477 lines
12 KiB
Go
477 lines
12 KiB
Go
// 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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"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) setup() {
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b.e.buf[0] = 0
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}
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func (b blockWriter) Flush() error {
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return b.e.err
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}
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func (b blockWriter) WriteByte(c byte) error {
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if b.e.err != nil {
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return b.e.err
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}
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// Append c to buffered sub-block.
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b.e.buf[0]++
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b.e.buf[b.e.buf[0]] = c
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if b.e.buf[0] < 255 {
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return nil
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}
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// Flush block
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b.e.write(b.e.buf[:256])
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b.e.buf[0] = 0
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return b.e.err
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}
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// blockWriter must be an io.Writer for lzw.NewWriter, but this is never
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// actually called.
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func (b blockWriter) Write(data []byte) (int, error) {
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for i, c := range data {
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if err := b.WriteByte(c); err != nil {
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return i, err
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}
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}
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return len(data), nil
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}
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func (b blockWriter) close() {
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// Write the block terminator (0x00), either by itself, or along with a
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// pending sub-block.
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if b.e.buf[0] == 0 {
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b.e.writeByte(0)
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} else {
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n := uint(b.e.buf[0])
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b.e.buf[n+1] = 0
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b.e.write(b.e.buf[:n+2])
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}
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b.e.flush()
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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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var err error
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e.globalCT, err = encodeColorTable(e.globalColorTable[:], p, paddedSize)
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if err != nil && e.err == nil {
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e.err = err
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return
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}
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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 && e.g.LoopCount >= 0 {
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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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_, err := io.WriteString(e.w, "NETSCAPE2.0") // Application Identifier.
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if err != nil && e.err == nil {
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e.err = err
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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, error) {
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if uint(size) >= uint(len(log2Lookup)) {
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return 0, errors.New("gif: cannot encode color table with more than 256 entries")
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}
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for i, c := range p {
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if c == nil {
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return 0, errors.New("gif: cannot encode color table with nil entries")
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}
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var r, g, b uint8
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// It is most likely that the palette is full of color.RGBAs, so they
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// get a fast path.
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if rgba, ok := c.(color.RGBA); ok {
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r, g, b = rgba.R, rgba.G, rgba.B
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} else {
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rr, gg, bb, _ := c.RGBA()
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r, g, b = uint8(rr>>8), uint8(gg>>8), uint8(bb>>8)
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}
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dst[3*i+0] = r
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dst[3*i+1] = g
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dst[3*i+2] = b
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}
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n := log2Lookup[size]
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if n > len(p) {
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// Pad with black.
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fill := dst[3*len(p) : 3*n]
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for i := range fill {
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fill[i] = 0
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}
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}
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return 3 * n, nil
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}
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func (e *encoder) colorTablesMatch(localLen, transparentIndex int) bool {
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localSize := 3 * localLen
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if transparentIndex >= 0 {
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trOff := 3 * transparentIndex
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return bytes.Equal(e.globalColorTable[:trOff], e.localColorTable[:trOff]) &&
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bytes.Equal(e.globalColorTable[trOff+3:localSize], e.localColorTable[trOff+3:localSize])
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}
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return bytes.Equal(e.globalColorTable[:localSize], e.localColorTable[:localSize])
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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 c == nil {
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e.err = errors.New("gif: cannot encode color table with nil entries")
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return
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}
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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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// To determine whether or not this frame's palette is the same as the
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// global palette, we can check a couple things. First, do they actually
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// point to the same []color.Color? If so, they are equal so long as the
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// frame's palette is not longer than the global palette...
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paddedSize := log2(len(pm.Palette)) // Size of Local Color Table: 2^(1+n).
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if gp, ok := e.g.Config.ColorModel.(color.Palette); ok && len(pm.Palette) <= len(gp) && &gp[0] == &pm.Palette[0] {
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e.writeByte(0) // Use the global color table.
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} else {
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ct, err := encodeColorTable(e.localColorTable[:], pm.Palette, paddedSize)
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if err != nil {
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if e.err == nil {
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e.err = err
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}
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return
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}
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// This frame's palette is not the very same slice as the global
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// palette, but it might be a copy, possibly with one value turned into
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// transparency by DecodeAll.
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if ct <= e.globalCT && e.colorTablesMatch(len(pm.Palette), transparentIndex) {
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e.writeByte(0) // Use the global color table.
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} else {
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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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}
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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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bw := blockWriter{e: e}
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bw.setup()
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lzww := lzw.NewWriter(bw, lzw.LSB, litWidth)
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if dx := b.Dx(); dx == pm.Stride {
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_, e.err = lzww.Write(pm.Pix[:dx*b.Dy()])
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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() // flush to bw
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bw.close() // flush to e.w
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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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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")
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}
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opts := Options{}
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if o != nil {
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opts = *o
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}
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if opts.NumColors < 1 || 256 < opts.NumColors {
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opts.NumColors = 256
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}
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if opts.Drawer == nil {
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opts.Drawer = draw.FloydSteinberg
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}
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pm, _ := m.(*image.Paletted)
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if pm == nil {
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if cp, ok := m.ColorModel().(color.Palette); ok {
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pm = image.NewPaletted(b, cp)
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for y := b.Min.Y; y < b.Max.Y; y++ {
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for x := b.Min.X; x < b.Max.X; x++ {
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pm.Set(x, y, cp.Convert(m.At(x, y)))
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}
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}
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}
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}
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if pm == nil || len(pm.Palette) > opts.NumColors {
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// Set pm to be a palettedized copy of m, including its bounds, which
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// might not start at (0, 0).
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//
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// TODO: Pick a better sub-sample of the Plan 9 palette.
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pm = image.NewPaletted(b, palette.Plan9[:opts.NumColors])
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if opts.Quantizer != nil {
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pm.Palette = opts.Quantizer.Quantize(make(color.Palette, 0, opts.NumColors), m)
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}
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opts.Drawer.Draw(pm, b, m, b.Min)
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}
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// When calling Encode instead of EncodeAll, the single-frame image is
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// translated such that its top-left corner is (0, 0), so that the single
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// frame completely fills the overall GIF's bounds.
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if pm.Rect.Min != (image.Point{}) {
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dup := *pm
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dup.Rect = dup.Rect.Sub(dup.Rect.Min)
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pm = &dup
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}
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return EncodeAll(w, &GIF{
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Image: []*image.Paletted{pm},
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Delay: []int{0},
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Config: image.Config{
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ColorModel: pm.Palette,
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Width: b.Dx(),
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Height: b.Dy(),
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},
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})
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}
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