2013-11-06 20:49:01 +01:00
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// Copyright 2013 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 gif
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import (
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"bufio"
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"bytes"
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2013-11-06 20:49:01 +01:00
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"compress/lzw"
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"errors"
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"image"
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"image/color"
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"image/color/palette"
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"image/draw"
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"io"
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)
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// Graphic control extension fields.
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const (
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gcLabel = 0xF9
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gcBlockSize = 0x04
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)
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var log2Lookup = [8]int{2, 4, 8, 16, 32, 64, 128, 256}
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func log2(x int) int {
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for i, v := range log2Lookup {
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if x <= v {
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return i
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}
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}
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return -1
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}
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// Little-endian.
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func writeUint16(b []uint8, u uint16) {
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b[0] = uint8(u)
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b[1] = uint8(u >> 8)
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}
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// writer is a buffered writer.
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type writer interface {
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Flush() error
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io.Writer
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io.ByteWriter
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}
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// encoder encodes an image to the GIF format.
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type encoder struct {
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// w is the writer to write to. err is the first error encountered during
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// writing. All attempted writes after the first error become no-ops.
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w writer
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err error
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// g is a reference to the data that is being encoded.
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g GIF
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// globalCT is the size in bytes of the global color table.
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globalCT int
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// buf is a scratch buffer. It must be at least 256 for the blockWriter.
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buf [256]byte
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globalColorTable [3 * 256]byte
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localColorTable [3 * 256]byte
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}
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// blockWriter writes the block structure of GIF image data, which
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// comprises (n, (n bytes)) blocks, with 1 <= n <= 255. It is the
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// writer given to the LZW encoder, which is thus immune to the
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// blocking.
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type blockWriter struct {
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e *encoder
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}
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func (b blockWriter) Write(data []byte) (int, error) {
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if b.e.err != nil {
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return 0, b.e.err
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}
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if len(data) == 0 {
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return 0, nil
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}
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total := 0
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for total < len(data) {
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n := copy(b.e.buf[1:256], data[total:])
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total += n
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b.e.buf[0] = uint8(n)
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2016-02-03 22:58:02 +01:00
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_, b.e.err = b.e.w.Write(b.e.buf[:n+1])
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if b.e.err != nil {
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return 0, b.e.err
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}
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}
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return total, b.e.err
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}
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func (e *encoder) flush() {
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if e.err != nil {
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return
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}
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e.err = e.w.Flush()
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}
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func (e *encoder) write(p []byte) {
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if e.err != nil {
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return
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}
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_, e.err = e.w.Write(p)
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}
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func (e *encoder) writeByte(b byte) {
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if e.err != nil {
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return
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}
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e.err = e.w.WriteByte(b)
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}
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func (e *encoder) writeHeader() {
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if e.err != nil {
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return
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}
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_, e.err = io.WriteString(e.w, "GIF89a")
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if e.err != nil {
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return
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}
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// Logical screen width and height.
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writeUint16(e.buf[0:2], uint16(e.g.Config.Width))
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writeUint16(e.buf[2:4], uint16(e.g.Config.Height))
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e.write(e.buf[:4])
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if p, ok := e.g.Config.ColorModel.(color.Palette); ok && len(p) > 0 {
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paddedSize := log2(len(p)) // Size of Global Color Table: 2^(1+n).
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e.buf[0] = fColorTable | uint8(paddedSize)
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e.buf[1] = e.g.BackgroundIndex
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e.buf[2] = 0x00 // Pixel Aspect Ratio.
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e.write(e.buf[:3])
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e.globalCT = encodeColorTable(e.globalColorTable[:], p, paddedSize)
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e.write(e.globalColorTable[:e.globalCT])
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} else {
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// All frames have a local color table, so a global color table
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// is not needed.
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e.buf[0] = 0x00
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e.buf[1] = 0x00 // Background Color Index.
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e.buf[2] = 0x00 // Pixel Aspect Ratio.
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e.write(e.buf[:3])
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}
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// Add animation info if necessary.
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if len(e.g.Image) > 1 {
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e.buf[0] = 0x21 // Extension Introducer.
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e.buf[1] = 0xff // Application Label.
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e.buf[2] = 0x0b // Block Size.
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e.write(e.buf[:3])
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_, e.err = io.WriteString(e.w, "NETSCAPE2.0") // Application Identifier.
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if e.err != nil {
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return
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}
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e.buf[0] = 0x03 // Block Size.
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e.buf[1] = 0x01 // Sub-block Index.
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writeUint16(e.buf[2:4], uint16(e.g.LoopCount))
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e.buf[4] = 0x00 // Block Terminator.
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e.write(e.buf[:5])
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}
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}
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func encodeColorTable(dst []byte, p color.Palette, size int) int {
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n := log2Lookup[size]
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for i := 0; i < n; i++ {
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if i < len(p) {
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r, g, b, _ := p[i].RGBA()
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dst[3*i+0] = uint8(r >> 8)
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dst[3*i+1] = uint8(g >> 8)
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dst[3*i+2] = uint8(b >> 8)
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} else {
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// Pad with black.
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dst[3*i+0] = 0x00
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dst[3*i+1] = 0x00
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dst[3*i+2] = 0x00
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}
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}
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return 3 * n
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}
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func (e *encoder) writeImageBlock(pm *image.Paletted, delay int, disposal byte) {
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if e.err != nil {
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return
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}
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if len(pm.Palette) == 0 {
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e.err = errors.New("gif: cannot encode image block with empty palette")
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return
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}
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b := pm.Bounds()
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if b.Min.X < 0 || b.Max.X >= 1<<16 || b.Min.Y < 0 || b.Max.Y >= 1<<16 {
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e.err = errors.New("gif: image block is too large to encode")
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return
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}
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if !b.In(image.Rectangle{Max: image.Point{e.g.Config.Width, e.g.Config.Height}}) {
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e.err = errors.New("gif: image block is out of bounds")
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return
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}
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transparentIndex := -1
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for i, c := range pm.Palette {
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if _, _, _, a := c.RGBA(); a == 0 {
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transparentIndex = i
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break
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}
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}
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if delay > 0 || disposal != 0 || transparentIndex != -1 {
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e.buf[0] = sExtension // Extension Introducer.
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e.buf[1] = gcLabel // Graphic Control Label.
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e.buf[2] = gcBlockSize // Block Size.
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if transparentIndex != -1 {
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e.buf[3] = 0x01 | disposal<<2
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} else {
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e.buf[3] = 0x00 | disposal<<2
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}
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writeUint16(e.buf[4:6], uint16(delay)) // Delay Time (1/100ths of a second)
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// Transparent color index.
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if transparentIndex != -1 {
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e.buf[6] = uint8(transparentIndex)
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} else {
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e.buf[6] = 0x00
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}
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e.buf[7] = 0x00 // Block Terminator.
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e.write(e.buf[:8])
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}
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e.buf[0] = sImageDescriptor
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writeUint16(e.buf[1:3], uint16(b.Min.X))
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writeUint16(e.buf[3:5], uint16(b.Min.Y))
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writeUint16(e.buf[5:7], uint16(b.Dx()))
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writeUint16(e.buf[7:9], uint16(b.Dy()))
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e.write(e.buf[:9])
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paddedSize := log2(len(pm.Palette)) // Size of Local Color Table: 2^(1+n).
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ct := encodeColorTable(e.localColorTable[:], pm.Palette, paddedSize)
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if ct != e.globalCT || !bytes.Equal(e.globalColorTable[:ct], e.localColorTable[:ct]) {
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// Use a local color table.
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e.writeByte(fColorTable | uint8(paddedSize))
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e.write(e.localColorTable[:ct])
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} else {
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// Use the global color table.
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e.writeByte(0)
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}
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litWidth := paddedSize + 1
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if litWidth < 2 {
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litWidth = 2
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}
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e.writeByte(uint8(litWidth)) // LZW Minimum Code Size.
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lzww := lzw.NewWriter(blockWriter{e: e}, lzw.LSB, litWidth)
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if dx := b.Dx(); dx == pm.Stride {
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_, e.err = lzww.Write(pm.Pix)
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if e.err != nil {
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lzww.Close()
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return
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}
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} else {
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for i, y := 0, b.Min.Y; y < b.Max.Y; i, y = i+pm.Stride, y+1 {
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_, e.err = lzww.Write(pm.Pix[i : i+dx])
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if e.err != nil {
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lzww.Close()
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return
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}
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}
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}
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lzww.Close()
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e.writeByte(0x00) // Block Terminator.
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}
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// Options are the encoding parameters.
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type Options struct {
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// NumColors is the maximum number of colors used in the image.
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// It ranges from 1 to 256.
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NumColors int
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// Quantizer is used to produce a palette with size NumColors.
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// palette.Plan9 is used in place of a nil Quantizer.
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Quantizer draw.Quantizer
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// Drawer is used to convert the source image to the desired palette.
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// draw.FloydSteinberg is used in place of a nil Drawer.
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Drawer draw.Drawer
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}
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// EncodeAll writes the images in g to w in GIF format with the
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// given loop count and delay between frames.
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func EncodeAll(w io.Writer, g *GIF) error {
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if len(g.Image) == 0 {
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return errors.New("gif: must provide at least one image")
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}
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if len(g.Image) != len(g.Delay) {
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return errors.New("gif: mismatched image and delay lengths")
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}
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if g.LoopCount < 0 {
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g.LoopCount = 0
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}
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e := encoder{g: *g}
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// The GIF.Disposal, GIF.Config and GIF.BackgroundIndex fields were added
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// in Go 1.5. Valid Go 1.4 code, such as when the Disposal field is omitted
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// in a GIF struct literal, should still produce valid GIFs.
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if e.g.Disposal != nil && len(e.g.Image) != len(e.g.Disposal) {
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return errors.New("gif: mismatched image and disposal lengths")
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}
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if e.g.Config == (image.Config{}) {
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p := g.Image[0].Bounds().Max
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e.g.Config.Width = p.X
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e.g.Config.Height = p.Y
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} else if e.g.Config.ColorModel != nil {
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if _, ok := e.g.Config.ColorModel.(color.Palette); !ok {
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return errors.New("gif: GIF color model must be a color.Palette")
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}
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}
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if ww, ok := w.(writer); ok {
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e.w = ww
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} else {
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e.w = bufio.NewWriter(w)
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}
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e.writeHeader()
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for i, pm := range g.Image {
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disposal := uint8(0)
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if g.Disposal != nil {
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disposal = g.Disposal[i]
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}
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e.writeImageBlock(pm, g.Delay[i], disposal)
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}
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e.writeByte(sTrailer)
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e.flush()
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return e.err
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}
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// Encode writes the Image m to w in GIF format.
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func Encode(w io.Writer, m image.Image, o *Options) error {
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// Check for bounds and size restrictions.
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b := m.Bounds()
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if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
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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)
|
|
|
|
}
|
|
|
|
|
2015-10-31 01:59:47 +01:00
|
|
|
// 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
|
|
|
|
}
|
|
|
|
|
2013-11-06 20:49:01 +01:00
|
|
|
return EncodeAll(w, &GIF{
|
|
|
|
Image: []*image.Paletted{pm},
|
|
|
|
Delay: []int{0},
|
2015-10-31 01:59:47 +01:00
|
|
|
Config: image.Config{
|
|
|
|
ColorModel: pm.Palette,
|
|
|
|
Width: b.Dx(),
|
|
|
|
Height: b.Dy(),
|
|
|
|
},
|
2013-11-06 20:49:01 +01:00
|
|
|
})
|
|
|
|
}
|