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-rw-r--r--src/image/gif/writer.go477
1 files changed, 477 insertions, 0 deletions
diff --git a/src/image/gif/writer.go b/src/image/gif/writer.go
new file mode 100644
index 0000000..7220446
--- /dev/null
+++ b/src/image/gif/writer.go
@@ -0,0 +1,477 @@
+// Copyright 2013 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 gif
+
+import (
+ "bufio"
+ "bytes"
+ "compress/lzw"
+ "errors"
+ "image"
+ "image/color"
+ "image/color/palette"
+ "image/draw"
+ "io"
+)
+
+// Graphic control extension fields.
+const (
+ gcLabel = 0xF9
+ gcBlockSize = 0x04
+)
+
+var log2Lookup = [8]int{2, 4, 8, 16, 32, 64, 128, 256}
+
+func log2(x int) int {
+ for i, v := range log2Lookup {
+ if x <= v {
+ return i
+ }
+ }
+ return -1
+}
+
+// Little-endian.
+func writeUint16(b []uint8, u uint16) {
+ b[0] = uint8(u)
+ b[1] = uint8(u >> 8)
+}
+
+// writer is a buffered writer.
+type writer interface {
+ Flush() error
+ io.Writer
+ io.ByteWriter
+}
+
+// encoder encodes an image to the GIF format.
+type encoder struct {
+ // w is the writer to write to. err is the first error encountered during
+ // writing. All attempted writes after the first error become no-ops.
+ w writer
+ err error
+ // g is a reference to the data that is being encoded.
+ g GIF
+ // globalCT is the size in bytes of the global color table.
+ globalCT int
+ // buf is a scratch buffer. It must be at least 256 for the blockWriter.
+ buf [256]byte
+ globalColorTable [3 * 256]byte
+ localColorTable [3 * 256]byte
+}
+
+// blockWriter writes the block structure of GIF image data, which
+// comprises (n, (n bytes)) blocks, with 1 <= n <= 255. It is the
+// writer given to the LZW encoder, which is thus immune to the
+// blocking.
+type blockWriter struct {
+ e *encoder
+}
+
+func (b blockWriter) setup() {
+ b.e.buf[0] = 0
+}
+
+func (b blockWriter) Flush() error {
+ return b.e.err
+}
+
+func (b blockWriter) WriteByte(c byte) error {
+ if b.e.err != nil {
+ return b.e.err
+ }
+
+ // Append c to buffered sub-block.
+ b.e.buf[0]++
+ b.e.buf[b.e.buf[0]] = c
+ if b.e.buf[0] < 255 {
+ return nil
+ }
+
+ // Flush block
+ b.e.write(b.e.buf[:256])
+ b.e.buf[0] = 0
+ return b.e.err
+}
+
+// blockWriter must be an io.Writer for lzw.NewWriter, but this is never
+// actually called.
+func (b blockWriter) Write(data []byte) (int, error) {
+ for i, c := range data {
+ if err := b.WriteByte(c); err != nil {
+ return i, err
+ }
+ }
+ return len(data), nil
+}
+
+func (b blockWriter) close() {
+ // Write the block terminator (0x00), either by itself, or along with a
+ // pending sub-block.
+ if b.e.buf[0] == 0 {
+ b.e.writeByte(0)
+ } else {
+ n := uint(b.e.buf[0])
+ b.e.buf[n+1] = 0
+ b.e.write(b.e.buf[:n+2])
+ }
+ b.e.flush()
+}
+
+func (e *encoder) flush() {
+ if e.err != nil {
+ return
+ }
+ e.err = e.w.Flush()
+}
+
+func (e *encoder) write(p []byte) {
+ if e.err != nil {
+ return
+ }
+ _, e.err = e.w.Write(p)
+}
+
+func (e *encoder) writeByte(b byte) {
+ if e.err != nil {
+ return
+ }
+ e.err = e.w.WriteByte(b)
+}
+
+func (e *encoder) writeHeader() {
+ if e.err != nil {
+ return
+ }
+ _, e.err = io.WriteString(e.w, "GIF89a")
+ if e.err != nil {
+ return
+ }
+
+ // Logical screen width and height.
+ writeUint16(e.buf[0:2], uint16(e.g.Config.Width))
+ writeUint16(e.buf[2:4], uint16(e.g.Config.Height))
+ e.write(e.buf[:4])
+
+ if p, ok := e.g.Config.ColorModel.(color.Palette); ok && len(p) > 0 {
+ paddedSize := log2(len(p)) // Size of Global Color Table: 2^(1+n).
+ e.buf[0] = fColorTable | uint8(paddedSize)
+ e.buf[1] = e.g.BackgroundIndex
+ e.buf[2] = 0x00 // Pixel Aspect Ratio.
+ e.write(e.buf[:3])
+ var err error
+ e.globalCT, err = encodeColorTable(e.globalColorTable[:], p, paddedSize)
+ if err != nil && e.err == nil {
+ e.err = err
+ return
+ }
+ e.write(e.globalColorTable[:e.globalCT])
+ } else {
+ // All frames have a local color table, so a global color table
+ // is not needed.
+ e.buf[0] = 0x00
+ e.buf[1] = 0x00 // Background Color Index.
+ e.buf[2] = 0x00 // Pixel Aspect Ratio.
+ e.write(e.buf[:3])
+ }
+
+ // Add animation info if necessary.
+ if len(e.g.Image) > 1 && e.g.LoopCount >= 0 {
+ e.buf[0] = 0x21 // Extension Introducer.
+ e.buf[1] = 0xff // Application Label.
+ e.buf[2] = 0x0b // Block Size.
+ e.write(e.buf[:3])
+ _, err := io.WriteString(e.w, "NETSCAPE2.0") // Application Identifier.
+ if err != nil && e.err == nil {
+ e.err = err
+ return
+ }
+ e.buf[0] = 0x03 // Block Size.
+ e.buf[1] = 0x01 // Sub-block Index.
+ writeUint16(e.buf[2:4], uint16(e.g.LoopCount))
+ e.buf[4] = 0x00 // Block Terminator.
+ e.write(e.buf[:5])
+ }
+}
+
+func encodeColorTable(dst []byte, p color.Palette, size int) (int, error) {
+ if uint(size) >= uint(len(log2Lookup)) {
+ return 0, errors.New("gif: cannot encode color table with more than 256 entries")
+ }
+ for i, c := range p {
+ if c == nil {
+ return 0, errors.New("gif: cannot encode color table with nil entries")
+ }
+ var r, g, b uint8
+ // It is most likely that the palette is full of color.RGBAs, so they
+ // get a fast path.
+ if rgba, ok := c.(color.RGBA); ok {
+ r, g, b = rgba.R, rgba.G, rgba.B
+ } else {
+ rr, gg, bb, _ := c.RGBA()
+ r, g, b = uint8(rr>>8), uint8(gg>>8), uint8(bb>>8)
+ }
+ dst[3*i+0] = r
+ dst[3*i+1] = g
+ dst[3*i+2] = b
+ }
+ n := log2Lookup[size]
+ if n > len(p) {
+ // Pad with black.
+ fill := dst[3*len(p) : 3*n]
+ for i := range fill {
+ fill[i] = 0
+ }
+ }
+ return 3 * n, nil
+}
+
+func (e *encoder) colorTablesMatch(localLen, transparentIndex int) bool {
+ localSize := 3 * localLen
+ if transparentIndex >= 0 {
+ trOff := 3 * transparentIndex
+ return bytes.Equal(e.globalColorTable[:trOff], e.localColorTable[:trOff]) &&
+ bytes.Equal(e.globalColorTable[trOff+3:localSize], e.localColorTable[trOff+3:localSize])
+ }
+ return bytes.Equal(e.globalColorTable[:localSize], e.localColorTable[:localSize])
+}
+
+func (e *encoder) writeImageBlock(pm *image.Paletted, delay int, disposal byte) {
+ if e.err != nil {
+ return
+ }
+
+ if len(pm.Palette) == 0 {
+ e.err = errors.New("gif: cannot encode image block with empty palette")
+ return
+ }
+
+ b := pm.Bounds()
+ if b.Min.X < 0 || b.Max.X >= 1<<16 || b.Min.Y < 0 || b.Max.Y >= 1<<16 {
+ e.err = errors.New("gif: image block is too large to encode")
+ return
+ }
+ if !b.In(image.Rectangle{Max: image.Point{e.g.Config.Width, e.g.Config.Height}}) {
+ e.err = errors.New("gif: image block is out of bounds")
+ return
+ }
+
+ transparentIndex := -1
+ for i, c := range pm.Palette {
+ if c == nil {
+ e.err = errors.New("gif: cannot encode color table with nil entries")
+ return
+ }
+ if _, _, _, a := c.RGBA(); a == 0 {
+ transparentIndex = i
+ break
+ }
+ }
+
+ if delay > 0 || disposal != 0 || transparentIndex != -1 {
+ e.buf[0] = sExtension // Extension Introducer.
+ e.buf[1] = gcLabel // Graphic Control Label.
+ e.buf[2] = gcBlockSize // Block Size.
+ if transparentIndex != -1 {
+ e.buf[3] = 0x01 | disposal<<2
+ } else {
+ e.buf[3] = 0x00 | disposal<<2
+ }
+ writeUint16(e.buf[4:6], uint16(delay)) // Delay Time (1/100ths of a second)
+
+ // Transparent color index.
+ if transparentIndex != -1 {
+ e.buf[6] = uint8(transparentIndex)
+ } else {
+ e.buf[6] = 0x00
+ }
+ e.buf[7] = 0x00 // Block Terminator.
+ e.write(e.buf[:8])
+ }
+ e.buf[0] = sImageDescriptor
+ writeUint16(e.buf[1:3], uint16(b.Min.X))
+ writeUint16(e.buf[3:5], uint16(b.Min.Y))
+ writeUint16(e.buf[5:7], uint16(b.Dx()))
+ writeUint16(e.buf[7:9], uint16(b.Dy()))
+ e.write(e.buf[:9])
+
+ // To determine whether or not this frame's palette is the same as the
+ // global palette, we can check a couple things. First, do they actually
+ // point to the same []color.Color? If so, they are equal so long as the
+ // frame's palette is not longer than the global palette...
+ paddedSize := log2(len(pm.Palette)) // Size of Local Color Table: 2^(1+n).
+ if gp, ok := e.g.Config.ColorModel.(color.Palette); ok && len(pm.Palette) <= len(gp) && &gp[0] == &pm.Palette[0] {
+ e.writeByte(0) // Use the global color table.
+ } else {
+ ct, err := encodeColorTable(e.localColorTable[:], pm.Palette, paddedSize)
+ if err != nil {
+ if e.err == nil {
+ e.err = err
+ }
+ return
+ }
+ // This frame's palette is not the very same slice as the global
+ // palette, but it might be a copy, possibly with one value turned into
+ // transparency by DecodeAll.
+ if ct <= e.globalCT && e.colorTablesMatch(len(pm.Palette), transparentIndex) {
+ e.writeByte(0) // Use the global color table.
+ } else {
+ // Use a local color table.
+ e.writeByte(fColorTable | uint8(paddedSize))
+ e.write(e.localColorTable[:ct])
+ }
+ }
+
+ litWidth := paddedSize + 1
+ if litWidth < 2 {
+ litWidth = 2
+ }
+ e.writeByte(uint8(litWidth)) // LZW Minimum Code Size.
+
+ bw := blockWriter{e: e}
+ bw.setup()
+ lzww := lzw.NewWriter(bw, lzw.LSB, litWidth)
+ if dx := b.Dx(); dx == pm.Stride {
+ _, e.err = lzww.Write(pm.Pix[:dx*b.Dy()])
+ if e.err != nil {
+ lzww.Close()
+ return
+ }
+ } else {
+ for i, y := 0, b.Min.Y; y < b.Max.Y; i, y = i+pm.Stride, y+1 {
+ _, e.err = lzww.Write(pm.Pix[i : i+dx])
+ if e.err != nil {
+ lzww.Close()
+ return
+ }
+ }
+ }
+ lzww.Close() // flush to bw
+ bw.close() // flush to e.w
+}
+
+// Options are the encoding parameters.
+type Options struct {
+ // NumColors is the maximum number of colors used in the image.
+ // It ranges from 1 to 256.
+ NumColors int
+
+ // Quantizer is used to produce a palette with size NumColors.
+ // palette.Plan9 is used in place of a nil Quantizer.
+ Quantizer draw.Quantizer
+
+ // Drawer is used to convert the source image to the desired palette.
+ // draw.FloydSteinberg is used in place of a nil Drawer.
+ Drawer draw.Drawer
+}
+
+// EncodeAll writes the images in g to w in GIF format with the
+// given loop count and delay between frames.
+func EncodeAll(w io.Writer, g *GIF) error {
+ if len(g.Image) == 0 {
+ return errors.New("gif: must provide at least one image")
+ }
+
+ if len(g.Image) != len(g.Delay) {
+ return errors.New("gif: mismatched image and delay lengths")
+ }
+
+ e := encoder{g: *g}
+ // The GIF.Disposal, GIF.Config and GIF.BackgroundIndex fields were added
+ // in Go 1.5. Valid Go 1.4 code, such as when the Disposal field is omitted
+ // in a GIF struct literal, should still produce valid GIFs.
+ if e.g.Disposal != nil && len(e.g.Image) != len(e.g.Disposal) {
+ return errors.New("gif: mismatched image and disposal lengths")
+ }
+ if e.g.Config == (image.Config{}) {
+ p := g.Image[0].Bounds().Max
+ e.g.Config.Width = p.X
+ e.g.Config.Height = p.Y
+ } else if e.g.Config.ColorModel != nil {
+ if _, ok := e.g.Config.ColorModel.(color.Palette); !ok {
+ return errors.New("gif: GIF color model must be a color.Palette")
+ }
+ }
+
+ if ww, ok := w.(writer); ok {
+ e.w = ww
+ } else {
+ e.w = bufio.NewWriter(w)
+ }
+
+ e.writeHeader()
+ for i, pm := range g.Image {
+ disposal := uint8(0)
+ if g.Disposal != nil {
+ disposal = g.Disposal[i]
+ }
+ e.writeImageBlock(pm, g.Delay[i], disposal)
+ }
+ e.writeByte(sTrailer)
+ e.flush()
+ return e.err
+}
+
+// Encode writes the Image m to w in GIF format.
+func Encode(w io.Writer, m image.Image, o *Options) error {
+ // Check for bounds and size restrictions.
+ b := m.Bounds()
+ if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
+ return errors.New("gif: image is too large to encode")
+ }
+
+ opts := Options{}
+ if o != nil {
+ opts = *o
+ }
+ if opts.NumColors < 1 || 256 < opts.NumColors {
+ opts.NumColors = 256
+ }
+ if opts.Drawer == nil {
+ opts.Drawer = draw.FloydSteinberg
+ }
+
+ pm, _ := m.(*image.Paletted)
+ if pm == nil {
+ if cp, ok := m.ColorModel().(color.Palette); ok {
+ pm = image.NewPaletted(b, cp)
+ for y := b.Min.Y; y < b.Max.Y; y++ {
+ for x := b.Min.X; x < b.Max.X; x++ {
+ pm.Set(x, y, cp.Convert(m.At(x, y)))
+ }
+ }
+ }
+ }
+ if pm == nil || len(pm.Palette) > opts.NumColors {
+ // Set pm to be a palettedized copy of m, including its bounds, which
+ // might not start at (0, 0).
+ //
+ // TODO: Pick a better sub-sample of the Plan 9 palette.
+ pm = image.NewPaletted(b, palette.Plan9[:opts.NumColors])
+ if opts.Quantizer != nil {
+ pm.Palette = opts.Quantizer.Quantize(make(color.Palette, 0, opts.NumColors), m)
+ }
+ opts.Drawer.Draw(pm, b, m, b.Min)
+ }
+
+ // When calling Encode instead of EncodeAll, the single-frame image is
+ // translated such that its top-left corner is (0, 0), so that the single
+ // frame completely fills the overall GIF's bounds.
+ if pm.Rect.Min != (image.Point{}) {
+ dup := *pm
+ dup.Rect = dup.Rect.Sub(dup.Rect.Min)
+ pm = &dup
+ }
+
+ return EncodeAll(w, &GIF{
+ Image: []*image.Paletted{pm},
+ Delay: []int{0},
+ Config: image.Config{
+ ColorModel: pm.Palette,
+ Width: b.Dx(),
+ Height: b.Dy(),
+ },
+ })
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-24 21:54:44 +0000