| // 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) Write(data []byte) (int, error) { |
| if b.e.err != nil { |
| return 0, b.e.err |
| } |
| if len(data) == 0 { |
| return 0, nil |
| } |
| total := 0 |
| for total < len(data) { |
| n := copy(b.e.buf[1:256], data[total:]) |
| total += n |
| b.e.buf[0] = uint8(n) |
| |
| _, b.e.err = b.e.w.Write(b.e.buf[:n+1]) |
| if b.e.err != nil { |
| return 0, b.e.err |
| } |
| } |
| return total, b.e.err |
| } |
| |
| 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.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") |
| } |
| n := log2Lookup[size] |
| for i := 0; i < n; i++ { |
| if i < len(p) { |
| c := p[i] |
| if c == nil { |
| return 0, errors.New("gif: cannot encode color table with nil entries") |
| } |
| r, g, b, _ := c.RGBA() |
| dst[3*i+0] = uint8(r >> 8) |
| dst[3*i+1] = uint8(g >> 8) |
| dst[3*i+2] = uint8(b >> 8) |
| } else { |
| // Pad with black. |
| dst[3*i+0] = 0x00 |
| dst[3*i+1] = 0x00 |
| dst[3*i+2] = 0x00 |
| } |
| } |
| return 3 * n, nil |
| } |
| |
| 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]) |
| |
| paddedSize := log2(len(pm.Palette)) // Size of Local Color Table: 2^(1+n). |
| if ct, err := encodeColorTable(e.localColorTable[:], pm.Palette, paddedSize); err != nil { |
| if e.err == nil { |
| e.err = err |
| } |
| return |
| } else if ct != e.globalCT || !bytes.Equal(e.globalColorTable[:ct], e.localColorTable[:ct]) { |
| // Use a local color table. |
| e.writeByte(fColorTable | uint8(paddedSize)) |
| e.write(e.localColorTable[:ct]) |
| } else { |
| // Use the global color table. |
| e.writeByte(0) |
| } |
| |
| litWidth := paddedSize + 1 |
| if litWidth < 2 { |
| litWidth = 2 |
| } |
| e.writeByte(uint8(litWidth)) // LZW Minimum Code Size. |
| |
| lzww := lzw.NewWriter(blockWriter{e: e}, 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() |
| e.writeByte(0x00) // Block Terminator. |
| } |
| |
| // 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") |
| } |
| if g.LoopCount < 0 { |
| g.LoopCount = 0 |
| } |
| |
| 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, ok := m.(*image.Paletted) |
| if !ok || len(pm.Palette) > opts.NumColors { |
| // 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, image.ZP) |
| } |
| |
| // 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(), |
| }, |
| }) |
| } |