strength - } - } else { - d.filterHeader.perSegmentLevel[0] = d.filterHeader.level - } - d.computeFilterParams() -} - -// parseOtherPartitions parses the other partitions, as specified in section 9.5. -func (d *Decoder) parseOtherPartitions() error { - const maxNOP = 1 << 3 - var partLens [maxNOP]int - d.nOP = 1 << d.fp.readUint(uniformProb, 2) - - // The final partition length is implied by the remaining chunk data - // (d.r.n) and the other d.nOP-1 partition lengths. Those d.nOP-1 partition - // lengths are stored as 24-bit uints, i.e. up to 16 MiB per partition. - n := 3 * (d.nOP - 1) - partLens[d.nOP-1] = d.r.n - n - if partLens[d.nOP-1] < 0 { - return io.ErrUnexpectedEOF - } - if n > 0 { - buf := make([]byte, n) - if err := d.r.ReadFull(buf); err != nil { - return err - } - for i := 0; i < d.nOP-1; i++ { - pl := int(buf[3*i+0]) | int(buf[3*i+1])<<8 | int(buf[3*i+2])<<16 - if pl > partLens[d.nOP-1] { - return io.ErrUnexpectedEOF - } - partLens[i] = pl - partLens[d.nOP-1] -= pl - } - } - - // We check if the final partition length can also fit into a 24-bit uint. - // Strictly speaking, this isn't part of the spec, but it guards against a - // malicious WEBP image that is too large to ReadFull the encoded DCT - // coefficients into memory, whether that's because the actual WEBP file is - // too large, or whether its RIFF metadata lists too large a chunk. - if 1<<24 <= partLens[d.nOP-1] { - return errors.New("vp8: too much data to decode") - } - - buf := make([]byte, d.r.n) - if err := d.r.ReadFull(buf); err != nil { - return err - } - for i, pl := range partLens { - if i == d.nOP { - break - } - d.op[i].init(buf[:pl]) - buf = buf[pl:] - } - return nil -} - -// parseOtherHeaders parses header information other than the frame header. -func (d *Decoder) parseOtherHeaders() error { - // Initialize and parse the first partition. - firstPartition := make([]byte, d.frameHeader.FirstPartitionLen) - if err := d.r.ReadFull(firstPartition); err != nil { - return err - } - d.fp.init(firstPartition) - if d.frameHeader.KeyFrame { - // Read and ignore the color space and pixel clamp values. They are - // specified in section 9.2, but are unimplemented. - d.fp.readBit(uniformProb) - d.fp.readBit(uniformProb) - } - d.parseSegmentHeader() - d.parseFilterHeader() - if err := d.parseOtherPartitions(); err != nil { - return err - } - d.parseQuant() - if !d.frameHeader.KeyFrame { - // Golden and AltRef frames are specified in section 9.7. - // TODO(nigeltao): implement. Note that they are only used for video, not still images. - return errors.New("vp8: Golden / AltRef frames are not implemented") - } - // Read and ignore the refreshLastFrameBuffer bit, specified in section 9.8. - // It applies only to video, and not still images. - d.fp.readBit(uniformProb) - d.parseTokenProb() - d.useSkipProb = d.fp.readBit(uniformProb) - if d.useSkipProb { - d.skipProb = uint8(d.fp.readUint(uniformProb, 8)) - } - if d.fp.unexpectedEOF { - return io.ErrUnexpectedEOF - } - return nil -} - -// DecodeFrame decodes the frame and returns it as an YCbCr image. -// The image's contents are valid up until the next call to Decoder.Init. -func (d *Decoder) DecodeFrame() (*image.YCbCr, error) { - d.ensureImg() - if err := d.parseOtherHeaders(); err != nil { - return nil, err - } - // Reconstruct the rows. - for mbx := 0; mbx < d.mbw; mbx++ { - d.upMB[mbx] = mb{} - } - for mby := 0; mby < d.mbh; mby++ { - d.leftMB = mb{} - for mbx := 0; mbx < d.mbw; mbx++ { - skip := d.reconstruct(mbx, mby) - fs := d.filterParams[d.segment][btou(!d.usePredY16)] - fs.inner = fs.inner || !skip - d.perMBFilterParams[d.mbw*mby+mbx] = fs - } - } - if d.fp.unexpectedEOF { - return nil, io.ErrUnexpectedEOF - } - for i := 0; i < d.nOP; i++ { - if d.op[i].unexpectedEOF { - return nil, io.ErrUnexpectedEOF - } - } - // Apply the loop filter. - // - // Even if we are using per-segment levels, section 15 says that "loop - // filtering must be skipped entirely if loop_filter_level at either the - // frame header level or macroblock override level is 0". - if d.filterHeader.level != 0 { - if d.filterHeader.simple { - d.simpleFilter() - } else { - d.normalFilter() - } - } - return d.img, nil -} |